compute cooks distance with influence

pymer4/models/Lmer.py

@@ -1684,7 +1684,8 @@ def cooks_distance(
         self,
     ):
         """
-        Compute Cook's distance for a Lmer object (this is a wrapper for cooks.distance in lme4).
+        Compute Cook's distance for a Lmer object. Specifically, we use cooks.distance(influence(x) as discussed in 
+       https://github.com/lme4/lme4/issues/693
         Args:
             self (Lmer): the Lmer object for which confidence intervals should be computed
 
@@ -1708,7 +1709,7 @@ def _f(x):
          # Model cooks distances
         rstring = """
             function(model){
-            out <- cooks.distance(model)
+            out <- cooks.distance(influence(model))
             out
             }
         """