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Table 1 Descriptive statistics of the retrieved publications

From: Hard-to-reach populations of men who have sex with men and sex workers: a systematic review on sampling methods

Recruitment methods Number of studies Percent Total sample sizes Mean Median Minimum Maximum Study referencea
RDS 77 28.7 82,004 1065 496 50 18,960 [1–39] [40–77]
TLS 42 15.7 55,193 1346.2 526 200 16,270 [78–119]
Convenience 33 12.3 18,698 584.3 305.5 36 2569 [120–152]
Snowball 36 13.4 18,148 504.1 331.5 20 3314 [153–188]
Internet 33 12.3 225,320 6827.9 522 32 144,177 [189–221]
Targeted 15 5.6 6197 413.1 485 22 806 [222–236]
Purposive 6 2.2 195 32.5 26.5 17 58 [237–242]
Multi-stage probability sample 4 1.5 3175 793.8 216 121 2622 [243–246]
Cluster 3 1.1 1901 633.7 504 324 1073 [247–249]
Convenience, snowball 3 1.1 687 229 253 161 273 [250–252]
TLS, Internet 2 0.7 1167 583.5 583.5 566 601 [253, 254]
RDD 2 0.7 2659 1329.5 1329.5 879 1780 [255, 256]
Convenience, Internet 2 0.7 2291 1145.5 1145.5 770 1521 [257, 258]
Convenience, RDD 1 0.4 218      [259]
Convenience, RDS 1 0.4 624      [260]
Internet, snowball 1 0.4 1692      [261]
RDS, TLS 2 0.7 1853 926.5 926.5 737 1116 [262, 263]
Stratified probability sampling, Internet 1 0.4 2182      [264]
Targeted, snowball 1 0.4 48      [265]
Convenience, snowball, Internet 1 0.4 103      [266]
Snowball, TLS, RDS 1 0.4 1407      [267]
RDS, Internet 1 0.4 2147      [268]
Total 268 100 427,909      
  1. aReferences can be found in Additional file 4: Text S3