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systematic review

Is there an evidence base for children in primary care?

Peter Gill
Last edited 9th August 2011

A recent article in PlosONE of Cochrane reviews relevant to children in primary care states there is a mismatch between the focus of published research and the clinical activity for children in general practice. Not only in the UK but in a number of countries: Australia, Netherlands, US and the UK.

What’s odd is that in a condition such as asthma despite representing 3-5% of consultations, it is the focus of nearly one-quarter of all reviews. On the other hand, despite the increasing burden of skin conditions which lead to one-quarter of all visits only 7% of reviews were relevant.

Non-drug interventions (such as counseling) are an important part of general practice yet they are virtually non-existent in evidence syntheses and research funding. Over half of the reviews studied drug interventions in children while 69% of all controlled trials in children assess drug products.

Whilst the number of systematic reviews published is skyrocketing (over 2,500 in 2007 alone) there continues to be avoidable waste in the production and reporting of research evidence (read more on cebmblog’s recent post). Yet, there has not been a similar increase in children reviews in primary care. Since 2000, the percentage of reviews on children nearly tripled compared to a much smaller increase in primary care reviews.

Why the mismatch? Likely due to multiple factors: absence of primary trials, lack of author interests, public funding poorly correlates with disease burden, more interventions in certain conditions (such as asthma) than others, lack of additional academic training in child health and lack of an overall map of the evidence.

Despite the reasons the mismatch is clear and needs to be addressed. Further work needs to be done to look at how the reviews inform clinical practice. Improving the evidence base for children in primary care is a no-brainer. So how and who should sort this out? Initial steps should include encouraging Cochrane Review Groups, funders, and other relevant organizations to prioritize topics.

The recently created PROSPERO international register of systematic reviews is a step forward to help minimize waste.

Is there an evidence base for children in primary care? Not yet.

There are several historical lessons showing why the results of studies and trials should always be viewed in the broader context of all the knowledge in that area. The most commonly used cautionary tale is that of babies lying on their side and risk of sudden infant death. The unfortunately named Dr Benjamin Spock first published his famous book, “Baby and Child Care”, in 1946. In it, he advocated lying babies on their side and sold 19 million copies. Trials as early as the mid-1980s clearly showed that there were more deaths in babies lying on their side compared with babies lying on their backs. However, scientists continued to conduct over 20 more trials which all showed the same result. If these scientists had conducted a proper systematic review and combined the results of previous analyses (meta-analysis), they would have found that further trials were totally unnecessary because the data already showed that laying a baby on its side was harmful. Instead, their trials actually led to tens of thousands of infant deaths which may have been avoided if practice had changed before 2003. Setting the results of new studies in the context of a systematic review of the results of all other relevant studies would become straightforward if systematic reviews were always done before embarking on new research. In new areas of research, such reviews should be performed as data is accumulated in order to look at overall “pooled” trends.

James Lind, a Scottish physician, is credited with performing the first systematic review in 1753, titled “Treatise of the Scurvy”. In this work, he noted,

“As it is no easy matter to root out prejudices, …. it became requisite to exhibit a full and impartial view of what had hitherto been published on the scurvy, and that in a chronological order, by which the sources of these mistakes may be detected. Indeed, before the subject could be set in a clear and proper light, it was necessary to remove a great deal of rubbish.”

His observations have stood the test of time. A systematic review must involve 4 steps: (1) a clearly formulated question; (2) finding relevant studies; (3) appraisal of quality of the studies; and (4) summary of the evidence by use. The first step is crucial, not just in systematic reviews, but in any area of evidence-based medicine. Four aspects of any study question must be clearly defined in order to make any results meaningful: (1) the population being studied; (2) the intervention or exposure being studied; (3) the comparison group used in the study; (4) the outcome that was measured in the study.

Meta-analysis just means that we are combining the numbers from individual studies or trials to give the overall effect from all available data. A meta-analysis of data can only be done if the included studies are comparable and this process will give weighting to studies with larger numbers of patients and more precise data. For an example, see my previous blog regarding aspirin in primary prevention.

The BBC this week reported that patients do not need to fast before having their cholesterol tested , and that this could save greatly on the cost and convenience of testing for cholesterol in patients. This conclusion was only possible because of a systematic review done by Cambridge researchers, published in the Journal of the American Medical Association. They looked at the available evidence for measuring cholesterol and lipids in the blood and cardiovascular risk, which involved going through the individual records of over 300 000 patients involved in 68 long-term studies. Nobody said that doing systematic reviews was always easy but if we don’t do them, we will miss the big picture.

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