Outcomes

The outcomes assessed in this trial are presented in Table 1.

Trial outcomes

H historic study arm

^aGroup 1 refers to the intervention group and group 2 refers to the control group

^bDif_{Follow-up-Baseline}: The mean increase or decrease in knowledge, attitude, and worry-score from baseline to follow-up will be estimated. Means will be compared between the two study arms

Informed choice will be evaluated based on the following primary outcomes: consistency of knowledge about CRC screening, attitudes towards CRC screening, and screening uptake [34].

Knowledge will be measured via questionnaire before and after intervention using a seven-item scale developed by the authors based on both a literature search and patient information needs as previously clarified in focus group interviews [25]. Post-intervention levels and changes from baseline to follow-up will be evaluated.

Screening attitudes will be estimated using the translated four-item attitudes scale, ranging from 4 to 28 points [34]. The scale has been translated into Danish from English with conventional forward-backward translation [35]. Attitudes will be assessed at baseline and at follow-up.

Data on screening uptake will be collected from the CRC screening program database. Citizens will be defined as having taken up CRC screening if they return a stool sample within three months (90 days) after the screening invitation has been sent out [36].

The 16-item decisional conflict scale [37] will be used to measure decisional conflict, i.e. uncertainty about making the right choice. It comprises five subscales, including the decisional support subscale and the (perceived) effectiveness of the decision subscale. Scores range from 0 to 100 and data are collected at follow-up.

Worry about CRC will be assessed using three items on worry about CRC. Two items assess worry and anxiety when considering CRC screening and one assesses worry about the result of a screening test. Items have also been developed by the authors based on literature searches [19, 20, 38–40]. Scores are in the range of 3–15. Assessments are made at baseline and follow-up.

Health literacy is a multidimensional measure of a person’s ability to access, understand, appraise, and apply information about healthcare, disease prevention, and health promotion [41]. It will be measured at baseline using the 16-item HLS-EU-Q16 scale [41].

The use of the decision aid will be measured among citizens receiving an invitation to use it. However, detailed process data will not be collected, since the primary aim of this trial is to investigate the effectiveness of having the decision aid provided, regardless of actually reading it. Usability and acceptability have been further assessed in the development phase of the decision aid [26].

Background data on participants’ sociodemographic and socioeconomic characteristics will be obtained from Statistics Denmark [42] by the end of the study period. These data are updated annually.

Lower educational attainment is defined according to the UNESCO classification of basic education as < 10 years of education [43].

Family income will be divided into three categories based on lower, middle, and upper tertiles of the dataset. Occupation is a categorical variable with the following six categories: Employed; Self-employed/chief executive; Unemployed/receiving benefits; Retired; Social welfare recipients; and Others. Marital status is dichotomized into two categories: married/cohabitant and single. Ethnicity will be a categorical variable with three categories: Danish; Western immigrant (Western Europe and North America); and non-Western immigrant (Table 1).

Three different questionnaires will be administered in this trial: the baseline (knowledge, seven items; attitudes, four items [34]; worry, three items; health literacy – HLS-EU-Q16, 16 items [41, 44]) and follow-up (knowledge; attitudes; worry; decisional conflict, 16 items [37]) questionnaires, and the questionnaire for the historic study arm participants (knowledge; attitudes; worry; health literacy; decisional conflict) (Fig. 2).

Schedule of enrolment, intervention, and assessments. Figure depicting the enrolment, intervention, and assessments according to SPIRIT 2013 statement [46]. ^§ Assessed only in the historic cohort. BD background data, obtained from Statistics Denmark. Follow-up occurs throughout a period of 12 weeks. The final data will be obtained from the screening program IT system when all follow-up data have been collected. The complete data will then be merged with background data from Statistics Denmark

All questionnaires will be administered via REDCap Software (Version 6.12.0 - © 2016 Vanderbilt University) [45]. Data entry will occur automatically when the citizens complete the electronic questionnaires, hence no manual data entry will be required. The questionnaires are presented in Additional files 1, 2 and 3.