How to Calculate Standardized Differences

When you have two groups of subjects and have measured all subjects with some numeric measure (such as height, weight, income, or number of rooms in their homes), you can express the difference between the two groups in terms of the difference between the means of each group's measurements. But interpreting this difference is dependent on a knowledge of the measurement. Another way is to compute the difference is what is known as a standardized difference. This is a dimensionless effect size measure. It also allows you to compare two differences; for instance, is the difference in heights bigger than the difference in weights?

Things You'll Need

• Spreadsheet program

Instructions

1. Enter headers for the two groups. In Excel, enter the name of group 1 in cell A1 and the name of group 2 in cell B1. For example, if you are comparing the heights of men and women, A1 could be labeled "Men" and A2 could be labeled "Women."

2. Enter the data for the two groups. Continuing the previous example, enter the heights for men in column A starting in cell A2 and the heights for women in column B starting in cell B2. Enter the heights in inches or centimeters, not feet and inches.

3. Compute the means for each group. In an empty cell in column A, click "Formulas," "Other functions," "Statistical" and then "Average." Then, in the first box, highlight the cells that have your data for men. Then do the same for column B.

4. Calculate the difference between the two means. In cell C1, enter =A5 - B5 (assuming the means are in cells A5 and B5).

5. Calculate the standard deviation of the entire sample. In cell C2, click "Formulas," "Other Functions," "Statistical" and then "Stdev." Then, in the first box, highlight all the cells in columns A and B that contain data (but not the cells that contain the averages).

6. Divide the difference by the standard deviation. In cell C3, enter =c1/c2. This is the standardized difference.

References

• A new view of statistics