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Evaluation of studies of causation (aetiology)
  1. Joy Adamson, PhD
  1. Department of Health Sciences
    University of York
    York, UK

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You have been appointed as the Nurse Manager of a nursing home that provides long term care for older people and have become aware that a large proportion of residents have pressure ulcers. You know that many preventive measures, such as special beds and mattresses, are promoted, but feel unsure as to which residents are most at risk and which characteristics predict those most likely to develop pressure ulcers. Although you know there are some pressure ulcer risk prediction tools available, you are not sure that these would apply to your residents and so would like to read some original research on the topic. Your long term goal is to ensure that care is targeted at those residents at highest risk so that preventable ulcers are avoided. Your focused clinical question is which characteristics of nursing home residents place them at higher risk of pressure ulcer development?


You begin by searching Evidence-Based Nursing Online ( using the search term “pressure ulcer*”. This search identifies 8 abstracts, none of which address questions of risk factors. Similarly, a search of Evidence-Based Medicine finds no relevant studies. You try PubMed (, which is freely available online. You select the Clinical Queries search option, and the “Etiology” search because you are looking for articles concerned with the causation of pressure ulcers. You decide that your search should emphasise sensitivity over specificity so that you can minimise the risk of missing relevant articles. Your search terms are “pressure ulcer*” AND “nursing home*”. This search identifies 32 abstracts, one of which, “A longitudinal study of risk factors associated with the formation of pressure ulcers in nursing homes” sounds relevant.1


Studies that consider risk factors (often referred to as exposures) for certain diseases (often referred to as outcomes) are generally called analytical observational studies. They are …

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