Table 4.

Summary of the results from ‘ sampling ’ studies included in the review (n = 33 studies)

Barriers	Strategies
Difficult to locate or reach and access groups (e.g., homeless people living on the streets)	• Snowball/social network or respondent-driven recruitment [33,57,60,62,79,84,102-104,116],[118,126,129]
Frequent change of address or self-identifying, (e.g. GLBT) results in no sampling frame.	• Time-space sampling [38,104,113]
	• Targeted sampling [34,79]
	• Capture-recapture [95]
	• Adaptive sampling [53]
	• Partnerships with community groups [32,40,44,47,54,60-62,67,74],[103,116,118,122,128]
Low prevalence in population (e.g., Aboriginal people).	• Combination of various data sources as a novel methodology to avoid sampling [62,97] or supplementing with additional data (e.g. from qualitative research) [44,47,54,60,67,103,113,122],[128]
	• Statistical analysis techniques to population survey data for low-frequency samples [91]
	• Internet samples [51]