© 2008 The Royal College of Psychiatrists
Correspondence |
Limitations of observational studies with known confounders
*Fromeside, Blackberry Hill, Bristol BS16 1ED, email: ngalappathie{at}doctors.org.uk
Fromeside
The recent article by Dibben et al (2008) provides positive evidence that crisis resolution and home treatment teams for older people reduce admission rates to hospital by 31%. Their findings are based upon a 6-month observational study conducted before and after the introduction of the new service. We believe the results are unreliable and should be treated with caution.
The analysis of baseline characteristics shows no significant difference between the patient groups; however, it is misleading as external factors are likely to confound the results in this case.
The authors confirm that during the study period a dementia care ward was closed, as were two day-hospitals. These changes are likely to represent known confounding variables. Closure of the dementia ward will invariably lead to reduced admission rates as a direct result of reduced capacity to admit service users. The day hospital closure may also serve to raise the clinical threshold required for admission given the reduction in day attendance capacity.
No data is provided regarding in-patient bed capacity and how this was reduced following bed closures, thus readers are unable to estimate the magnitude of the potential impact upon results. In addition, no data is provided for the potential known confounding variable of out-of-area admissions, which can occur when a hospital reaches full occupancy.
Clearly, the gold standard for study design would have been a randomised controlled trial. This is often not possible given feasibility implications. Ideally, the authors should have used a control group of service users who were not treated by the new service. This should then have been followed by appropriate use of multivariate regression analysis to account for the effects of the known confounding variables. The authors rely on past randomised research to support their findings (Johnson et al, 2005; Joy et al, 2006). The participants of the cited studies were not solely older adults and the results are therefore not directly generalisable to their sample. We accept their research is novel and designed with service limitations in mind, but we believe they offer only a basic understanding of their subject.
References
- DIBBEN, C., SAEED, H., STAGIAS, K., et al
(2008) Crisis resolution and home treatment teams for older
people with mental illness. Psychiatric Bulletin,
32, 268
-270.
[Abstract/Free Full Text] - JOHNSON, S., NOLAN, F., PILLING, S., et al
(2005) Randomised controlled trial of acute mental health care by
a crisis resolution team: the north Islington crisis study.
BMJ, 331, 599
.
[Abstract/Free Full Text] - JOY, C. B., ADAMS, C. E. & RICE, K. (2006) Crisis intervention for people with severe mental illnesses. Cochrane Database of Systematic Reviews, 18, CD001087 .
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