One set of grandparents were Okay when I was a child. The other grandmother had minus zero interest in any of her eleven grandchildren. My sister and I were forced to visit her once a month, but she saw the other nine maybe once in fifteen years. She died in 1975, and all I remember about her is that she made me a necklace made from aluminum soda pop flip tops one Christmas and was the rudest and nastiest person I had ever met. The set of grandparents turned out to be totally insane and dysfunctional. Never in a million years would they care what happened to me.
This study is very flawed. Grandparents in the U.S. were never involved in the lives of their grandchildren.