Wherein lies the truth? Assessment of agreement between parent proxy and child respondents.

BACKGROUND: The epidemiological study of diseases of childhood presents a special situation in that the principal respondent is almost always a person other than the index. Use of proxy respondents in paediatric epidemiology has been little studied compared with the use of surrogate respondents for adults.
METHODS: Agreement between responses from children and their parents to identical questions about the children was assessed in a case-control study of childhood melanoma in Queensland, Australia. Weighted kappa and log-linear modelling techniques were used to measure agreement for ordinal data.
RESULTS: Highest agreement was found for reports of unchanging physical characteristics such as eye colour (kappa = 0.88), hair colour (kappa = 0.76), and for history of residing on a farm (kappa = 0.84). Moderate agreement was seen for density of facial freckling (kappa = 0.62), propensity to sunburn (kappa = 0.46) and tanning ability (kappa = 0.47). Variables with low levels of agreement between parent proxy and child respondents included density of freckling on the shoulders (kappa = 0.28) and degree of moliness of the skin at age 5 years (kappa = 0.24). Agreement did not vary according to age or sex of the children. Log-linear modelling was performed to determine the type and magnitude of components of agreement.
CONCLUSIONS: Agreement between responses from children and parent proxies depends largely upon the type of information sought, rather than characteristics of the respondents.