AO3 of Schaffer and Emerson
+ good external validity as carried out in the homes
+ longitudinal so good internal validity as children followed up so no confounding variables as same children used
- can't be generalised due to small sample
- only applies to working class Glasgow babies
- lacks temporal validity: 1960s Scotland had different social roles than it does today, so can't be applied to today's society
- doesn't necessarily measure attachment as stranger and separation anxiety are only two components that make up attachment