Dear MorphMet group,
I have two questions related to RRPP analyses. While my request to join the *geomorph* Google group is being processed, I thought I’d post here in *MorphMet* in the meantime to ask for some guidance. Question 1: Comparing shapes between two groups in a nested design My dataset consists of shape measurements from two temperature regimes, each with 4 replicate populations (replica IDs). The design is therefore: *temperature_regime / replica_id* To test for shape differences between temperature regimes while accounting for variation among replicates, I used the following model: fit_nested <- lm.rrpp(shape_data ~ temperature / replica, data = gdf, type = "II", iter = 999) predict(fit = fit_nested, newdata = environment_replica_info) summary(fit_nested, PC = TRUE) However, the results show that the effect of temperature (R² ≈ 3.5%) is smaller than that of replica (R² ≈ 4.05%), and both are significant. I’m wondering if my nesting specification is correct. Also, the predicted shapes from predict() appear quite noisy. For comparison, I tried a simpler model: fit_env_only <- lm.rrpp(shape_data ~ temperature, data = gdf, type = "II", iter = 999) predict(fit_env_only, newdata = environment_info) summary(fit_env_only, PC = TRUE) With only two temperature levels, PC1 explains 100% of the variation, which makes me think that this analysis is not appropriate for just 2 levels. Question 2: Comparing allometric slopes between groups To test for differences in allometric slopes between temperature regimes, I used: fit_nested_allometry <- lm.rrpp(shape_data ~ temperature*size, data = gdf, type = "II", iter = 999) anova(fit_nested_allometry) I interpret this as testing whether the slopes differ between temperatures. To extract the actual slopes per each group, I’ve been splitting the data by temperature and running separate regressions within each treatment. Similarly, when I removed the allometric effects, I did this within each treatment. Lastly, I always corrected for allometry in symmetrical shape object for this analysis. If I wanted to remove allometry in the fa.component, what would be the best way to approach this? Thank you very much for your help, Daniel -- You received this message because you are subscribed to the Google Groups "Morphmet" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/morphmet2/60564fbe-46f9-48d2-9983-f60abf432f62n%40googlegroups.com.
