a simple nonparametric procedure used to determine whether a sample has the same median value as another sample or a reference population. Consider a farmer who wants to know whether he or she can grow a particular crop that requires soil with a median acidity level (pH) of 8. The farmer measures the soil in several different areas on his or her property and then compares the pH value of each measurement to the required median value. Each acidity reading above 8 is marked positive using a + sign and each reading is marked negative with a – sign. If the proportion of positive signs for the group of measurements is significantly different from the proportion of negative signs, then the farmer's sample soil data have a different median than the one required and the desired crop cannot be planted. Unlike the Wilcoxon signed-ranks test, the sign test does not take into account the magnitude of the observed differences from the median.