Schaffer and emerson - studied working class mothers and babies, observing them each month for the first year of the baby's life, and again at 18 months
- attachment was measured by looking at separation protest, eg when the infant was left alone AND stranger anxiety when the researcher approached the child, levels of distress were recorded
- found most infants started to show separation protest from their attachment figure between 6-9 months
- most infants went on to develop multiple attachments, at 18 months 87% of infants had at least two attachments