The parents of each child were asked to complete the survey questionnaire in self-completion format.
All Boost participants were asked the questions in the self-completion format.
We might expect this because those with poor reading skills may be put off by the self-completion format.
Otherwise HSE questions were converted to self-completion format with the aim of keeping the question wording as similar as possible to the HSE interview.
Finally, the GHQ12 and social support modules were asked in identical self-completion format in both the Core and Boost surveys, yet had different results, though these were small for social support.
The amount of filtering used in the CAPI was much too complex for a self-completion format, so Boost participants were provided with a list of the same 10 activities (and space to add up to three extra).
Similarly, their levels of fruit and vegetable consumption is likely to be higher as there is a greater temptation in the self-completion format to include consumption that falls outside the one-day period covered in the questionnaire.
The complexity of the filtering for these modules meant that the self-completion format used for the Boost results in much higher levels of missing data, so that when complex variables are derived combining responses to many questions, the level of missing information is much higher for Boost than Core respondents (as there is very little missing data in a CAPI interview).
Questions about perceived social support the General Health Questionnaire (GHQ) 12, an indicator of psychological health, in which twelve questions are used to assess the participant's present state relative to their usual, or normal, state [ 13], were both asked in a self-completion format.
A recent review identified six commonly used questionnaires and concluded that the measures differ substantially in a number of aspects (conceptual and measurement model, reliability, validity, interpretability, burden of completion, administration format, validated translations) [ 6].
