Health and Safety
Executive / Commission
Statistics
The LFS collects data on a sample of the population. To convert this information to give estimates for the population, the sample data is weighted. Each case is given a weight which can be thought of as the number of people that case represents. This weighting factor takes account of differential non-response among different sub-groups in the population. This weighting procedure involves grossing data to sub-regional population estimates and then adjusting for the estimated age and sex composition, by region.
For more detailed information about the procedures used, see LFS User Guide Volume 1: Background and Methodology
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These weighting factors are provided to HSE by the Office for National Statistics (ONS) along with the LFS dataset itself.
Whilst the ONS provided weighting factors take account of non-response to the LFS itself, they do not account for non-response to individual questions within it, in particular the Workplace Injury and SWI survey modules’ screening questions. In 2006/07, 7.8% of eligible respondents did not respond to either or both of the screening questions within the workplace injury and SWI survey modules (most of whom were unavailable for interview). Since this non-response is not accounted for in the standard LFS weighting procedure, an adjustment is made to the weights to take account of this non-response and provide more reliable estimates.
For the non-response adjustments a procedure is implemented (using the software ‘SPSS AnswerTree’) to identify demographic and employment-related variables and codes that best describe the pattern of response to the ill health and workplace injury screening questions. The procedure progressively splits the sample into groups between which the response rates differ to a statistically significant extent. The adjustment for non-response then involves multiplying the standard LFS weights by the reciprocal of the response rate within each of the groups identified.