Distribution of Intelligence

Current criticisms of use of normal curve in assessing intelligence seem to arise from misconceptions both about nature of evidence available and about hypothesis assumed. theoretical evidence suggests that individual differences in intelligence are effect partly of multifactorial and partly of unifactorial inheritance: on this basis distribution to be expected would be bell‐shaped, but more or less skewed, i.e. a ‘type IV’ rather than a ‘normal’ curve. empirical evidence is mainly derived from tests scaled independently of resulting distribution. With such methods, provided samples are sufficiently large and complete, frequency‐curves obtained exhibit small but significant deviations from strict normality. If, however, specific cases of mental deficiency are omitted, then, for most practical purposes, resulting distributions can be treated as approximately normal.