## Information

**C** - continuity correction, when U > μ: C = -0.5, when U < μ: C = 0.5

### Target

Unlike t-test that compares the means, the Mann-Whitney U test compares a randomly selected value from group1 to a randomly selected value from group2.

When the two distributions have a similar

**shape** you can use the test to compare also the

**medians**.

When the two distributions have a similar

**symmetrical shape**, you can use the test to compare also the

**means**.

more### Method

**Automatic** - when n

_{1}≤20 and n

_{2}≤20 and the data doesn't have ties, the tool uses the exact value, otherwise the tool uses the z approximation.

**Exact** - when n

_{1}≤20 and n

_{2}≤20 the tool uses the exact value, calculated base on all the possible combinations, otherwise the tool uses the z approximation.

**Z approximation** - the tool uses the z approximations.

**Continuity correction** - relevant only for the Z approximation. It is used since a continuous distribution is used to calculate a discrete distribution.

## R Code

The following R code should produce similar results: