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Given the heterogeneity of designs, length of follow-up and outcome measurements of the available studies, pooling of selected results for a meta-analysis was feasible only for four RCTs reporting 12-month follow-up results.
The remaining eight studies were critically reviewed but not meta-analysed. Changes in means, and tests of heterogeneity between trials were calculated using random effects models.
Meta-analysis was conducted using NCSS software version 7. Sensitivity analysis by study quality was not deemed necessary as all four studies finally selected for meta-analysis had a quality score of 7 or 8 out of the possible 8 maximum score.
Our search did not identify unpublished replication studies of diabetes prevention in routine clinical practice.
Accordingly, we expected findings not to be significantly affected by publication bias. Of these, 18 studies were excluded because: their replications of lifestyle interventions were conducted in non-routine clinical settings e.
A further 6 studies were excluded because: the study compared results retrospectively with reference trials without conducting an intervention ; the intervention was confined to a diabetes education component only ; the intervention was telephone-based only and had not replicated components of the reference trials ; or they were either duplicates, companion or interim reports, of studies already selected.
Differences in presentation of results e. One study, with the largest sample size, could not be meta-analysed to estimate the effects of a lifestyle intervention, as both the medication and placebo arms received the lifestyle intervention.
The final set of 12 studies covered in this review included 7 randomised controlled trials including one cluster RCT, 3 before-after designs without a control group and two before-after designs with a control group Table 1. The studies were conducted in 8 OECD countries, and had sample sizes ranging from 58 to 3,304 median 311, with participant ages ranging from 20 to 79 years; six of the studies targeted middle-aged people only.
All interventions combined physical activity and dietary advice, two studies also included medication as part of the intervention, and all were delivered in routine clinical settings, such as specialist services or hospital outpatient clinics 5, general practitioner consulting rooms 5 or community health services 2.
The target groups were people at high risk, defined either by the presence of impaired glucose tolerance, severe obesity, or metabolic syndrome or some of its components.
Eight of these studies also included normoglycaemic patients and two replication studies included both subjects with and without diabetes and pre-diabetes.
Table 1 Classification of eligible studies by design, target population, outcomes and quality score 1990- Full size table Types of lifestyle interventions reported All studies included a combined lifestyle intervention but two eligible studies included a medication arm in addition to lifestyle.
Seven studies attempted replication of the reference trial approaches from either the U.
S DPP or the Finnish DPS with adaptation to routine clinical practice, mostly to cater for limitations in practitioner's time and health service budgets.
Modifications of interventions during the maintenance phase included intermittent support sessions, more economical versions of the resources given to participants, and multidisciplinary teams, either available on site or hired as an additional service.
For interventions delivered in a group-based modality, the maximum number of sessions per program was 16, as per the reference trial median of 6 sessions, but over a shorter period of time. Among the 5 studies reporting delivery of individual counselling sessions, the median number of individual counselling sessions was 13.