Van IJzendoorn and Kroonenberg conducted a meta-analysis of various countries, including Japan, Israel, Germany, China, the UK and the USA using the Strange Situation. The research showed that though there were cultural differences, the four basic patterns, secure, avoidance, ambivalent, and disorganized can be found in every culture in which studies have been undertaken, even where communal sleeping arrangements are the norm. Selection of the secure pattern is found in the majority of children across cultures studied. This follows logically from the fact that attachment theory provides for infants to adapt to changes in the environment, selecting optimal behavioural strategies. How attachment is expressed shows cultural variations which need to be ascertained before studies can be undertaken.