Recruitment Willingness to Pay

The sample for the online surveys were recruited via three routes:

A. direct approach to people who had completed a survey as part of Workstream 1 of this project (“wave 1”)
B. a sample purchased from the Pureprofile market research company (“pure”)
C. a sample recruited via publicity from support/patient groups (for example, Allergy UK, Coeliac UK, etc)(“support”).

Sample B was purchased – with respondents receiving remuneration via the market research company they are attached to.

As an inducement to recruitment, the emails and publicity material that generated samples A and C were offered the opportunity to be entered into a prize draw to win shopping vouchers.
The sample sizes achieved from the three recruitment routes are displayed in Table 8.1. As to whether the sample sizes are sufficient, we distinguish between statistical significance and representativeness of the results.

With only two attributes and a full factorial, orthogonal, experimental design the required sample sizes to retrieve statistically significant estimates are likely far smaller than those achieved.

A more challenging issue is that of the necessary sample size necessary to claim representativeness of the sample against the UK population of people with FHS. There are no reliable estimates of UK prevalence of the 3 FHS conditions included here, nor any breakdown of those populations in terms of condition severity or demographic characteristics. The strategy was to maximise the sample given timeframe and budget.

In conclusion, the challenge was not sufficient sample size to retrieve statistically significant estimates of the marginal utilities of the duration of FHS removal and the cost of that removal, rather the challenge was more generating sample sizes sufficiently large to have some confidence in generalising the estimated results. The sample sizes reported in Table 8.1 provide some confidence regarding representativeness, with the exception of children with Coeliac coeliac disease, an issue we return to in the discussion of the limitations of the study in Section 11.

Table 8.1: Samples sizes and sources, adult, children

Adults

Children