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Cochran

Cochran test is a non-parametric test for a difference in proportion in two or more paired dichotomous samples.

The requirements of the test are:

  • At least two dichotomous paired samples measured on a nominal or ordinal scale.
  • Observations must be classified using the same two groups.


Arranging the dataset

Data in existing Excel worksheets can be used and should be arranged in a List dataset layout. The dataset must contain at least two nominal or ordinal scale variables dichotomised by the same groups and criteria.

When entering new data we recommend using New Dataset to create a new k variables (categorical) dataset ready for data entry.

Using the test

To start the test:

  1. Excel 2007:
    Select any cell in the range containing the dataset to analyse, then click Compare Pairs on the Analyse-it tab, then click Cochran.
  2. Excel 97, 2000, 2002 & 2003:
    Select any cell in the range containing the dataset to analyse, then click Analyse on the Analyse-it toolbar, click Compare Pairs then click Cochran.

  3. Tick Variables to compare.
  4. Click OK to run the test.

The report shows the number of observations analysed, and, if applicable, how many missing values were excluded. The number of observations of each group in each sample are summarised in a contingency table.

The Cochran statistic and hypothesis test are shown. The p-value is the probability of rejecting the null hypothesis, that the samples have the same proportions in each group, when it is in fact true. A significant p-value implies that at least two samples have different proportions in each group. 

METHOD The p-value is calculated using the chi-square approximation (see [2]).

Further reading & references

  1. Handbook of Parametric and Nonparametric Statistical Procedures (3rd edition)
    David J. Sheskin, ISBN 1-58488-440-1 2003; 867.
  2. Practical Non-parametric Statistics (3rd edition)
    Conover W.J. ISBN 0-471-16068-7 1999; 251.


(click to enlarge)