Recruitment and Consent in an observational study.

OBJECTIVE: The study sought to explore the consent rate and associated potential bias across a cohort in a large longitudinal population based study. RESEARCH DESIGN: Data were taken from a study designed to examine the effects of the reintroduction of community water fluoridation on children's oral health over a five-year period. Children were recruited from a fluoridated and non-fluoridated area in Cumbria, referred to as Group 1 and Group 2. RESULTS: Data were available for 3138 individuals. The consent rate was 12.91 percentage points lower in Group 2 than Group 1 (95% CI -16.27 to -9.56, p⟨0.001). The population in Group 2 was more deprived (higher Index of Multiple Deprivation (IMD)) than Group 1 before consent was taken. Consent was not associated with deprivation in either group. CONCLUSION: The cohort appeared to be unaffected by IMD-related non-consent. However there was a difference in consent rate between the two groups. With the population in Group 1 being more deprived than Group 2, it will be important to incorporate these differences into the analysis at the end of this longitudinal study.

Emotional face processing deficit in schizophrenia: A replication study in a South African Xhosa population.

Schizophrenia is associated with a deficit in the recognition of negative emotions from facial expressions. The present study examined the universality of this finding by studying facial expression recognition in African Xhosa population. Forty-four Xhosa patients with schizophrenia and forty healthy controls were tested with a computerized task requiring rapid perceptual discrimination of matched positive (i.e. happy), negative (i.e. angry), and neutral faces. Patients were equally accurate as controls in recognizing happy faces but showed a marked impairment in recognition of angry faces. The impairment was particularly pronounced for high-intensity (open-mouth) angry faces. Patients also exhibited more false happy and angry responses to neutral faces than controls. No correlation between level of education or illness duration and emotion recognition was found but the deficit in the recognition of negative emotions was more pronounced in familial compared to non-familial cases of schizophrenia. These findings suggest that the deficit in the recognition of negative facial expressions may constitute a universal neurocognitive marker of schizophrenia.