Table 1 Descriptive statistics of the retrieved publications

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