Example of Mood’s Median Test

An environmental scientist wants to determine whether temperature changes in the ocean near a nuclear power plant affect the growth of fish. The scientist randomly divides 25 newly hatched fish into four groups and places each group into a separate, simulated ocean environment. The simulated environments are identical except for temperature. Six months later, the scientist measures the weights of the fish. To determine whether the median weight of the fish differs among the four groups, the scientist uses Mood's median test.

  1. Open the sample data, FishWeights.MTW.
  2. Choose Stat > Nonparametrics > Mood’s Median Test.
  3. In Response, enter Weight.
  4. In Factor, enter Temp.
  5. Click OK.

Interpret the results

For each factor level, Minitab displays the median, interquartile range, and a confidence interval for the population median. You can be 95% confident that the population median for each group is within the corresponding interval.

Because the p-value of 0.697 is greater than the commonly used significance level of 0.05, the scientist fails to reject the null hypothesis. The differences between the median weights are not statistically significant.

Mood's Median Test: Weight versus Temp

Descriptive Statistics Temp Median N <= Overall Median N > Overall Median Q3 – Q1 95% Median CI 38 19 4 3 4.00 (17.4667, 22.5333) 42 19 3 3 9.50 (15.3571, 25.6429) 46 22 2 4 7.25 (15.7857, 26.5714) 50 18 4 2 4.25 (14.4286, 20.6429) Overall 19
Test Null hypothesis H₀: The population medians are all equal Alternative hypothesis H₁: The population medians are not all equal

DF Chi-Square P-Value 3 1.44 0.697

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