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Gambling participation and the prevalence of problem gambling survey: Experimental statistics stage

Gambling Commission report produced by NatCen on the experimental statistics stage of the gambling participation and the prevalence of problem gambling survey.


In the pilot study, up to two individuals per household were invited to take part. The minimum age for participation was 16 years of age in order to maintain consistency with the Health Survey for England (HSE). As only eight individuals aged 16 or 17 years took part in the pilot, a recommendation was made to increase the minimum age to 18 years of age for the experimental stage.

Results from the pilot suggested that within responding households, those who gambled were more likely to take part than those who did not gamble, possibly due to the salience of the survey topic (that is because the survey is about gambling, it is disproportionately attractive to those who gamble).

A further source of suspected non-response bias towards those who gambled related to household participation having been restricted to a maximum of two adults, potentially creating a within-household selection bias whereby those most interested in gambling took part.

A recommendation was made to undertake further work to better understand this suspected non-response bias and make changes to attempt to reduce it. This section provides results from a methodological experiment, conducted in step 1, which investigated whether asking up to four, rather than two, adults in a household would reduce the potential for within-household selection bias (and capture more of those who did not gamble).

Issued addresses were randomly allocated to one of two experimental conditions. In the first experimental condition, up to two adults per household were invited to complete the survey. This was the method used for the pilot but in an attempt to reduce selection bias and improve random selection, instructions were added to the invitation letter stating that where the household contained three or more adults, the two adults with the most recent birthdays should complete the survey. This group is referred to as ‘C1 (up to two adults)’ in this report.

In the second experimental condition group, up to four adults per household were asked to complete the survey. No participant selection instructions were given so if the household contained five or more eligible adults, any four could take part. This group is referred to as ‘C2 (up to four adults)’ in this report.

The analysis looked to establish whether there were significant differences between the two experimental conditions which could reduce survey data quality, impact key survey statistics and contribute towards selection bias. Hence, the analysis carried out looked at whether there were differences between the two conditions in terms of:

  • completion rates in responding households
  • adherence to participant-selection instructions
  • rates of duplicate cases
  • rates of in-household clustering of gambling behaviours
  • the prevalence of certain gambling behaviours (gambling participation and problem gambling).
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Completion rates in responding households
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