No, it’s absolutely not just due to low IQ - PIAAC did not control for cognative or linguistic difficulties with completing the survey beyond the strict inability to complete the background information (“Name” “Date” style of questions), which even true illiterate people are generally able to recognize through exposure. The study does not make conclusions about it, but it seems reasonable to confirm that the population of non-starters and <Level 1 participants (who made up approx 1/50 of the total US population at the time) would consist of people with very low IQs and all other potential difficulties with completing the survey, such as learning disabilities, dyslexia, language barriers, etc. both of a severity that they could not engage at all and less severe, meaning they could engage very minimally but enough to still be included as a participant.
(The rates at which that was the case are outside the scope of the study though they do propose several reasons for people being unable to participate, but could be looked into country-by-country if you’re curious)
No, it’s absolutely not just due to low IQ - PIAAC did not control for cognative or linguistic difficulties with completing the survey beyond the strict inability to complete the background information (“Name” “Date” style of questions), which even true illiterate people are generally able to recognize through exposure. The study does not make conclusions about it, but it seems reasonable to confirm that the population of non-starters and <Level 1 participants (who made up approx 1/50 of the total US population at the time) would consist of people with very low IQs and all other potential difficulties with completing the survey, such as learning disabilities, dyslexia, language barriers, etc. both of a severity that they could not engage at all and less severe, meaning they could engage very minimally but enough to still be included as a participant.
(The rates at which that was the case are outside the scope of the study though they do propose several reasons for people being unable to participate, but could be looked into country-by-country if you’re curious)