What is the ideal length of online questionnaires?

In recent years, the number of questionnaires, and in particular online questionnaires, has grown dramatically. Due to the fact that these questionnaires are self-administered and therefore without the support of an interviewer, the question arises as to the maximum duration that such a questionnaire must take in order to guarantee an adequate response rate.

The results of a recent study done in Germany and published in 2020 in the Journal of Market Research with two online panels (a probabilistic and a non-probabilistic panel) suggest that the ideal duration is between 10 and 15 minutes and the maximum duration is between 20 and 28 minutes depending on the measure of central tendency (mean or median) used on the panel. Significant differences were also found in these durations when taking into account demographic variables (gender, age, education and number of people in the household) and the ease in answering the questionnaire.