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Table 1 Summary of the 116 included studies - study designs and level of evidence

From: Reaching the hard-to-reach: a systematic review of strategies for improving health and medical research with socially disadvantaged groups

Level of evidence Study type N of studies Reference
Good Randomised controlled trial (RCT) 9 [23, 24, 36, 37, 42, 43, 88, 90],[106]
Fair Non-RCT comparison of strategies or groups 14 [17, 25, 41, 59, 61, 62, 79, 83],[104, 109, 110, 116, 126, 128]
Poor Descriptive study (with quantitative data, e.g., % of target group recruited, often single strategy pre-post)# 48 [1416, 1822],[26, 27, 30, 33, 35, 3840],[4447, 4951, 53],[54, 58, 6567];[71, 75, 76];[77], [81, 84, 85, 87, 91, 9597],[99, 112, 113, 117, 119, 120, 125, 129]
Poor Qualitative study (e.g., focus groups or interviews) 16 [29, 32, 60, 64, 68, 72, 73, 86],[89, 92, 94, 101, 108, 122, 124, 127]
Poor Case studies without data 28 [28, 31, 34, 48, 52, 5557, 63, 69],[74, 78, 80, 82, 93, 98, 100, 102],[103, 105, 107, 111, 114, 115, 118, 121],[123]
  1. #Descriptive studies are observational, with no comparisons made but data is reported (either increasing sample size, response rate, representativeness or acceptability).