The first contact

Successful measures for participant activation in F2F studies

Surveys using face-to-face interviews are described in the literature as the “gold standard”. However, the high quality is associated with high costs compared to other survey methods, as each address has to be visited several times by the interviewer. How time-consuming contacting is also depends on the contact information available. While telephone numbers or e-mail addresses are usually available in addition to postal addresses in panel surveys, only addresses are usually available in initial surveys. The interviewer can only make contact on site and rarely meets mobile or working respondents in particular.

In order to reduce the accessibility rate and the selective error due to non-accessibility, infas has carried out pre-contacts in three large face-to-face studies in recent years: in a refreshment sample of the IAB-BAMF-SOEP survey of refugees, in a linking study as part of the National Educational Panel Study (NEPS) and in the first wave of “Daten. Deutschland. Digital” (DaLi). The three studies differ not only in their target group and the design of the main survey, but also in the pre-contacting. Different measures were used in each case to maximize feedback.

Pre-contacting in the IAB-BAMF SOEP survey of refugees

In the refreshment sample of the IAB-BAMF-SOEP survey commissioned by the SOEP team at the German Institute for Economic Research (DIW), Berlin, the Institute for Employment Research (IAB) and the Federal Office for Migration and Refugees (BAMF) in 2023, adult refugees from Ukraine (SUARE) and from the rest of the world (REF) were asked about their living conditions in Germany. The gross sample comprised n=29,072 addresses from the Central Register of Foreigners (AZR). For the preliminary contact, the target persons first received a letter with information about the study and a request to take part in a short online survey. In addition to questions about availability and the request to provide current contact details, a few initial questions were also asked. Alternatively, the target persons could also complete the questions on the enclosed paper questionnaire and send it back to infas in a postage-paid envelope. In the REF sub-sample, a prepaid incentive of 5 euros was enclosed with this initial letter. In addition, all target persons were notified of a postpaid incentive of 20 euros after participating in the main survey. To increase the pre-contact rate, a reminder was sent three weeks after the initial letter to all target persons who had not yet responded by this time. In the SUARE sub-sample, a second reminder was sent three weeks later.

Before the reminder was sent, 14.9% of the target persons in the REF sub-sample had already taken part in the short survey as part of the pre-contact. Of the people who received the reminder, a further 10.9 % then took part in the short survey, resulting in a total response rate of 24.2 %. In the SUARE sub-sample, the response rate before the first reminder was sent was 11.2%. Of the target persons who received the first reminder, a further 7.1 % took part in the short survey and of those who received the second reminder, a further 4.4 % took part. The overall response rate in the SUARE sub-sample was therefore 21.1%.

When comparing the two subsamples, it can be seen that the use of the prepaid incentive in the first letter in the REF subsample leads to a higher take-up rate afterwards and that the take-up rate after the first reminder was sent was also higher. The positive effect of the prepaid incentive appears to continue after the first reminder. In addition, the second reminder in the SUARE sub-sample also led to a substantial increase in response rate, even if, as expected, it decreased with each mailing. Thus, although the positive prepaid effect in the REF subsample could not be completely compensated for, the overall response rate of the SUARE subsample was raised to a similar level.

Pre-contacting in the NEPS linking study

The NEPS linking study commissioned by the Leibniz Institute for Educational Trajectories (LIfBi) includes competence tests in the areas of mathematics and science for children aged 6 to 10 years. It is based on a residents’ registration office sample with n=26,000 addresses. At the start of the survey, the parents of all target persons received a letter with information about the study and a request to complete the enclosed feedback form. Alternatively, the key data about the child and the contact details could also be entered in an online form. This preliminary contact was not only used to identify families willing to participate and to update contact details, but also for screening purposes. This was because the children had to fulfill specific requirements for participation in the study, not all of which were available at the time of sampling. In the initial letter, the families were promised a post-paid incentive of 10 euros following the main survey as well as a gift in kind for the child. To increase the pre-contact rate, a reminder was sent a few weeks after the initial letter to those families who had not yet responded. In addition, a second reminder letter was sent at the beginning of August announcing an increase in the postpaid incentive to EUR 50. This second reminder letter was accompanied by a prepaid incentive of EUR 5 for half of the cases. As neither the first nor the second reminder letter was sent to all families due to considerations regarding the quota sample to be realized, there were a total of five groups that received different combinations of measures to increase take-up.

Before the first reminder was sent, we received direct feedback from 9.5% of families from the pre-contact. Of the families who received the first reminder, another 4.0% then contacted us again. The proportion of responses after the second reminder depended on the prepaid incentive and the prior receipt of the first reminder. In the group that did not receive the first reminder, 11.5% of families reported back without a prepaid supplement and 17.8% with a prepaid supplement. In the group that had already received the first reminder, 7.9% of families without a prepaid supplement and 12.2% with a prepaid supplement responded. The overall response rate for the five groups was between 13.1 % (group 1: only reminder 1) and 25.6 % (group 3: only reminder 2 with prepaid insert).

A comparison of groups 1 and 2 shows that the increase in the postpaid incentive from EUR 10 to EUR 50 significantly increased responses. In addition, the inclusion of a prepaid incentive in reminder 2 also substantially increased responses (approx. 55% higher response rate when comparing groups 2 and 3 or 4 and 5). The comparison of groups 2 and 4 also shows that the first reminder (without a postpaid increase) in group 4 already reached the families that were easier to convince and that fewer additional families were won over by the second reminder. Overall, approximately the same total take-up was achieved in both groups. In group 5, on the other hand, the total utilization was slightly lower than in group 3, although similar mechanisms can be assumed here. The lower take-up rate after reminder 2 could be related to the fact that some families did not open the second reminder letter at all and therefore the positive prepaid effect was less effective than in group 3, where reminder 2 was the first letter after the first letter and no fatigue effect had yet occurred.

Pre-contacting in the DaLi study

The study “Data. Germany. Digital” (DaLi) commissioned by LIfBi included competence tests to find out how people in Germany handle and understand data and digital information. It is based on a residents’ registration office sample of n=34,924 people between the ages of 16 and 69 (group 1), n=3,000 between the ages of 10 and 15 (group 2) and n=25,000 between the ages of 11 and 12 (group 3).

At the start of the survey, all target persons (group 1) and their parents (groups 2 and 3) received a letter with information about the study and a request to complete the enclosed feedback form. Alternatively, key data and contact details could also be submitted online. The pre-contact was not only used to update the contact data and request desired contact times, but also for screening, as in the NEPS study. In the initial letter, the target persons or their parents were informed of a postpaid incentive of 50 euros following the main survey.

The reminder measures were designed differently depending on the tranche, field period and group. Approximately four to six weeks after the first letter, all target persons who had not responded by then received a reminder letter for pre-contact. This was followed three weeks later by a motivational New Year’s card for all unreached target persons from groups 1 to 3 (tranche 1) and group 3 (tranches 2 and 3). In group 3, tranche 1 also received a second reminder letter. In group 1, the target persons from tranches 1 to 3 also received a second reminder letter, and particularly low-reached cohorts received a third reminder letter (tranches 1 to 4). A prepaid experiment was also conducted in group 1: The target persons in tranches 2 and 4 received a prepaid incentive in the first reminder letter, while the target persons in tranches 1 and 3 only received their incentive with the second letter.
In the following, the feedback from the target persons in the three DaLi groups is considered separately in order to better understand the effects of the various reminder measures.

In Group 1, we received feedback from between 4.2% and 5.8% of adults before the first reminder was sent. Of those who received the first reminder, an additional 3.9% to 8.0% responded. There was a clear prepaid effect in variant 2 with 8.0 % feedback compared to 4.7 % (variant 3) and 3.0 % (variant 1), while variant 4 with 3.9 % feedback showed no prepaid effect. The proportion of responses after the second reminder mailing depended on the inclusion of the prepaid incentive. In variant 2, which already received the prepaid incentive in the first reminder, 6.4 % of adults responded. For those who did not receive a prepaid incentive with the first reminder, but did receive one with the second reminder, the responses were 4.5% (variant 3) and 2.7% (variant 1). After the third reminder mailing, the response rate also depended on the prepaid insert in the first reminder and the receipt of the second reminder. Of those who received a prepaid incentive and a second reminder with the first reminder, 4.7% (variant 2) responded, compared to 2.5% (variants 1 and 3). Those who received a prepaid incentive with the first reminder and no second reminder showed a response rate of 6.2% (variant 4). The overall response rate was between 13.1 % (variant 1: reminder 2 with prepaid insert and three further mailings) and 21.3 % (variant 2: reminder 1 with prepaid insert and two further mailings).

In group 2, we received feedback from between 6.8% and 7.0% of families before the first reminder was sent as part of the pre-contact process. After the first reminder was sent, an additional 11.5% responded in variant 2. In variant 1, the response rate after the first reminder was only 2.6%, but an additional 7.3% of the target persons were reached by sending a New Year’s card. The overall response rate was between 16.0 % (variant 1: 1 reminder and 1 New Year’s card) and 17.5 % (variant 2: only 1 reminder).

In group 3, between 1.3% and 6.7% of families were contacted before the first reminder was sent. Of those who received the first reminder, a further 4.4% to 5.6% responded. Of those who received little feedback before and after the first reminder (variant 2), a further 12.1% responded to the New Year’s card, compared to only 3.5% in variant 1. Of those who received a second reminder, 3.2 % responded. The overall response rate was between 17.1 % (variant 2: 1 reminder and 1 New Year’s card) and 17.7 % (variant 1: 2 reminders and 1 New Year’s card).

In general, it can be seen that the proportion of responses from children and young people (Group 2 and Group 3) before and after the first reminder, after the New Year’s card was sent out and also in the overall response rate tends to be higher than for adults (Group 1). A clear “catch-up effect” from sending the New Year’s card can be seen in group 2 and group 3 when the responses before and after the first reminder were lower. In addition, a prepaid effect can be seen for group 1 with the first reminder. This prepaid effect intensifies in the later reminders and shows that the positive influence of the prepaid incentive is not only limited to the immediate feedback, but also tends to have an effect on the subsequent mailings. In contrast, there was no effect of the prepaid insert with the second reminder.

Is pre-contacting worthwhile? And if so, how?

In general, it can be said that yes, pre-contacting helps, as it reduces the effort for interviewers on site and more contact information is subsequently available from the participants. With regard to the question of “How?”, all three studies show similar mechanisms for the effect of pre-contacting.
The use of reminders always leads to an increase in feedback. However, the effect decreases with each additional reminder. The only positive exception here is the sending of New Year’s cards in the DaLi study, which could be due to the completely different approach. Additional reminders also produce a “catch-up effect” in some sub-samples, which can relativize a low response rate at the beginning.

A similarly clear conclusion can be drawn regarding the use of prepaid incentives: Used early on, they have a clear positive effect on the response rate, whereas using them in later reminder campaigns is less effective. When a prepaid incentive is used in the initial letter or the first reminder, an “inheritance effect” can be seen in addition to an increase in immediate feedback, i.e. there are also higher feedback rates in subsequent reminder campaigns than in comparison groups without prepaid incentives. However, these positive effects decrease with each additional reminder campaign. It can be assumed that some target persons no longer open the letters after a certain point in time and the prepaid insert no longer has any effect. In the NEPS study, it was also observed that an increase in the postpaid incentive also noticeably increases the response rate for pre-contacting.

In order to maximize the response rate of a pre-contact, at least two reminders should be planned, one of which should be a special promotion in a different format if possible. In addition, if possible, a prepaid incentive should be used, ideally in the initial letter, but at the latest with the first reminder.

To read more:
The websites for the studies mentioned:
SOEP, NEPS, DaLi

This article was first published in Position dimension 14 “select” published.