Evaluate Schaffer and Emerson's research (KEY STUDY)
STRENGTH: longitudinal study- long period of development observed, giving deeper insight into development of attachment. More depth and detail increases validity. Furthermore, uses qualitative data which gives more detail.
STRENGTH: high ecological validity- naturalistic observation, e.g. parents observed and took notes on infants responses to separation, strangers etc.. Researchers weren't present at the time, so infants behaviour would be more natural. However, low internal validity, because of bias in diary entry from parents
WEAKNESS: ungeneralisable- small sample of Glaswegian babies, mostly from middle class. Study ethnocentric so cannot generalise to other ethnicities and only used 1 social class so cannot be generalised to other social classes. E.g. middle class can afford nanny, so attachment may happen with nanny instead.