Estimation of outpatient risk characteristics and influenza vaccination status: Validation of a self-administered questionnaire

As part of an effort to evaluate the effectiveness of a multifaceted, institution-wide influenza vaccination program, we mailed a self-administered postcard questionnaire to 500 randomly selected outpatients following both the 1987-1988 and 1988-1989 immunization seasons. The postcard asked if the patients received influenza vaccine, where they were immunized, whether they had any high-risk medical illnesses, their age at their last birthday, and their name. To assess the validity of the questionnaire, following the 1988 survey, we selected a 25% systematic sample of respondents and compared survey responses with medical record documentation. Response rates for the surveys were 77.6% for the 1988 survey (two mailings) and 86.5% for the 1989 survey (three mailings). Ninety-four percent (n = 89) of charts selected for audit were successfully reviewed. Agreement between questionnaire responses and medical records was excellent, with greater than 90% agreement and kappas of .8 to .9 for classifying patients as high-risk and receipt of vaccine at the Department of Veterans' Affairs Medical Center. For other data, agreement ranged from 84% to 96% with kappas of .6 to .75. Responses to the 1989 survey also demonstrated the importance of sample frame definition and response wave on estimates of risk characteristics and vaccination rates. A self- administered postcard questionnaire is a valid tool for estimating outpatient risk characteristics and influenza vaccination rates.