A limitation is the impact of confounding variables. Studies conducted in different countries are usually not matched for methodology when they are compared in meta-analyses. Factors like poverty, age and social class and environmental factors like size of the room and availability of interesting toys can all confound results. for example, babies might appear to explore more in small rooms with attractive toys compared to large, bare rooms. This means that looking at attachment behaviour in non-matched studies conducted in different countries may not tell us anything about cross-cultural patterns of attachment.