Barrett suggests that the Protest-Despair-Detachment (PDD) model of separation response is outdated and proposes a more complex model for categorisation of separation anxiety.

Barrett argues that the evidence for PDD was never substantiated. Most evidence was from brief and anecdotal accounts of separations due to hospitalisation of the primary care giver and many of these accounts did not conform to the model well. In particular, the despair phase was rarely documented. In contrast, there is ample evidence for different accounts of separation responses. Reexamination of early films by Robertson (1950’s and 1967-1973) suggest that it is other factors (disruption of expected routine) that play a major part in separation anxiety, rather than a person-to-person attachment.  Also, the results of the strange situation procedure used by Ainsworth and Wittig (1969) showed a diverse range of reactions with large individual differences.  “Few workers familiar with research would now consider one pattern sufficient to describe separation responses in young children.'

Adult mourning shows different phases to the PDD model. The phase of Denial/Disbelief which is common in adult mourning is not catered for in the existing model and separation behaviour of married couples has been shown to differ markedly according to the circumstance of the separation.

She argues he simple PDD model is based on a outdated model of the young child. It is known known that distinctive individual styles of coping are evident early in infancy.  More modern social interactionist and constructivist models of child development would suggest a greater contribution of individual difference and environmental factors to separation behaviour than learnt PDD patterning.