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From Table 3.3, the proportion of subjects with a positive outcome under the test treatment is and under the control treatment is .

The difference in proportions is given by

In prospective studies the proportion is also known as the risk and the difference in proportions as the risk difference (RD)

When one ignores the sign, the above quantity is also known as the absolute risk difference (ARD), that is.

where the symbols || mean to take the absolute value.

If we anticipate that the treatment to reduce some bad outcome (such as deaths) then it may be known as the absolute risk reduction (ARR). If we anticipate that the exposure/treatment will increase some bad outcome (such as deaths) then it may be known as the absolute risk excess (ARE).