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How to measure time lost to sickness absence

There are four main ways of measuring time lost to sickness absence in the workplace. These are:

Lost time rate

The most commonly used measure is the lost time rate which shows the percentage of total time available that has been lost due to any type of absence during a certain time period. To calculate the lost time rate, divide the total absence in hours or days in the chosen period by the possible total in hours or days in that period, then multiply by 100.

For instance, take a total absence of 120 hours in a possible 1500 total hours available in that period, the lost time rate is: 120/1500 x 100 = 8% (rounded to the nearest 0.5%)

The lost time rate is useful as a general measure of the gravity of sickness absence levels for an organisation. Teams or departments who want to ascertain whether or not there are absence issues in certain areas can also use this measure. But, as this measure gives only an overview of the time lost, a small number of employees who are on long-term sickness absence or a larger number of employees who have a high number of short-term sickness absences can distort the figures. To see the extent of the problem, a better measure to use would be the frequency rate.

Frequency rate

The frequency rate calculates the average number of periods of absence per employee as a percentage. It gives no indication of the length of each sickness absence period and no indication of employees who have taken more than one period of absence. It is calculated by dividing the number of spells of absence in the period by the number of employees in the period, and then multiplying by 100.

So if you employed an average of 75 staff members in a three-month period, and had a total of 19 periods of sickness absence in that time, the frequency rate for absence would be: 19/75 x 100 = 25.5% (rounded to the nearest 0.5%)

Individual frequency rate

To show as a percentage the number of individual employees who have been absent during a period of time, you will need to use the individual frequency rate. Like the frequency rate, it doesn’t show the length of each sickness absence period. To calculate the individual frequency rate, divide the number of employees taking one or more spells of absence during a period by the number of employees in the period, then multiply by 100.

To illustrate this measure using the frequency rate example above, if the 19 periods of absence in a three-month period consisted of the absence of 11 employees, one who was absent four times, one who was absent three times, two who were absent twice and 7 who were absent once, the individual frequency rate would be: 11/75 x 100 = 14.5% (rounded to the nearest 0.5%)

Bradford factor

To identify the organisational disturbance caused by persistent short-term absence for individual employees, the Bradford factor should be employed. This method gives extra weight to the number of periods of sickness absence taken per employee. The Bradford score is S x S x D – S being the number of spells of absence in 52 weeks taken by an employee and D the number of days of absence in 52 weeks taken by that employee.

A working example would be, if an employee has four spells of absence that total nine days of absence in 52 weeks, the Bradford factor would be: 4 x 4 x 9 = 144

For organisations setting absence triggers to investigate absence when it reaches a certain trigger level, the Bradford factor can be a useful measure of sickness absence.

For more information on setting absence triggers to help manage sickness absence in your organisation, you may find the following article useful:

How to use action and metric figures to manage absence