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The recruitment of panel members was achieved via a first phase of push-to-web (Phase 1) and a second phase of face-to-face-interviewing (Phase 2).

Recruitment phase 1:

Postal mailing with invitation letter, information brochure, privacy brochure, and unconditional incentive (€5 gift voucher).

Invitation to join the panel and complete an online recruitment questionnaire.

Sampled persons received an additional cash incentive (€ 8,00 paid into the bank account) if they joined the panel.

If the sampled persons complete the questionnaire before the deadline of 18 days after receiving the first call, they get an early bird bonus of € 20,00.

In case of non-response on the first mailing, a reminder was sent in a second mailing 11 days after the first mailing.
This mailing included the same materials as the first mailing, but without the cash incentive.

Recruitment phase 2:

In case of non-response in recruitment phase 1, sampled persons were visited by an interviewer three weeks later.

The interviewer conducted a face-to-face recruitment interview using CAPI.

Intended to make sampled individuals become more familiar with the panel.

Sampling procedure

The panel is based on a probability sample drawn from The Belgian National Register of Natural Persons. To obtain the random sample, we employed a stratified, two-stage cluster design where boroughs (NIS6) were the primary sampling units, and residents the secondary sampling units.

At the first stage, 800 sampling points were randomly selected by a systematic random sampling procedure with replacement clustered within boroughs, explicitly stratified by regions and provinces and implicitly stratified by target population size. Sampling points corresponded to a fixed number of expected panelists (n = 5) and a varying number of gross sample persons, depending on expected response rates. We estimated expected response rates based on historic and current response rates achieved by several face-to-face, random-probability surveys of the general resident population in Belgium.*
Because response rates are typically lower in more urban areas, we oversampled based on urbanicity class of the borough (higher-order Belfius classification). This involved selecting larger (gross) sampling points in more urban areas and smaller ones in rural areas.

At the second stage, persons within the selected boroughs were randomly selected from the Belgian National Register by Statistics Belgium (Statbel). This was done using a systematic random sampling procedure without replacement and with equal inclusion probabilities, while implicitly stratified by age and sex.

The gross sample size is divided into three batches to optimize the practical organization of the fieldwork.