In this series I’ve been estimating a reader’s IQ using different methods, and now in part 3 we examine his psychometric history. Psychometric history is especially important in forensic cases where criminals may have faked their current low scores to avoid culpability, so they need to be corroborated by past scores.

The reader wrote:

My ‘reading level’ was assessed at 4th grade when I was in the 3rd grade, and 5th grade when I was in the 4th grade.

Unfortunately claims like this are ambiguous because “reading level” is not defined. Does reading at a 8th grade level mean reading like the average 8th grader? I don’t think so because even half of U.S. adults can’t read at an 8th grade level, so maybe these grade levels are relics from an era when only elites made it to high school.

The reader the provides a less ambiguous statement:

At 13 I was given a reading comprehension test and told that I was on the same level as the average college freshman.

Americans with “some college (13 -15 years of education)” have an average IQ of 102 (U.S. norms). Americans who graduate college (16+ years of education) have an average IQ of 111. College freshman eventually enter either of these categories so let’s split the difference and assume they have an average IQ of 107 (68 percentile).

Of course reading comprehension and IQ are not identical, but they are so highly correlated that we’d expect college freshman to be around the same percentile on both (for young adults).

If average college freshman reading skill is at the 68th percentile for young adults, what percentile is it at for 13-year-olds? I don’t have data on reading comprehension per se, but using vocabulary as a proxy, the WAIS-R and WISC-R manuals show that a vocabulary score that would put you between the 63rd to 75th percentile among 18 to 19-year-olds, would put you at the 95th to 98th percentile among 13-year-olds. So we might guess that the reader had a reading IQ of 128.

The reader also wrote:

The mean of my scores on Paul Cooijmans’ tests is 131. The median is, I believe, identical. My highest score is 148 and my lowest is 118 (excluding one spatial test on which my raw score was 0).

A raw score of 0 on Cooijman’s spatial test probably equates to an IQ of 103 or less.

The reader states:

My US Mensa ‘pretest’ score was 120. This was the first I.Q. test that I took as an adult. My [redacted by pp, 2021-04-14] score was 130 (137 verbal, 118 performance). I won’t mention any other online tests because they probably aren’t even remotely credible.

I redacted the name of one of the test’s he took because in my opinion, that test gives people too much exposure to the type of content on professional tests, and thus could compromise them.

So it looks like on credible tests, his scores range from 103 or less, all the way up to 148. Assuming his highest and lowest score were on tests that correlate about 0.7 (typical correlation between different IQ tests), 128 is what his real IQ is likely to be. Perhaps lower, since his lowest score suffered from floor bumping, but not much lower since his lowest score was an outlier.