It was a naturalistic observation. Behaviour was studied in the environment where it most naturally occurs. The parents observed and took notes on their infants responses to separation and strangers in their own home, during their normal routines. In addition to this, the researchers were not present at the time, so it is more likely that the infants behaviour would be more natural (unaffected by the presence of strangers). This is a strength as we can therefore say that the study has good external validity- results can be generalised to real life settings.
