To everyone who could help me:
I'm performing a length-weight relationship in two populations of a single species of caridean shrimp (they are from two distinct seasonal periods). The pooled data was divided into males, females, non-ovigerous females and ovigerous females. I performed the equation and obtained the b slopes of every sub-sample analyzed (included the pooled data), which account for ten b slopes values in total, but now I want to compare those slopes to know if there is any difference between them (i.e. males from one season vs males from another, OR males vs females from different seasonal periods, or the same but contrasting females vs non-ovigerous or vs ovigerous females, etc.).
I read that an ANCOVA can do comparisons of this kind, to see if there is some differences regarding the effects of seasons and the sexual state (males, females, non-ovigerous and ovigerous) on the b slopes (growth type). I use SPSS (don't know how to use R by the way) and I'm having a rough time trying to determine the way in which I should put my data on the program. One of my problems is that, since I want to compare the b slopes and see if there is difference in the grow-type, and that the b slopes are the result of the relationship between the length and weight, I'm not really sure how to proceed. Should I paste all my length and weight data on the program? and then when I perform the ANCOVA, how can I relate both length and weight in the ANCOVA to let the program "know" that I want to compare the slopes?!. Because I assume it is not as simple as comparing the single b slopes values, because I only have ten of them.
Regarding the variables, I'm assuming that my dependent variable is the weight, the length is the covariate, seasonal period (dry and rainy) and sexual state are my factors (In terms of the spss).
Another issue here is that it seems that ANCOVA can not perform post-hoc test to see differences among groups, so if there is indeed differences then what should I do? an ANOVA?
I really have tried to find some guidance with similar data on the internet, but since my case is specific in the field, the examples I ran into are too general (like a statistic class) and the papers doesn't show you all the details, they just simply report the p values, tell you they used ANCOVA and that's all. I'm looking for a really walkthrough explanation of how to process my data to perform the statistics.
Thank you very much for your attention.
Best regards.
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