Testicular volume & scrotal circumference of twelve bulls were measured repeatedly. The bulls were divided into two categories (young versus old). We are interested in investigating the effect of age group (Independent variable) on testicular volume & scrotal circumference (dependent variables). Can someone please advise which test we should use? I think repeated measures MANOVA?
SAS performs both univariate and multivariate repeated measures analyses. It can assist you in analyzing this data on repeated measures..
The easy one is : By using the SAS PROC MIXED PROCEDURE, you will be able to model the covarinace structure for the repeated mesures factor, you have here another random factor which is "bull" and at least one fixed factor age ( young vs old) .... It seens to me the optimal way, because you may test several covarinace structures for the repeated measures factor, say for example: equal covariance a varianze; unequel variances an equel variance; autoregressive; unestructured etc.
In SAS the other way is to consider each measurement as a response variable, to consider the fixed effects and to perform a multivariate analysis with the MANOVA statement.... Several contrast are available for this purpose.
The old way was to consider equal variance and equal covariance, that is a REPEATIBILITY model, which may be not appropiated, but considering what is posted in paragraph two, it could tell you based on the sphericity test that it could be appropiated.
In summary I would suggest you the PROC MIXED procedure, is more flexible.
Best regards.
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