Representativeness of autistic samples in studies recruiting through social media

Abstract

Survey-based research with recruitment through online channels is a convenient way to obtain large samples and has recently been increasingly used in autism research. However, sampling from online channels may be associated with a high risk of sampling bias causing findings not to be generalizable to the autism population. Here we examined autism studies that have sampled on social media for markers of sampling bias. Most samples showed one or more indicators of sampling bias, in the form of reversed sex ratio, higher employment rates, higher education level, lower fraction of individuals with intellectual disability, and later age of diagnosis than would be expected when comparing with for example population study results from published research. Findings from many of the included studies are therefore difficult to generalize to the broader autism population. Suggestions for how research strategies may be adapted to address some of the problems are discussed. LAY SUMMARY: Online surveys offer a convenient way to recruit large numbers of participants for autism research. However, the resulting samples may not fully reflect the autism population. Here we investigated the samples of 36 autism studies that recruited participants online and found that the demographic composition tended to deviate from what has been reported about the autism population in previous research. The results may thus not be generalizable to autism in general.

Keywords: autism; online recruitment; sampling bias; selection bias.

FIGURE 1

Overview of the percentages of studies that reported each of the selected markers of sampling bias. This does not include studies that reported demographics in other ways, such as total years of education or percentage diagnosed as adults.

FIGURE 2

Distributions of sample characteristics for the five markers of sampling bias among the included studies that had reported each of them. Each point represents a single study. The boxes indicate the quartiles of the distributions. The thick blue lines indicate estimates of where the mean would be expected in the autism population in general, based on the literature (see main text for details). For college/university, a conservative estimate based on the general population is used. The expected mean age of diagnosis in the whole population is difficult to estimate from the literature. Five studies included proxy responses, for example, by a relative. Mean sample characteristics for these studies were calculated as the weighted average between the self‐reports and proxy‐reports and are highlighted as red squares