Measurement of visual impairment in national surveys
A review of available data sources
Published: June 2012
National survey data can be used to profile groups, and to compare groups with the rest of the population. However, awareness of what datasets are available is often low. This review was conducted to identify the best available data sources for understanding the circumstances of people with sight loss in Britain.
Most British social surveys do not ask about sight loss or about types of disability and health condition
Thirteen surveys were identified and included in this review.
Five different types of survey question provide information on sight loss
- type of 'disability' or 'health condition';
- difficulty seeing and use of low vision aids (LVAs);
- specific ocular conditions;
- visual capability in different contexts;
- rating of overall vision.
Asking general questions about disability or health condition is problematic
A general question about type of 'disability' or 'health condition' is by far the most common way to obtain information on visual impairment. The format is often an initial filter question about any 'disability' or 'health condition' and a follow-up question about type.
But this approach causes problems because:
- people may not regard their sight loss as a 'disability' or 'health condition';
- often only one type of condition is coded, and sight loss is often considered as a secondary condition or an associated symptom;
- whether or not to include correctable sight loss is often not made clear in the question;
- there are issues with the coding and archiving of information on type of impairment.
Asking about specific ocular conditions gets higher reporting than general questions on types of 'disability' and 'health condition'
The English Longitudinal Survey of Aging (ELSA Wave 4 2007) asked about a range of types of ocular conditions e.g. glaucoma, diabetic eye disease or cataracts. This led to a higher level of reporting than found using general health condition approach.
Different survey questions generate very different rates of 'sight loss'
Using different questions to identify people affected by sight loss generates very different rates.
- The lowest is just 0.7% of people reporting sight loss as their primary condition (Welsh Health Survey).
- The highest is 67.1% of people reporting they have 'difficulty seeing, or wear glasses or contact lenses' (Life Opportunities Survey).
This review to identify relevant surveys was conducted using search engines and contacts. Datasets were obtained from the UK Data Archive or direct from researchers.
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