When the values of the two variables are frequently distributed in large numbers, computation, of Karl Pearson’s co-efficient of correlation involves the following three steps:
- Formation of a bivariate frequency table,
- Construction of a correlation table, and
- Application of the frequency oriented formula.
Each of the above steps is analysed as under:
(i) Formation of a bivariate frequency table.
For the construction of a bivariate table the following steps are to be taken up in turn:
- Group the values of both the variables into class intervals of suitable number and magnitude. This may be same or different for the two different variables.
- Arrange the class intervals of one of the variables in the column to the left of the table, and those of the other variable in the row at the top of the table.
- Draw up the intersection lines of rows, and columns, and thereby show the different cells against each of the class intervals in the table.
- Put the tally bars in the respective cells for each of the coordinating values, and get the total of the frequencies in the respective cells, and total of cells as well.
If the data are already in the form of a bivaribte table, it will not be necessary to form such a table any more.