Multivariate ANOVA (MANOVA) extends the capabilities of analysis of variance (ANOVA) by assessing multiple dependent variables simultaneously. ANOVA statistically tests the differences between three or more group means. For example, if you have three different teaching methods and you want to evaluate the average scores for these groups, you can use ANOVA. However, ANOVA does have a drawback. It can assess only one dependent variable at a time. This limitation can be an enormous problem in certain circumstances because it can prevent you from detecting effects that actually exist.

MANOVA provides a solution for some studies. This statistical procedure tests multiple dependent variables at the same time. By doing so, MANOVA can offer several advantages over ANOVA.

In this post, I explain how MANOVA works, its benefits compared to ANOVA, and when to use it. I’ll also work through a MANOVA example to show you how to analyze the data and interpret the results.

## ANOVA Restrictions

Regular ANOVA tests can assess only one dependent variable at a time in your model. Even when you fit a general linear model with multiple independent variables, the model only considers one dependent variable. The problem is that these models can’t identify patterns in multiple dependent variables.

This restriction can be very problematic in certain cases where a typical ANOVA won’t be able to produce statistically significant results. Let’s compare ANOVA to MANOVA.

## Comparison of MANOVA to ANOVA Using an Example

MANOVA can detect patterns between multiple dependent variables. But, what does that mean exactly? It sounds complex, but graphs make it easy to understand. Let’s work through an example that compares ANOVA to MANOVA.

Suppose we are studying three different teaching methods for a course. This variable is our independent variable. We also have student satisfaction scores and test scores. These variables are our dependent variables. We want to determine whether the mean scores for satisfaction and tests differ between the three teaching methods. Here is the CSV file for the MANOVA_example.

The graphs below display the scores by teaching method. One chart shows the test scores and the other shows the satisfaction scores. These plots represent how one-way ANOVA tests the data—one dependent variable at a time.

Both of these graphs appear to show that there is no association between teaching method and either test scores or satisfaction scores. The groups seem to be approximately equal. Consequently, it’s no surprise that the one-way ANOVA P-values for both test and satisfaction scores are insignificant (0.923 and 0.254).

Case closed! The teaching method isn’t related to either satisfaction or test scores. Hold on. There’s more to this story!

## How MANOVA Assesses the Data

Let’s see what patterns we can find between the dependent variables and how they are related to teaching method. I’ll graph the test and satisfaction scores on the scatterplot and use teaching method as the grouping variable. This multivariate approach represents how MANOVA tests the data. These are the same data, but sometimes how you look at them makes all the difference.

The graph displays a positive correlation between Test scores and Satisfaction. As student satisfaction increases, test scores tend to increase as well. Moreover, for any given satisfaction score, teaching method 3 tends to have higher test scores than methods 1 and 2. In other words, students who are equally satisfied with the course tend to have higher scores with method 3. MANOVA can test this pattern statistically to help ensure that it’s not present by chance.

In your preferred statistical software, fit the MANOVA model so that Method is the independent variable and Satisfaction and Test are the dependent variables.

The MANOVA results are below.

Even though the one-way ANOVA results and graphs seem to indicate that there is nothing of interest, MANOVA produces statistically significant results—as signified by the minuscule P-values. We can conclude that there is an association between teaching method and the relationship between the dependent variables.

## When MANOVA Provides Benefits

Use multivariate ANOVA when your dependent variables are correlated. The correlation structure between the dependent variables provides additional information to the model which gives MANOVA the following enhanced capabilities:

**Greater statistical power**: When the dependent variables are correlated, MANOVA can identify effects that are smaller than those that regular ANOVA can find.**Assess patterns between multiple dependent variables**: The factors in the model can affect the relationship between dependent variables instead of influencing a single dependent variable. As the example in this post shows, ANOVA tests with a single dependent variable can fail completely to detect these patterns.**Limits the joint error rate**: When you perform a series of ANOVA tests because you have multiple dependent variables, the joint probability of rejecting a true null hypothesis increases with each additional test. Instead, if you perform one MANOVA test, the error rate equals the significance level.

Bailey W says

Hi Jim,

This post has been extremely helpful in understanding what data analysis i need for my thesis, however, can you help clarify if im on the right track for using MANOVA. I have three IV’s (persisters, remitters, and controls) and three DV’s (Tests – Flanker, Stroop, Parent Report) with data being assessed at 8 years old and then 18 years old, would MANOVA suit this sort of analysis?

Regards,

Bailey

Jim Frost says

Hi Bailey,

Yes, if the DVs are correlated, then MANOVA is a good choice. If they’re not correlated, just use regular ANOVA.

Jay says

Hi Jim,

I’m experiencing a similar quandary, however, my IV is continuous (Autism quotient score). I’m assuming from your response that it does not matter that there is only one IV. And MANOVA is a perfectly acceptable tool in these scenarios.

Thanks for your continued assistance.

Best,

Jay

Vree says

Hi Jim , I have a question.

I am currently conducting a final year thesis study with 1 independent variable (Gender) and 3 dependent variables (Perceived stress, anxiety and loneliness), titled Gender differences in Perceived stress, anxiety and Loneliness among International Undergraduates during the Covid-19 pandemic. I am trying to find if there are gender differences on the 3 variables. Can I run a one way independent anova 3 times for this study or a Manova?

I am genuinely confused as what to run because I only want to see the differences of gender.

Thank you in advance!

Vree

Jim Frost says

Hi Vree,

The answer is you can do it either way. Often times it’s just simpler to understand regular ANOVA results. You can try one-way ANOVA first with three separate models to see what results you get. However, if that doesn’t work *and* those three DVs are correlated, you can try using MANOVA. MANOVA does have some benefits as I point out in this article but it can be harder to interpret. So, if your ANOVA results for separate models seem to miss something you expect to be there, try MANOVA.

I hope that helps!

Alice says

Yes, I read your article about two-way ANOVA just now and it definitely cleared my confusion. Thank you so much for all your help. I really appreciate it.

Jim Frost says

You’re very welcome, Alice!

Alice says

Thank you so much for your help. Just one more question again. I came across a lot of Youtube tutorials employing Univariate analysis in SPSS to see the interaction effect of the IV’s on the DV when they have two IVs and one DV, like in my case. Will it be correct if I do the same?

Jim Frost says

Hi Alice,

If you’re performing ANOVA you’re not performing univariate analysis. Univariate analysis is the simplest type of analyses because you have just one variable. The simplest form of ANOVA requires TWO variables. One-way ANOVA requires one IV and one DV.

Additionally, if you’re talking about interaction effects, you’ll need a minimum of three variables. 1 DV and 2 IVs. An interaction involves at least two IVs. So, if you’re performing univariate analysis or one-way ANOVA, you cannot consider interaction effects. Typically, you’d be using at least two-way ANOVA or multiple regression.

I believe you’re talking about ANOVA because you’re posting in the comment section of an ANOVA post. So, I’ll refer you to my article about two-way ANOVA. In it, I talk about interaction effects amongst other topics. I also have an additional article about interaction effects you might want to read. However, read the two-way ANOVA post first because it covers the number and types of variables you need.

Wagner Fontes says

Hi Jim,

Thank you for this post. You did a great job in explaining the concepts.

If I may ask, I have one question:

If I had a thousand of dependent variables, How could I be able to interpret and draw groups of correlation among them using MANOVA?

A real-world example for that would be the quantification of a thousand proteins from cells in three different conditions (control, treatment 1, treatment 2). Currently I’m using ANOVA to analyze each one, but I’m pretty sure many of them are correlated, involved in connected cell-signaling pathways.

Thank you for your time!

Jim Frost says

Hi Wagner,

Wow, so a thousand dependent variables. That would be quite the knot to untangle! The same principles would apply but the results would be vastly more complex because you’re talking about multivariate relationships between a thousand DVs plus whatever IVs you have. I think it would require a custom solution to be honest that incorporates subject-area knowledge.

Radhika says

Hi,

Thank you for the informative and easily understandable post.

Can you please suggest a statistical measure for my data; I have three independent variable and eight dependent variables. The DVs are not correlated, for ex. DV1 mean 1.5 and DV5 mean 350.

Thank you very much

Alice Kenye says

Hi Jim,

Firstly, thank you so much for this useful blog. You are a blessing to many of us who are struggling with statistics.

Please give me some advice on the following question.

I have two independent variables and one dependent variable and I also want to see whether there is an interaction effect of those two IVs on the DV. Would it be better to employ MANOVA instead of using ANOVA?

Jim Frost says

Hi Alice,

You should use ANOVA because you have only one dependent variable. Because you have two IVs (presumably categorical), you should use two-way ANOVA. Click the link to see where I show examples of two-way ANOVA.

LadyMae says

Wow! Thank you so much for this, Jim. I’m currently working on my final year thesis and I’ve been confused as to whether to use ANOVA or MANOVA. It’s a lot clearer now. Thanks again!

Kehinde Ogunbiyi says

Hi, I am currently conducting a study on the effects of student type (domestic or international) on levels of trait emotional intelligence, mindfulness, emotional distress and perceived stress. I used a MANOVA analysis which found non-significant differences in three of the variables but not one. I would like to analyse the variable with the difference, Would I need to run a post-hoc (which apparently isn’t possible because there are less than three categories) or can I simply say the mean differences as it appears in the estimated marginal means?

Oksana says

Thank you very much!) This information helps a lot!

Oksana says

Dear Jim,

First of all, I hope you are safe in these worrying times of disease.

I want to thank you for your wonderful posts on statistics. They make things much clearer!

And if I may I also wanted to ask a question: you say that to apply MANOVA, dependent variables should be correlated, but I wonder if the sign of correlation matters? I mean should all the DVs be positively correlated, or they could be both positively and negatively correlated? For example, I have 5 DVs, and there are both positive and negative correlations between them, is it still possible to apply MANOVA in this case?

Thank you very much.

Kind regards,

Oksana

Jim Frost says

Hi Oksana,

No, the correlation sign doesn’t matter. All that matters is that the correlations among the DVs exists because it provides more information for the model to assess. It’s ok, and even good, to use MANOVA in the situation you describe with a mix of positive and negative correlations.

Ajab tareen says

Thanks Jim for your to the point reply, sure my dependent variable are correlated so i used MANOVA, Now i have both significant as well as non-significant result for DV, but stuck how to identify which one is significant among the five cultivars for a particular dependent variable.

Ajab tareen says

Hello Jim, Feeling pretty good to see your posts regarding statistics. I am going to analyze my research data. I had taken 5 different apple cultivars and determined TPC, TFC, mineral contents etc. Now which type anova would be good to analyze the data.

Jim Frost says

Hi Ajab,

I’m glad you like my posts!

It sounds like you can either use one-way ANOVA or MANOVA. It appears that you have one factor: apple cultivar. This factor forms the five groups. If your dependent/response variables are correlated, then I’d consider using MANOVA for the reasons I mention in this post. If they’re not correlated, consider performing one-way ANOVA multiple times for each of the DVs. While performing multiple tests can increase the family-wise error rate, it’ll be easier to interpret.

Sumit Mishra says

Can we use individual ANOVA rather than MANOVA since MANOVA is a considerably more complex design than ANOVA and therefore there can be some ambiguity about which independent variable affects which dependent variable. The dependent variables should be largely uncorrelated for MANOVA. If the dependent variables are highly correlated, there is little advantage in including more than one in the test given the resultant loss in degrees of freedom. Under these circumstances, use of a single ANOVA test would be preferable (French et al., 2008)

http://online.sfsu.edu/efc/classes/biol710/manova/MANOVAnewest.pdf

Do you agree?

Jim Frost says

Hi Sumit,

I agree that MANOVA models are more complex and interpreting the results can be more difficult. However, some cases really require it. I show one such case in this blog post where if you don’t use MANOVA, you completely miss the findings! I’d say try using ANOVA and see what you get. However, if you have multiple correlated DVs, there are some occasions where you might really need to use it. And, I disagree with what you right about using MANOVA for uncorrelated DVs. If your DVs are uncorrelated, you have less reason to use MANOVA. If they are correlated, you have more reason. Again, this post indicates one such scenario!

David Sanderson says

Jim,

I have a question on how far can we expand the independent and defendant amount. In my case I have 5 different offices types (independent variables) and a scores for 32 different categories (dependent variables). Can a MANOVA test distinguish if there is any significant differences between the office types and how would the data be interpreted?

Thanks David

Danielle says

Hi Jim,

I’m in the toxicology field and my project involves assessing the effects of 5 different compounds, with various concentrations of each, in wild type and mutant animals. I think in this case I would have 3 independent variables, right? Compound, concentration and animal strain. However, if I’m making all these comparisons, I’m losing power. So what I don’t understand is why a result would be statistically significant in a scenario were I would have, for example, only one compound, one concentration and one strain, but if I have multiple of each, this same result wouldn’t be statistically significant? Hopefully I made myself clear! Thank you for your website, you make statistics much more fun!!

100womenloudoncounty says

Hi Jim,

My study includes one independent variable with 3 levels (participation in one of 3 networks) and 3 dependent variables which are likely to be correlated (teacher expectations, teacher self-efficacy, and teacher collective efficacy). I want to determine which networks result in higher scores of these factors. I am having trouble wording my questions though and thinking about what information the MANOVA will tell me. I originally worded it as.. Is there a relationship between network membership and scores of teacher expectations, self-efficacy, and collective efficacy? But, to me this implies more of a correlation, which is not possible because it is not two pieces of ordinal data. Should I word it as differences instead? And is it possible for example that more than one network will show a statistically significant relationship to a DV or multiple DVs? Should I have a research question which addresses the possible correlation of my DVs?

I don’t know if that makes any sense. I know what I’m trying to investigate, but I’m not sure how to word the questions and I also wonder how specific I should make my hypotheses. For example, I suspect one network will be statistically higher in teacher expectations and possibly collective efficacy. But, I also see the potential for another one to be statistically higher in collective efficacy in regard to another.

Is it possible to stick with the relationship question and then have a hypothesis that predicts a relationship between more than one IV and the same DV?

Desiree Tse says

Hi Jim,

Thanks for the informative post. I am wondering if only Roy’s largest root is significant out of the 4 MANOVA tests, would you still take the result as significant?

And how to interpret a quadratic interaction between my within and between subject variables?

I am testing my participants’ memory on emotional faces, which have been categorized into negative, neutral and positive faces for data analysis. They are also the within subject DVs, while I got 2 clinical populations and 3 treatment conditions as my between subject variables.

If MANOVA doesn’t work, what other tests would you recommend? I am interested in the interaction between the between subject variables.

Thanks,

Desiree

Michaela says

Hi Jim,

thank you for an informative post! I am currently designing a grant proposal and have always struggled with stats so I was wondering if you could please help me out. I want to be looking at the differences of autistic and neurotypical adults’ performance on reading facial and body language expressions – there will therefore be two populations (autistics vs. non-autistic) and 3 conditions (one where only faces are shown (2 types of emotions will be displayed)), one where only bodies are shown (again, 2 types of emotions will be displayed), one where faces and bodies are both shown (either displaying congruent or incongruent emotions)). All participants will be completing all the conditions.

Previous papers that have looked into this used repeated measures ANOVA, however what I want to do is have all participants complete a couple additional questionnaires that will be looking into a condition that is often associated with autism (alexithymia) – it is therefore very possible that my populations will look something like neurotypical adults with low score for alexithymia, neurotypical adults with high score for alexithymia vs. autistic patients with low score for alexithymia, and autistic patients with high score for alexithymia. The presumption is that autistic patients with high score for alexithymia will perform worst, while neurotypical adults with low alexithymia score will perform best.

The aim of the project is to determine to what extend do autism and alexithymia contribute to the impairment of expression recognition (individually and combined) – is it still okay to use ANOVA or would MANOVA be better? Or am I meant to be running a regression analysis? Any post-hoc tests that should be considered?

Thank you very much for your help!

Best,

Michelle.

Laura says

Dear Jim, thank you very much, your reply was very helpful!

I have now performed the MANOVA analyses and have found that one of my group variables, variable A, (described in my first post) best discriminates between brain measures (the outcome measures), and would like to follow up on this with a post-hoc test. Variable A consists of group 1, 2, 3 and 4 and I would now like to know if one of these groups is driving this effect. Could you please tell me if this is possible to test and what would be the best way to do this? I have read online that ANOVA is sometimes used to follow up, but I am not very interested to see which groups are associated with brain measures, I just want to know which groups differ across all brain measures.

Thank you so much in advance!

Best,

Laura

Jim Frost says

Hi Laura,

It sounds like you need to perform a post-hoc test to determine which groups are significantly different from the others for variable A. Post hoc tests a common follow up for both MANOVA and ANOVA. MANOVA and ANOVA tell you that there is a significant effect while the post hoc tests help you map out the nature of those effects–which groups are significantly different from the others.

I hope this helps!

Jessica says

Hi Jim,

Thank you for a useful and informative post.

I was wondering if you could help me with a question.

I am conducting a study looking into the effectiveness of a post-therapy relapse-prevention intervention in maintaining treatment grains after therapy. Questionnaires measuring treatment gains quantitatively (e.g. mood) are taken at three time points: pre-therapy (T1), on completion of the therapy (T2) and 2 months after the therapy (T3).

I am comparing a control group completing therapy but without relapse-intervention with a group who receive the relapse-prevention intervention between T2 and T3. In order to test the effectiveness of the intervention, I want to see if the IV (intervention group or control group) predicts the DV (change in outcomes between T2 and T3).However, the DVs are correlated AND I will need to account for the change in outcomes from T1 to T2 (a covariate) and so I thought an MANCOVA would be appropriate.

So I have 2 IVs and 4 DVs.

However I have a much smaller sample size that I had first intended (n=15 per group – total n=30). so my question is is this too small a sample size to conduct a MANCOVA with? If so, what would be a better option?

I hope this makes sense.

Many thanks in advance!

Jessica

Jae says

Hi Jim,

I’m doing a study with 1 IV and 3 DVs. In theory, my 3 DVs should be at least weakly correlated, although my results do not show this. 2 of them are very strongly correlated (r is very close to +1), while the third is not correlated at all with either of them. Can I still use a MANOVA? or should I do 3 separate ANOVAs instead? If I were to do the ANOVAs separately, is there a way in which I reduce the Type I error?

Thank you in advance.

Jim Frost says

Hi Jae,

It still sounds like MANOVA would be helpful given the correlations. Although, you probably should investigate why the correlations are so high between a pair and non-existent with the third variable when that doesn’t match your theory. It almost sounds like two variables practically measure the same thing and third isn’t related at all. It’s not necessarily wrong, but worth investigating because they don’t match your expectations. You should check to be sure that you’re measuring what you think you’re measuring, and that there were no measurement/data entry errors.

Best of luck with your analysis!

steph says

HI, thanks for your kindly help. I have a doubt.

I have a IV with 2 groups (control/experimental), and one DV (sensory processing). However, the DV has 4 main scales. The way in which I measured was through a questionnaire that doesn’t have a single scores, but 4 scores per each scale. So, is it appropriate using a MANOVA with my DV plus 4 IV??

Jim Frost says

Hi Steph,

If those four scales are correlated to some extent, then it sounds like you’d get some real benefits out of MANOVA. If they’re not correlated, you can just run separate ANOVA analyses for each scale. Actually, because there are just two groups, you can use t-tests if they’re not correlated. But, yes, if the four scales are correlated, definitely consider MANOVA! MANOVA provides benefits when the DVs are correlated.

Litsa says

Hi Jim,

Thanks so much for the post! I have a question. Can we use MANOVA when we have more than one independent variables? I have a design in which I am testing 4 dependent variables and I have 4 independent variables also. I have used lmer in R so far for each of the 4 dependent variables looking at the influence of the independent variables. Do you think I should use MANOVA? My dependent variables are correlated.

Jim Frost says

Hi Litsa,

Yes, it sounds like MANOVA is a good possible analysis to try with your dataset. You can use more than one independent variable. And, it provides the most benefits when the dependent variables are correlated.

Best of luck with your analysis!

Sylvia says

Hi Jim – your blog post and the follow-up questions and your replies are very helpful and much appreciated. Would you please advise on the following questions – is MANOVA most appropriate here and what should the sample size be per group? We have 3 groups who will be measured once pre-operatively and 4 times post-operatively. There are 13 measurements, which can be grouped as patient-reported outcomes (5 measures; means) and clinical outcomes (8 measures, means). We want to compare pre- and post-op differences by group and also compare post-operative measures between groups. We expect there to be some correlations among the measures in both the patient-reported outcomes and the clinical outcomes. We also have 10 measures of patient characteristics (e.g., age, gender, BMI, etc.; 4 means, 6 categorical) that we want to compare by group. I hope I’ve provided enough information for you to advise on this. Thanks!

Ifedayo Adu says

Hello Jim,

Good day Jim. I find your articles on statistics quite interesting. However, I need you to help me with a statistical issue. Please may I know why a researcher would decide not to introduce a moderating variable in a model. Thanks for your anticipated assistance.

From,

Adu Emmanuel.

Jim Frost says

Hi Adu,

Moderation effects are included in models as interaction effects. Read my post about interaction effects for more information.

The only legitimate reasons that I can think of for why analysts would not include an interaction effect in the model are either because the effect is not statistically significant or because theory very strongly suggests that the interaction effect is not appropriate for the model.

If interaction effects are significant and appropriate for the subject area, you risk extreme interpretation problems by not including them in the analysis. You can read about that in the post I link to!

Meysam says

Hi Jim,

Thank you for this helpful information about MANOVA,

I have a question, In one of the study I have done for my PhD, I have two independent variables, each categorical with two levels, and I measured 3 dependent variables which are correlated. I also have a covariate.

Q1: First of all the data significantly violated the assumption of homogeneity of covariance (p<.00000), considering this can I use the Mancova test (my sample size in each of four groups is about 95, in total 380)?

Q2: When I do a separate ANCOVAs on each dependent variable I have significant result for both IVs, however, when I use MANCOVA the effect of one of my IV becomes non-significant, which test should I report in my thesis?

Thank you

Minie Bulay says

hello Jim, I find your blog very useful especially for those struggling in this realm of statistics, like me. I just want to ask, the way of framing questions in MANOVA, like when my IVs are Sex and Study Habits, and the DVs are the Learning gains, GPA and NAT scores? how will I state if MANOVA applies for this?

Jim Frost says

Hi Minie,

If your DVs are correlated, then MANOVA becomes a more powerful analysis because it can use the correlation between the DVs to increase the statistical power. It can also detect multivariate effects that ANOVA can’t, which I demonstrate in the blog post. If your DVs are not correlated, then MANOVA doesn’t really provide additional benefits compared to ANOVA.

I hope this helps!

laura says

Hi Jim,

Thank you for this very informative post! I hope you could give me some advice regarding the following issue:

I am trying to examine which of two group variables best map to underlying brain measures. I have two independent (group) variables (say A and B) and around 30 dependent variables. I would like to examine whether group variable A (group 1,2 or 3) or B (group i,ii,iii) best discriminate groups based on these brain measures. I was thinking of running MANOVA twice, once with variable A and once with variable B, but is there a way to test whether these results are signficantly different so we can conclude for instance that group variable A best maps to underlying brain measures?

Thanks very much in advance!

Best,

Laura

Jim Frost says

Hi Laura,

It makes me happy to hear that you found the post to be helpful!

MANOVA will help you out if those 30 dependent variables are correlated amongst themselves. With so many dependent variables, you will have to be aware of sample size concerns. I’ve written about how to ensure that your linear model has a sufficiently large sample size based on the independent variables and other terms in the model. I don’t know how the number of dependent variables factors in, but it’s something to keep in mind.

As for determining which categorical variable is better, you can try including both in the model at the same time. This approach can give you some valuable head-to-head comparison information. You might also want to read my post about identifying the best independent variable. I write about this in the context of regression models, but it’ll give you some good ideas to consider and other things that you should disregard.

I hope this helps!

Pamela Marcum says

Wow, thanks Jim for taking the time to write such a wonderfully detailed and helpful reply, and for providing links to your other posts for much-needed background reading. Can’t express enough how appreciative I am of your willingness to share such hard-earned knowledge with others!

Sarah says

Hi Jim, Thank you for this blog. Do you by chance have a reference for you last section “When MANOVA Provides Benefits”?

Jim Frost says

Hi Sarah, I don’t have a specific reference but these are commonly understood benefits of MANOVA. I’d imagine that any textbook that covers this analysis will confirm them.

Pamela Marcum says

Hi Jim,

First of all, thanks so much for this extremely informative and comprehensive blog. I’m thinking that MANOVA might be exactly the tool that I need for a problem that I am currently grappling with, but an additional “twist” in my data might actually invalidate the use of MANOVA. So here goes (I am an astronomer): I have a plot of gas mass normalized by luminosity (y axis) versus luminosity (x axis) for a large control sample of galaxies. This plot is a nonlinear relation in which dimmer galaxies generally have higher normalized gas masses. Overlayed on this plot is a (smaller) sample of galaxies that is the focus of my research. If I squint and look sideways at the plot, I think that my sample trends towards having somewhat larger normalized gas mass as compared to the control objects with similar luminosity.

I’d like quantify the statistical significance of any gas mass enhancement in the small/study sample. Here’s the problem: the smaller set of data mostly bunches up at the low-luminosity end and as a result does not cover the full range of X values (luminosity) represented by the control sample and therefore does a poor job of sampling that relationship. Because the smaller set of data are at the low-luminosity end, they are expected to have higher normalized gas mass (that’s what the relationship defined by the control sample shows), so the fact that the study sample objects are generally gas-rich is not what is surprising. What WOULD be interesting is if those galaxies have MORE gas mass than what would be predicted by the relationship for their given luminosity.

My concern is that the smaller sample being so heavily skewed towards one end of the X-axis and not “adequately” sampling along the same range of X values as the control sample will invalidate any MANOVA application (?) On the other hand, there is nothing about the example you provide above that would have excluded the possibility that “satisfaction” would have been skewed to one of the extremes for one of the exam methods. In that example, however, the sample sizes being compared are equal (or nearly so), unlike my situation.

If MANOVA is definitely not the tool for my situation, would a better approach be to just truncate the control set so that the same x values are covered between both samples, and then apply a 1-dimensional test to the Y-axis parameter ? (A steeply-rising “knee” in the gas mass to luminosity relationship in the mid-range of the x-axis would be mostly clipped out if a truncation to the control sample was performed. Losing the information of this underlying relationship in any statistical comparisons between these 2 data sets could be an undesirable consequence?). Thanks for any advice you might have, particularly with regards to the robustness of the MANOVA test to such a situation in which one sample is seriously skewed towards one end of the x-axis relative to the other, and has significantly fewer data points than the other.

Jim Frost says

Hi Pamela,

First, I just want to let you know that I LOVE astronomy. I totally don’t have any official education in it but I love to absorb as much of it as possible! In a parallel universe I’m an astronomer or maybe a physicist!

I think what you need to do is actually fit a regression model and include an sample indicator variable and an interaction term. The gas mass normalized by luminosity would be your dependent variable and luminosity would be an independent variable. You’d also need to include an indicator variable that identifies whether the data are from the control sample or your sample (you’d need to put all the data in one data sheet). Then include a two-way interaction term (luminosity*sample indicator). You should also include the indicator variable as a main effect/independent variable. Collectively the indicator variable and interaction term will tell you whether the relationship between the independent and dependent variable is different between your sample and the control sample. The main effect for the indicator variable will tell you if the relationship is shifted up or down on the X-Y scatterplot. The interaction effect tells you whether the slope is different. Use the p-values for these terms to determine whether each one is statistically significant.

I *think* that is what you need to do based on your description. I’ve written a couple of posts that describe this process that you should read:

Comparing Regression Lines

Understanding Interaction Effects

There is one possible complication that I can see with your scenario. You mentioned that it is a nonlinear relationship. The way forward depends on whether that is nonlinear in the common meaning of the word (i.e., the line isn’t straight) or in the exact statistical sense. The process I describe above works for linear models. But linear models can fit curves using a variety of methods. However, if it’s truly nonlinear in the statistical sense of the word, you’ll need to use an entirely different and unfortunately much more complex methodology. I’ve written two posts that should help you answer that question. The first defines the differences between linear and nonlinear in the world of statistics. The second walks you through the different ways of fitting curves using an example dataset.

The Difference Between Linear and Nonlinear Regression

Curve Fitting Using Linear and Nonlinear Regression

Hopefully a linear model will fit because that’s a lot more straightforward to work with! Oh, and about your sample being skewed towards one end of the range, I don’t think that’s a problem. You should be able to determine whether the same relationship applies to both samples or not. One issue I see is if the two samples don’t overlap. In that case, if the relationship is different, it might be hard to determine whether the difference is due to whatever the defining characteristic of your sample is or just because you’re in a different range of the data. Sometimes the relationship can change for the same type of data as you move along the range of data.

At any rate, I hope this helps!

Jim Frost says

Hi again, one more thought in addition to my previous reply. Given that there is curvature in your data, it probably is a problem that your data just covers a portion of the range. You won’t be able to use the same model because if it’s just a portion it won’t have the same curvature most likely. You might need to truncate the control sample data to fit the same range of data that your sample covers. I’m not sure how many data points the sample data has in that range or if there might be other subject related concerns for that approach. But, it would let you compare the models for the same range of data and if the curvature was different within that range, it would be meaningful. Whereas if you compared your range to the full range, the difference wouldn’t be meaningful.

Omotayo says

Thanks for your kind response.

Omotayo says

Hi Jim, I need more clarifications, your comment on this subject seems to be tending towards my needs. However, my question is, between ANOVA and Manova, which of them is suitable for an hypothesis stating that, there is no deference between male and female in terms of impact of Staff development policies, practices on job performance. Thanks for your response in anticipation.

Jim Frost says

Hi Omotayo,

If gender is your independent variable and staff development policies and practices on job performance are your dependent variables, and those two DVs are continuous variables that are correlated, I’d recommend MANOVA.

Jim

Esther says

Hi Jim! Thank you for your informative article, the concepts are so much clearer to me now.

However, I have a question.What if I have 4 independent variable but only 1 dependent variable? Would ANOVA be able to process that? Or should I employ MANOVA?

Jim Frost says

Hi Esther, It makes me happy to hear that my blogs have helped clarify things for you!

MANOVA requires multiple dependent variables. It is particularly useful when those dependent variables are correlated.

When you have only one dependent variable, you have to use an ANOVA procedure. With some ANOVA procedures, such as General Linear Model, you can have multiple independent variables.

I hope this helps!

Gemma says

Hi there,

So what would be the difference between a 2-way ANOVA and a MANOVA? When would you use them and why? Is one more powerful?

Thanks so much!

Jim Frost says

Hi Gemma,

There are several differences. For one thing, 2-way ANOVA can handle two independent variables (IV) and only one dependent variable (DV). MANOVA can handle 1 or more IVs and 1 or more DVs. The real key advantage of MANOVA is how it handles multiple DVs at the same time. This provides MANOVA with more power when those DVs are correlated.

Use MANOVA when you have multiple DVs that are correlated. As this post shows, it can detect multivariate patterns in the DVs that ANOVA is simply unable to detect at all. Plus, it is more powerful when those DVs are correlated.

When you have only one DV, use some form of regular ANOVA, which includes 2-way ANOVA.

I hope this helps!

Tan says

Hi Jim,

I have a few questions:

IV = independent variable

DV = dependent variable

1. Suppose I conducted 2 x 2 x 2 factorial design using Manova. My hypotheses cover the direct effect, two-way interaction, and three-way interaction.

I found that based on the direct effect, IV1, IV2, IV3 are significantly related to DV1 and IV1 is the most important factor. Furthermore, interaction effect of X2 and X3 also significantly related to DV1.

When writing the discussion part in paper, I provide that reasons why IV1, IV2, IV3 are significantly related to DV1, then do I need to explain IV1 is the most important factor? If not, why?

Finally, I discuss the interaction effect.

2. I understand that SPSS will run Manova and then run Anova automatically. The reason is that if the program run Anova in several times, the type I error will increase. Am I correct?

Thank you very much

Joe Smith says

Dumb question: What test or tests does one run in SPSS to find out if the dependent variables are related, to “gain the benefits of MANOVA” as you say. Thank you sir!

Joe Smith says

correlated rather

Jim Frost says

Hi Joe, of course there is no such thing as a dumb question! All you need to determine is if they are correlated. So a simple Pearson’s correlation. Or, you can even use regression analysis. Nothing fancy! As long as there is some sort of relationship between the dependent variables, MANOVA is beneficial.

Aba Merci says

Hi Jim,

Could please explain why computing a variance of several numbers is like analyzing their differences

Jim Frost says

Hi Aba,

To calculate the variance (which is the square of the standard deviation), you take the difference between each individual value and the mean, square those differences, add all of those squared differences together, and then divide by the number of observations. If you want the standard deviation, which is easier to interpret, you need to take the square root of that.

So, you’re really analyzing the differences between the individual observations and the mean. A larger variance (or standard deviation) indicates that the differences between the individual data points and the mean tends to be larger (the data points tend to fall further from the mean–they’re more dispersed). Smaller values of the variance/standard deviation indicate that the differences are smaller. The data points are clustered more tightly around the mean. That’s how differences come into play with the variance and standard deviation!

I hope this helps!

Sophia says

Hi Jim,

Thanks for writing this very informative post! I am in my final year of Applied Psychology and am currently in the process of completing my final year project. My study is investigating whether a difference exists among the eating patterns and behaviours of college students of the different years (i.e. 1st-4th year college students). My independent variable would be college year and my dependent variables are: (i) eating patterns, (ii) emotional eating and (iii) attitudes towards healthy eating. Would you recommend me to use a MANOVA in analyzing my data or would you recommend a different approach to analyses? I am confused on what approach to use!

Best,

Sophia

Jim Frost says

Hi Sophia,

If the dependent variables are correlated, then you gain benefits by using MANOVA rather than ANOVA. However, if they are not correlated, ANOVA might be just fine. I’m not an expert in that field, but it seems like your dependent variables might be correlated.

I hope this helps. Best of luck with your analysis!

feafeafeaf says

DVs aren’t supposed to be correlated

Jim Frost says

Hi, you’re thinking about

independentvariables. When independent variables are correlated it is known as multicollinearity, and it can be a problem. I’ve written a post about multicollinearity in case you are interested.Most analyses aren’t designed to handle multiple

dependentvariables. However, MANOVA is not only designed for that but there are benefits when they are correlated.