Scores were calculated as means of completed items.
It consisted of reviewing the completed items for validation.
Full model results available from authors Item non-response was examined by calculating the average percentage of items completed, and the percentage of respondents who completed all relevant questions, i.e. whether the percentage of items completed = 100% (Table 7).
Data completeness was measured by computing the percentage of items completed for each scale and the instrument.
Overall, the online mode shows the lowest average percentage of items completed, with almost 89% of questions answered compared to around 92% for each of the other modes.
The simultaneous mixed mode was more likely to have a higher percentage of items completed than the online in the 'About You' and 'Family' sections.
The sequential mixed mode was more likely to have a higher percentage of items completed than the online for the sections on DCE, workload, and location.
This is the case for all sub-sections of the survey, with the section on finances, which includes income questions, having the lowest average percentage of items completed of 80%.
The acceptability was tested by studying the percentage of refusals, the percentage of missing items, the percentage of complete questionnaires, the time taken to complete the questionnaire, as well as the acceptability questionnaire, which comprises the percentage of disturbing items, items that were hard to understand or confusing, and the willingness to fill out the questionnaire a second time.
According to the authors of the NKAS [ 30], the instrument is found to be most useful for analysing the data in terms of the percentage of complete scores as well as analyses of individual items.
