A strength of the study that led to the stages of attachment is that it is high in ecological validity. The data was collected in the homes of the participants which means that the participants were likely to behave as they normally would rather than unnatural behaviours.
If this research was to be conducted in laboratory settings, infants may have not shown the same dehaviours due to the unusual environment. This is a strength because we can trust that the data collected was accurate.
What is a limitation of the methodology used in the study?
A final limitation of this theory is that it may suffer with culture bias as different societies have different childrearing practices. For this reason it cannot be assumed that children in every culture and every country in the world will move through these four stages in the same way as Schaffer and Emerson's participants. For example, Van Ijzendoorn (1993) found that those from collectivist cultures developed multiple attachments much earlier than this theory suggests due to their emphasis on being part of a group. This is limitation because the theory may lack generalisability.