Most descriptive comparisons in NCES reports are tested using Student's t statistic. Statistical significance is determined by calculating t values for differences between pairs of means or proportions and comparing these with published values of t for two-tailed hypothesis testing, using a 5 percent probability of a Type I error (a significance level of .05).

Student's t values may be computed to test the difference between estimates with the Independent Estimate t-Test Tool below. Note that this formula is valid only for independent estimates (e.g., it is not appropriate for comparing a total percentage with that for a subgroup that is included in the total).