infinity on the left and positive infinity on the right. Note, however, that only a very small proportion of individuals in a population will fall outside the -3? to +3? range. For example, with human heights very few people are above the +3? height level.

Percentiles represent the area under the normal curve, increasing from left to right. Each standard deviation represents a fixed percentile. Thus, rounding to two decimal places, -3? is the 0.13th percentile, -2? the 2.28th percentile, -1? the 15.87th