Hello, I have a repeated measures ecological data set for which I need to examine individual species-habitat responses based on site type. There are three site groupings (i.e., recent, old and control) and each site group has five sample sites (i.e., site 1-5, 6-10, and 11-15). The data were collected at the same sites over two years (i.e.,2012 and 2013), twice per year (i.e., spring and summer). In total I have four species that I need to analyze for the spring and summer data separately. The dataset also includes 5 habitat variables collected for each site (i.e., ba, std, dwd cht, and snd). I've been instructed to used stepwise regression to complete the analysis for the spring and summer data separately. I ran a t-test and noticed there are significant year effects in the species data (i.e., spring 2012 vs 2013, and summer 2012 vs. 2013). My question is, how do I perform a stepwise regression on the grouped spring 2012/2013 data taking into consideration year effects? Thank you for your assistance - Mark
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