diff --git a/05-Reliability.Rmd b/05-Reliability.Rmd
index 70984385..7f9447f7 100644
--- a/05-Reliability.Rmd
+++ b/05-Reliability.Rmd
@@ -662,6 +662,7 @@ pio_cross_dat <- data.frame(Person, Item, Score, Occasion)
 Reliability is not one thing.\index{reliability!types of}
 There are several types of reliability.\index{reliability!types of}
 In this book, we focus on [test–retest](#testRetest-reliability), [inter-rater](#interrater-reliability), [intra-rater](#intrarater-reliability), [parallel-forms](#parallelForms-reliability), and [internal consistency](#internalConsistency-reliability) reliability.\index{reliability!types of}
+Moreover, one can estimate reliability at different levels (e.g., person-level versus group-level) [@Geldhof2014; @Hove2022].\index{reliability!types of}
 
 ### Test–Retest Reliability {#testRetest-reliability}