Of the data set so far, we know the number of participants in 114 of the surveys. Three challenges have prevented knowing the participant numbers of the other 235 identified surveys. First, when no report has been published (or located by us), we often can’t know participant numbers from a press release or a reference to the survey in an article. Second, even when we have located a PDF of a published report, sometimes it does not provide that crucial fact of methodology. Third, we have not taken the time to extract from all the existing PDF reports their numbers of participants.
Extraordinarily, Osborne Clark Consumer 2018 obtained 16,000 participants. For this analysis and the associated plot, we have dropped that survey from the data set because otherwise its incredibly large response would skew the results.
The number of surveys for which participant numbers are available is low in the early years, but in the last decade the average number of participants hovers around the 250 mark. Over this entire set, the median number of participants is 210.
The plot with goldenrod columns divides all of the surveys for which we have participant data into 10 roughly equal ranges. They are equal because they have approximately the same number of surveys in each range, but the ranges themselves vary. To pick one for explanatory purposes, the range on the left, a dozen surveys collected data on 20-to-less-than-69 participants.