Investigation of bias related to non-return of consent for a dental epidemiological survey of caries among five-year-olds

Estimates of caries levels derived from an epidemiological survey of five-year-olds in England were lower than expected. This survey used, for the first time, a consent method which involved parents providing positive, written consent for their child to be included in the survey. This contrasted to the previous method when negative consent was used. Aim: To interrogate the dataset to try and establish the reasons for the lower than expected estimates and explore the effect of non-return of parental consent, including the role of deprivation. Basic research design: Statistical analysis of an existing dataset and a sub-set of this dataset. Main outcome measures: Estimates of caries prevalence and severity in groups and sub-groups of a population-based, random sample of five-year-olds. Results: Hypotheses relating to possible changes in the process of data collection and analysis were rejected as reasons for the apparent reduction in disease estimates, as was the impact of oral and general health improvement programmes. Analysis of higher non-return levels on differences between past and current estimates and analysis of the associations between caries estimates, non-consent and summed deprivation measures based on home postcodes showed some relationships between these variables but could not identify a simple relationship. Conclusion: There is a more complex relationship between non-return of consent and disease levels than can be explained by deprivation alone.