Validity of self-reported utilization of physician services: a population study

Background: Health care utilization is of central interest in epidemiology, and most of the studies rely on self-report. The objectives of this study were to assess the validity of self-reported utilization of general practitioner and specialist physician by correlating self-reported utilization with registered services utilization, and to determine the factors related to that validity. Methods: The 1997 Belgian National Health Interview Survey (BNHIS) was linked with registered medical utilization data provided by the Belgian Health Insurance Funds. Valid information on general practitioner and specialist physician utilization during the past 2 months was found for 5869 participants at the BNHIS who were aged epsilon 25 years. Intra-class correlation coefficients were used to determine the rate of agreement, and multinomial logistic regression to model factors influencing under- and over-reporting. Results: The results demonstrated a substantial agreement between the self-reported and registered general practitioner contacts, and only a minor bias was found towards under-reporting. There was no significant difference between mean self-reported and registered specialist physician utilization, but the agreement was rather moderate. Gender, age, country of birth, self-rated health, number of chronic illnesses, having functional limitations and having mental health problems, were associated with under- and/or over-reporting. Conclusion: Studies that aim to compare the utilization of different socio-demographic groups have to take into account that the reporting errors vary by respondents characteristics.