Skip Navigation

Statistical Tests

Comparisons that have been drawn in the text of this report have been tested for statistical significance to ensure the differences are larger than those that might be expected due to sampling variation. All statements cited in the report are statistically significant at the .05 level. The statistical comparisons in this report are based on Student's t statistic. Whether the statistical test is considered significant or not is determined by calculating a t value for the difference between a pair of means or proportions and comparing this value to published tables of values, called critical values. The alpha level is an a priori statement of the probability that a difference exists in fact rather than by chance. Adjustments for multiple comparisons were not included.

The t statistic between estimates from various subgroups presented in the tables can be computed using the following formula:

equation

where x1 and x2 are the estimates to be compared (e.g., the means of sample members in two groups) and SE1 and SE2 are their corresponding standard errors.