IQ 78
What does an IQ of 78 mean?
78 is near the top of the Borderline band, 1 point below the Low Average line at 80. Here is what the score means, how rare it is, and how close it is to the next label.
Short answer
An IQ of 78 is well below average. It is higher than about 7.1% of people, which puts it at the 7.1 percentile. About 1 in 14 people score 78 or lower, and the WAIS-IV labels it Borderline (70 to 79). It is 1.47 standard deviations below the mean of 100.
Specimen · IQ 78
78IQ
- Classification
- Borderline
- Percentile
- 7.1
- Rarity
- 1 in 14
- z-score
- −1.47
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| Percentile | 7.1 |
| Share scoring 78 or lower | 7.1% (about 1 in 14) |
| Out of 1,000 people | about 71 at or below |
| Standard deviations from the mean (z) | -1.47 |
| WAIS-IV classification | Borderline (70 to 79) |
| Same percentile, SD 16 scale | 77 |
| Same percentile, SD 24 scale | 65 |
What an IQ of 78 means on the scale
Modern IQ tests report a deviation IQ: scores are standardized so the mean is 100 and the standard deviation is 15 within each age group (Wikipedia: Intelligence quotient). On that scale 78 is 1.47 standard deviations below the mean. It is outside the 85 to 115 range that holds about 68% of people, but inside the 70 to 130 range that holds about 95%. (the 68-95-99.7 rule)
In a room of 30 people your age, about 2 would be expected to score 78 or lower. Put another way, about 93 out of every 100 people score above 78.
The Borderline band: 70 to 79
The WAIS-IV uses the label Borderline for scores from 70 to 79 (Wikipedia: IQ classification), between about one and a third and two standard deviations below the mean. About 6.5% of people score in this range.
The label names a score range on one test. It is not a diagnosis, and on a short online test it is not even a reliable placement: tiredness, an unfamiliar format, a small screen or simply not taking the test seriously can each pull a score into this range. 78 is 9 points above the line at 70 that separates this band from the lowest one.
Where 78 sits inside the band
78 is 8 points above the floor of the Borderline band (70) and 1 point below its ceiling (79). Of the people who score in this band, about 71% score below 78, so it is near the top of the group that shares its label.
Clinical IQ scores carry measurement error of around plus or minus 5 points at 95% (Wechsler, 2008). A measured 78 is consistent with a true score anywhere from 73 to 83, which is the 3.6 to 12.9 percentile. That range spans two labels, Borderline and Low Average, so the band name is the least certain part of the result. A short online test has a wider range than a clinical one, so read any single number as the middle of a span.
What an IQ of 78 does and does not predict
If a careful, supervised test produces a score in this range, it can help explain why some kinds of tasks feel harder. It does not define what a person can do, learn or become.
Across large groups, the links are real. General intelligence at age 11 correlated 0.81 with exam results at 16 in about 70,000 English children (Deary, Strand, Smith & Fernandes, 2007), a review of 85 years of workplace research put the link with job performance at 0.51 (Schmidt & Hunter, 1998), and a 2007 meta-analysis found correlations of about 0.56 with education and 0.23 with income (Strenze, 2007). Those describe tendencies across many people. None of them let anyone predict an individual life from one number. The guide to what IQ predicts explains what a correlation of that size means.
Same score, different tests
Older Stanford-Binet forms used a standard deviation of 16, and the Cattell Culture Fair III scale uses 24 (Wikipedia: IQ classification). The same percentile as 78 on a standard-deviation-15 test reads as about 77 on the first and 65 on the second, so check which scale a number is on before comparing scores from different tests.
Nearby scores
| IQ | Percentile | Rarity | Classification |
|---|---|---|---|
| IQ 70 | 2.3 | 1 in 44 | Borderline |
| IQ 75 | 4.8 | 1 in 21 | Borderline |
| IQ 76 | 5.5 | 1 in 18 | Borderline |
| IQ 77 | 6.3 | 1 in 16 | Borderline |
| IQ 79 | 8.1 | 1 in 12 | Borderline |
| IQ 80 | 9.1 | 1 in 11 | Low Average |
| IQ 81 | 10.3 | 1 in 10 | Low Average |
| IQ 85 | 15.9 | 1 in 6 | Low Average |
| IQ 90 | 25.2 | 1 in 4 | Average |
IQ 77 · IQ 79 · every score on the IQ chart · IQ percentile calculator · the seven classification bands
Sources
- Intelligence quotient. Wikipedia. en.wikipedia.org/wiki/Intelligence_quotient
- IQ classification. Wikipedia. en.wikipedia.org/wiki/IQ_classification
- 68-95-99.7 rule. Wikipedia. en.wikipedia.org/wiki/68%E2%80%9395%E2%80%9399.7_rule
- Wechsler, D. (2008). WAIS-IV Technical and Interpretive Manual. Pearson.
- Deary, I. J., Strand, S., Smith, P., & Fernandes, C. (2007). Intelligence, 35(1), 13-21. doi.org/10.1016/j.intell.2006.02.001
- Schmidt, F. L., & Hunter, J. E. (1998). Psychological Bulletin, 124(2), 262-274. doi.org/10.1037/0033-2909.124.2.262
- Strenze, T. (2007). Intelligence, 35(5), 401-426. doi.org/10.1016/j.intell.2006.09.004