The paper mentions a similar issue: > Beyond inconsistencies in demographics across the sample, another factor that could be accounting for lower scores for mo

The paper mentions a similar issue: > Beyond inconsistencies in demographics across the sample, another factor that could be accounting for lower scores for more recent participants could be due to a decline in motivation. As the SAPA Project is advertised as a personality survey, individuals seeking out the SAPA Project may not be fully engaged with items not measuring temperament at the capacity as they are with more typically considered personality items. A bigger issue to me is > it should also be recognized that the SAPA Project relies on participants finding or seeking out the survey; meaning members of the population do not have an equal probability of being recruited into the survey (Condon, 2018). Thus, selection bias has likely been introduced into the sample due to those voluntarily taking the survey being non-representative of the target population I could see the result simply showing that the Internet (and/or college) has become more accessible since 2006 and sampling the online population reflects this. If we did online IQ tests starting the in late 80s, I'd imagine we would see a bigger downward trend during the 90s. On the other hand, King of the Hill was making fun of online IQ tests in 2002, so maybe they wouldn't be so hard to access.