The Malmö Diet and Cancer Study: representativity, cancer incidence and mortality in participants and non-participants.
In order to investigate potential selection bias in population-based cohort studies, participants (n = 28098) and non-participants (n = 40807) in the Malmö Diet and Cancer Study (MDCS) were compared with regard to cancer incidence and mortality. MDCS participants were also compared with participants in a mailed health survey with regard to subjective health, socio-demographic characteristics and lifestyle. Cancer incidence prior to recruitment was lower in non-participants, Cox proportional hazards analysis yielded a relative risk (RR) with a 95% confidence interval of 0.95 (0.90-1.00), compared with participants. During recruitment, cancer incidence was higher in non-participants, RR: 1.08 (1.01-1.17). Mortality was higher in non-participants both during, 3.55 (3.13-4.03), and following the recruitment period, 2.21 (2.03-2.41). The proportion reporting good health was higher in the MDCS than in the mailed health survey (where 74.6% participated), but the socio-demographic structure was similar. We conclude that mortality is higher in non-participants than in participants during recruitment and follow-up. It is also suggested that non-participants may have a lower cancer incidence prior to recruitment but a higher incidence during the recruitment period.
Manjer
J
J
Department of Community Medicine, Lund University, Malmö University Hospital, Sweden.
Carlsson
S
S
Elmståhl
S
S
Gullberg
B
B
Janzon
L
L
Lindström
M
M
Mattisson
I
I
Berglund
G
G
D000328:Adult; D000368:Aged; D002423:Cause of Death; D004032:Diet; D005260:Female; D005500:Follow-Up Studies; D006304:Health Status; D006306:Health Surveys; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009026:Mortality; D009369:Neoplasms / Q000453:epidemiology*; D018579:Patient Selection; D016016:Proportional Hazards Models; D011446:Prospective Studies; D015983:Selection Bias; D012959:Socioeconomic Factors; D013548:Sweden / Q000453:epidemiology