Condition category
Nutritional, Metabolic, Endocrine
Date applied
Date assigned
Last edited
Retrospectively registered
Overall trial status
Recruitment status
No longer recruiting
Publication status
Results overdue

Plain English Summary

Background and study aims
Non-response is an important issue for studies using a written questionnaire. For different reasons, potential participants are reluctant to complete questionnaires. Our aim is to find the best possible level of incentive (when using a written questionnaire and additional telephone interview) to participate in a study.

Who can participate?
Patients with diabetes who are aged 18 years or over can participate in this study.

What does the study involve?
Patients are randomly allocated to one of four groups. Patients are offered four different levels of incentive (either 5, 7.50, 10 or 12.50 euros, according to the group that they are allocated to) to participate in a written survey and an additional telephone interview.

What are the possible benefits and risks of participating?
All patients are part of the study, even if they do not participate (as we are studying the participation rate). The benefit for those who do participate is a gift card with a value of between 5 and 12.50 euros. There are no risks involved.

Where is the study run from?
This study is run from 7 GP practices; 5 of them in the city of Arnhem and 2 in the region ‘Achterhoek’ (including the towns Aalten and Gendringen), Netherlands.

When is study starting and how long is it expected to run for?
Recruitment of patients started in June 2013 and will last until August 2014.

Who is funding the study?
The study is funded by the European Union, Belgium.

Who is the main contact?
Mr Jan Koetsenruijter,
Professor Michel Wensing,

Trial website

Contact information



Primary contact

Prof Michel Wensing


Contact details

Geert Grooteplein 21
6500 HB

Additional identifiers

EudraCT number number

Protocol/serial number


Study information

Scientific title

The effect of different incentive levels on the participation rate for a mailed survey and telephone interview: a randomized controlled trial


Study hypothesis

Higher incentives will lead to a higher response rate, but this effect is not linear. For example, the relative increase of response will become smaller as the incentive becomes higher. Moreover, we expect this curve to be different between high and low deprivation areas.

Ethics approval

Committee on Research Involving Human Subjects (CMO) region Arnhem - Nijmegen (Commissie Mensgebonden Onderzoek [CMO] regio Arnhem – Nijmegen), 08/04/2013, ref: 2013/098

Study design

Randomized controlled trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting

GP practices

Trial type


Patient information sheet

Not available in web format, please contact to request a patient information sheet


Participation rate within patients with type 2 diabetes


Patients are randomized within a GP practice. At the GP practice the patient is handed over an anonymous and closed envelope with a specific level of incentive and a questionnaire included. Both researcher and the employee at the GP practice do not know the level of the included incentive.
Respondents are offered four different levels of incentive to participate in a written survey and an additional telephone interview. The incentives are 5, 7.50, 10 and 12.50 euros. This is the only difference between the four treatment arms. There is no follow-up planned.

Intervention type



Not Applicable

Drug names

Primary outcome measure

Participation rate will be studied within three different areas with different levels of deprivation (subgroup analysis). The participation rate is measured by the total amount of completed questionnaires and telephone interviews, divided by the total number of distributed questionnaires. This rate will be calculated for each level of incentive. There is only one time point as each participant can only complete the questionnaire once.

Secondary outcome measures

Not provided at time of registration

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Medical diagnosis of diabetes (not a patient-reported diagnosis)
2. Type 2 diabetes only (no type 1, but comorbidities such as cardiovascular disease are allowed)
3. Male and female, 18 years or over

Participant type


Age group




Target number of participants


Participant exclusion criteria

1. No established diagnosis of diabetes, but obesity or high risk for developing diabetes
2. Mix of type 2 and type 1 (not pure type 2 diabetes)
3. Pregnancy
4. Pregnancy-related diabetes
5. Recent/current major surgery or medical procedures
6. Severe cognitive or psychiatric handicap
7. Terminal illness/receiving palliative care
8. Absence of translators (e.g. family members) for patients with insufficient language skills

Recruitment start date


Recruitment end date



Countries of recruitment


Trial participating centre

Geert Grooteplein 21
6500 HB

Sponsor information


Radboud University Medical Centre (Netherlands)

Sponsor details

Postbus 9101
6500 HB

Sponsor type

Hospital/treatment centre



Funder type


Funder name

European Union (Belgium)

Alternative name(s)

Funding Body Type

Funding Body Subtype


Results and Publications

Publication and dissemination plan

Not provided at time of registration

Intention to publish date

Participant level data

Not provided at time of registration

Basic results (scientific)

Publication list

Publication citations

Additional files

Editorial Notes