The sampling frame
The covert or disclosed nature of data collection, as this can substantially change what data can be collected around counters and clerks
Who is collecting the data, e.g., students, community members, or professional auditors
The reliability of measures, particularly novel survey items and items involving spatial estimation or physical measurement
If data collectors are blinded to tests of reliability or are aware they are participating in a reliability test
The wording and/or definition of items used as key variables in analyses, as elegantly done by Cohen et al, Feighery et al, and Lovato et al;[34, 40, 60] these can be operationalized in multiple ways (e.g., is snus measured as an emerging product or a smokeless product?)
The mode of the survey, as iPads™, iPhones™, or other electronic data collection devices can influence interactions with retailers and may have instrumentation effects
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