### Group-mean centering for multilevel models

When using multilevel models, researchers will often want to group-mean center variables to aid in interpretability. This tool, implemented in R, centers variables by group/cluster.

Commented R code available here: [Link]

Written by Doc Edge; Modified by Eric Hehman

### Sampling from data to assess when averages are stable

Across diverse areas of research, it is common to average a series of observations, and to use these averages in subsequent analyses. Research using this approach faces the challenge of knowing when these averages are stable. Meaning, to what extent do these averages change when additional observations are included? Using averages that are not stable introduces a great deal of error into any analysis. The current research develops a tool, implemented in R, to assess when averages are stable. Using a sequential sampling approach, it determines how many observations are needed before additional observations would no longer meaningfully change an average.

Commented R code and tutorial found here: [Link]

Based on working paper found here: [Link]

Written by Gabe Nespoli, Sally Xie, Eric Hehman

### Estimating ICCs in cross-classified multilevel models

Estimating ICCs can inform researchers as to what percentage of variance in their variable of interest is coming from different levels of the multilevel model. For instance, research here uses these models to estimate the percentage of variance in person perception ratings originating from between-perceiver and between-target differences.

Commented R code and tutorial found here: [Link]

Based on paper found here: [Link]

Written by Eric Hehman

### Bootstrapping confidence intervals around ICCs

Researchers may wish to compare ICCs to one another. For instance, to test whether between-target variance in appearance (i.e., target-ICC) contributes to evaluations of women more so than men. This code modifies the lmeresample() package in R (which modifies the boot() function) to bootstrap 95% confidence intervals around ICC estimates. The 95% CIs of each ICC can then be examined for overlap to determine if they are different.

Commented R code and tutorial found here: [Link]

Based on paper found here: [coming "soon"]

Written by Sally Xie