Editing G factor (psychometrics) (section)

==Population distribution==

The form of the population distribution of ''g'' is unknown, because ''g'' cannot be measured on a [[ratio scale]]{{clarify|date=March 2018}}. (The distributions of scores on typical IQ tests are roughly normal, but this is achieved by construction, i.e., by [[Normalization (statistics)|normalizing]] the raw scores.) It has been argued{{who|date=May 2017}} that there are nevertheless good reasons for supposing that ''g'' is [[Normal distribution|normally distributed]] in the general population, at least within a range of ±2 standard deviations from the mean. In particular, ''g'' can be thought of as a composite variable that reflects the additive effects of many independent genetic and environmental influences, and such a variable should, according to the [[central limit theorem]], follow a normal distribution.<ref>Jensen 1998, 88, 101–103</ref>