One strength of IJzendoorn's study is that is uses a large sample size.Results can be generalised and patterns can be found. Eliminates possible effects of anomalous results. Meta-analysis is particularly useful in this topic.
Imposed etic
One weakness of IJzendoorn's study is that constructs from one culture are wrongfully applied to another. All data was based entirely on the Strange Situation study. Applying American values to cross-cultural situation.
Skewed data
One weakness of IJzendoorn's study is that 15 out of 32 of the studies were conducted in the US, therefore it is not representative of all the countries.
Not globally representative
One weakness of IJzendoorn's study is that they didn't include any countries from Africa, South America or Eastern Europe and that they only studied western-oriented countries.
Not necessarily cross-cultural variation

One weakness of IJzendoorn's study is that they only studied variation between different countries. They ignore the fact that many of the countries have similar cultures and the variety of cultures within countries themselves.
