Postal surveys of service use are likely to overestimate health service use
and may also underestimate health needs in the population. A historical co
hort study, using postal questionnaires and medical records, showed that no
n-respondents are registered at addresses in more-deprived wards, they are
less likely to have attended a hospital diabetes clinic (38% vs 45%) and mu
ch less likely to have had a diabetes review in general practice (11% vs 26
%). An analysis based on questionnaire respondents would only therefore bot
h underestimate the level of material deprivation and overestimate the prop
ortion receiving routine reviews in general practice in a population with a
chronic condition.