limitation
Studies conducted in different countries are not usually matched for methodology when they are compared in meta-analyses.
Sample characteristics such as poverty, social class, and urban/rural make-up can confound results, as can the age of participants studied in different countries.
Environmental variables also differ. eg size of the room, availability of interesting toys — babies might appear to explore more in studies conducted in small rooms with attractive toys compared to large, bare rooms.
Less visible proximity-seeking because of room size might make a child more likely to be classified as avoidant.
This means looking at attachment behaviour in different non-matched studies conducted in different countries may not tell us anything about cross-cultural patterns of attachment.