Table 2

 Summary of methods of studies included in analysis

Trial name or location, and year of trial startMethods
Göteborg, Sweden 196319Included all men born in 1913 and living in Göteborg, Sweden, in 1962. Allocation of participants was done according to date of birth before any contact was made. The intervention group was invited for 3 rounds of health checks, and the control group was not contacted. All were followed through registries for mortality.
Kaiser Permanente, USA 196526In April 1964, a sample of eligible members of the Kaiser-Permanente Health Plan in San Francisco and Oakland was divided into an intervention group and a control group using an allocation rule based on membership number. Starting in 1965, people in the intervention group were urged annually, by telephone and letter, to have the multiphasic screening examination offered by the Kaiser Health Plan. The intervention was continued for 16 years. Participants were followed using mailed questionnaires, patient records, and registers.
South east London, UK 196714Eligible people were identified through GP registers and randomised by family to intervention or control by alternate allocation of alphabetically ordered names. The intervention group was invited by letter to two rounds of health checks, with a two year interval. After five years, both groups were invited for health checks and measurement of some outcomes. A later publication state that this screening was not expected to result in therapeutic activity. Follow-up was continued for a further four years through records and registers.
Northumberland, UK 196915All eligible men were allocated at the same time before any contact was made, excluding 7% because of serious illness. Participants were allocated by date of birth to one of three groups: questionnaire and full examination, questionnaire and examination if indicated by answers to the questionnaire, and neither questionnaire nor examination. We used the first and the last group in our analyses. Outcomes were assessed from medical records.
Malmö, Sweden 196920Included all men born in 1914 and living in Malmö, Sweden, in early 1969. Men born in even-numbered months were invited to screening, and men born in uneven-numbered months were not. Outcomes were ascertained through registers.
Stockholm, Sweden 196921A double sample was drawn from the eligible population and divided into three age groups. From these, a random sample was drawn using sample fractions in the proportions of 3:2:1, with the highest fraction for the youngest age stratum. These were sent a questionnaire about social and physical difficulties and health needs. Based on this, and on data from the public inpatient register, they were substratified by expected needs for medical services (high, low, none, and unknown need). Randomisation to screening and control groups took place within these strata, but proportionally more were randomised to screening in the high and low need groups than in the no or unknown need groups. The authors used regression analysis to control for baseline imbalances introduced by the randomisation scheme and age and sex. We obtained data from the authors and conducted a fixed effects meta-analysis of the effects obtained in each stratum, and found nearly identical results to those of authors. Results from this analysis were used in the meta-analysis. Participants were followed for mortality in registers.
Göteborg, Sweden 197022Included men in Göteborg who were born in 1915–22 and in 1924–25. These were randomised to an intervention group and two control groups. They were followed in registers for mortality and morbidity.
WHO, Europe 197127Forty matched pairs of factories in four European countries (UK, Belgium, Poland, and Italy) were randomised to intervention or control. Follow-up varied between factories, but was between 5 and 6 years. Cancer mortality was not ascertained in the Belgian part of the trial.
Salt Lake City, USA 197223Included random samples of low and middle income families, both with and without prepaid healthcare. Randomised by family. Allocation ratio was 3:2 (intervention:control). Intervention group was urged by telephone to have a free health check. Outcomes were ascertained at interview after one year.
Mankato, USA 198224Addresses representing the entire community were randomised. In the intervention group, the whole household was invited for screening, but only one eligible participant from each household, selected randomly, was included in the trial and followed. The control group was not invited. After one year, participants in the intervention group who attended the initial screening were re-invited, and the control group was invited for their first time.
OXCHECK, UK 198916Eligible people who returned an initial questionnaire were included and randomised by household into four groups: health checks at year 1 and 4; at year 2 and 4; at year 3 and 4; and only at year 4. Participants in the first two groups were further randomised to annual re-checks or no re-checks. We regarded the first three groups as the intervention group and the last group as the control group. We obtained data on mortality and cancer incidence from the authors.
Family heart, UK 199017Thirteen matched pairs of general practices were randomised to intervention or control (external control group). In the intervention practices, eligible men were randomised to either intervention or control (internal control group), and their partners were included. The intervention group was invited for health check and lifestyle intervention at baseline. After one year both intervention and control groups were invited. Only those participants who attended their first health check were included in the analyses (that is, at baseline for intervention group and after one year for control group).
Ebeltoft, Denmark 199218A random sample of 2000 was taken from the eligible population of 3464. The sample was sent a short questionnaire, and participants returning the questionnaire and giving consent (n=1507) were included and randomised into three groups: offered health checks (n=502), offered health checks plus health discussions (n=504), and usual care (n=501). Participants were followed in registers for eight years, and comparisons were made between (a) the three intervention groups and (b) the 2000 randomly invited to participate in the trial (plus 30 in whom invitation failed for administrative reasons) and the 1434 not invited. We preferentially used the results from the second comparison.
Inter99, Denmark 199925All 61 301 people aged 30, 35, 40, 45, 50, 55, and 60 years and living in 11 municipalities in the south western part of Copenhagen County on 2 December 1998 were included. A random sample was invited to screening, and the rest constituted the control group. The intervention group and a random subsample of the control group had questionnaires at baseline and after 1, 3, and 5 years of follow-up. All participants were followed up through central registers. Results on morbidity and mortality are not yet published.