Many statistical tests require the data to follow the normal distribution. Sometimes it is difficult to ascertain whether or not the data follow the normal distribution. In such cases it is necessary to use a statistical test that does not require the data to follow a particular distribution. Such a test is called a non-parametric or distribution free test. This test is an example of one of these. This test is a non parametric test, based on the direction of the plus and minus sign of the observations.  It is also called the binominal sign test.

Sign test is an alternative to sample‘t-test’ for:

  1. One-sample t-test to test the null hypothesis that the mean of a distribution is equal to some specified value, (One- Sample)
  1. Paired t-test for testing the equality of difference of two population means for paired sample, (Two- Sample) when the data do not follow a normal distribution.

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