what are the methodological limitations of Schaffer's and Emerson's study?
. its an unrepresentable sample as all the participants were from the same district and social class
.child-rearing practises may differ between social class
.therefore results may not be generalized well to people from other classes.
.this threatens the external validity
.longitudinal studies are prone to attrition, which may leave an unrepresentable sample. this reduces the external validity of the findings