What Is the First Step to Complete When Using a Systematic Review Approach
J R Soc Med. 2003 Mar; 96(3): 118–121.
Five steps to conducting a systematic review
Regina Kunz
ane German Cochrane Centre, Freiburg and Department of Nephrology, Charité, Berlin, Germany
Jos Kleijnen
2 Middle for Reviews and Dissemination, York, UK
Gerd Antes
3 German Cochrane Centre, Freiburg, Germany
Systematic reviews and meta-analyses are a fundamental chemical element of evidence-based healthcare, yet they remain in some ways mysterious. Why did the authors select sure studies and decline others? What did they do to pool results? How did a agglomeration of insignificant findings suddenly become significant? This paper, forth with a book1 that goes into more detail, demystifies these and other related intrigues.
A review earns the adjective systematic if it is based on a clearly formulated question, identifies relevant studies, appraises their quality and summarizes the show by employ of explicit methodology. It is the explicit and systematic approach that distinguishes systematic reviews from traditional reviews and commentaries. Whenever we use the term review in this paper information technology volition mean a systematic review. Reviews should never exist washed in whatever other way.
In this newspaper we provide a step-past-step caption—there are just five steps—of the methods backside reviewing, and the quality elements inherent in each step (Box one). For purposes of analogy we use a published review apropos the safety of public h2o fluoridation, simply nosotros must emphasize that our subject is review methodology, not fluoridation.
EXAMPLE: Prophylactic OF PUBLIC WATER FLUORIDATION
Yous are a public health professional in a locality that has public h2o fluoridation. For many years, your colleagues and you have believed that it improves dental health. Recently there has been pressure level from various interest groups to consider the safety of this public health intervention because they fright that it is causing cancer. Public wellness decisions have been based on professional person judgment and practical feasibility without explicit consideration of the scientific evidence. (This was yesterday; today the show is bachelor in a York reviewii , iii, identifiable on MEDLINE through the freely accessible PubMed clinical queries interface [http://www.ncbi.nlm.beak.gov/entrez/query/static/clinical.html], under 'systematic reviews'.)
Stride 1: FRAMING THE QUESTION
The research question may initially exist stated as a query in free class but reviewers prefer to pose it in a structured and explicit way. The relations betwixt various components of the question and the structure of the enquiry design are shown in Effigy 1. This paper focuses only on the question of prophylactic related to the outcomes described beneath.
Structured questions for systematic reviews and relations betwixt question components in a comparative study
Costless-class question
Is it safe to provide population-broad drinking h2o fluoridation to prevent caries?
Structured question
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The populations—Populations receiving drinking water sourced through a public water supply
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The interventions or exposures—Fluoridation of drinking h2o (natural or bogus) compared with not-fluoridated water
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The outcomes—Cancer is the main consequence of involvement for the fence in your health authority
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The study designs—Comparative studies of any design examining the harmful outcomes in at least 2 population groups, one with fluoridated drinking water and the other without. Harmful outcomes can be rare and they may develop over a long time. At that place are considerable difficulties in designing and conducting safety studies to capture these outcomes, since a large number of people need to be observed over a long menstruum. These circumstances demand observational, not randomized studies. With this background, systematic reviews on safety have to include testify from studies with a range of designs.
Footstep two: IDENTIFYING RELEVANT PUBLICATIONS
To capture equally many relevant citations every bit possible, a wide range of medical, environmental and scientific databases were searched to identify primary studies of the effects of h2o fluoridation. The electronic searches were supplemented past hand searching of Index Medicus and Excerpta Medica back to 1945. Furthermore, various cyberspace engines were searched for spider web pages that might provide references. This try resulted in 3246 citations from which relevant studies were selected for the review. Their potential relevance was examined, and 2511 citations were excluded as irrelevant. The full papers of the remaining 735 citations were assessed to select those primary studies in man that directly related to fluoride in drinking water supplies, comparison at to the lowest degree two groups. These criteria excluded 481 studies and left 254 in the review. They came from xxx countries, published in 14 languages betwixt 1939 and 2000. Of these studies 175 were relevant to the question of rubber, of which 26 used cancer equally an effect.
Footstep three: ASSESSING STUDY QUALITY
Design threshold for study choice
Adequate written report design as a mark of quality, is listed as an inclusion criterion in Box 1. This approach is virtually applicable when the main source of evidence is randomized studies. However, randomized studies are most impossible to conduct at community level for a public health intervention such every bit water fluoridation. Thus, systematic reviews assessing the condom of such interventions have to include evidence from a broader range of report designs. Consideration of the type and amount of research likely to be available led to inclusion of comparative studies of any design. In this way, selected studies provided information virtually the harmful effects of exposure to fluoridated water compared with non-exposure.
Quality assessment of safety studies
After studies of an adequate design have been selected, their in-depth assessment for the risk of diverse biases allows us to gauge the quality of the evidence in a more refined fashion. Biases either exaggerate or underestimate the 'truthful' outcome of an exposure. The objective of the included studies was to compare groups exposed to fluoridated drinking water and those without such exposure for rates of undesirable outcomes, without bias. Safety studies should ascertain exposures and outcomes in such a style that the risk of misclassification is minimized. The exposure is probable to be more accurately ascertained if the written report was prospective rather than retrospective and if it was started soon subsequently water fluoridation rather than later. The outcomes of those developing cancer (and remaining free of cancer) are likely to be more than accurately ascertained if the follow-up was long and if the cess was bullheaded to exposure status.
When examining how the effect of exposure on upshot was established, reviewers assessed whether the comparison groups were similar in all respects other than their exposure to fluoridated h2o. This is considering the other differences may exist related to the outcomes of interest independent of the drinking-water fluoridation, and this would bias the comparison. For instance, if the people exposed to fluoridated h2o had other take chances factors that made them more than decumbent to take cancer, the apparent association betwixt exposure and outcome might be explained past the more frequent occurrence of these factors amidst the exposed grouping. The technical word for such defects is misreckoning. In a randomized study, confounding factors are expected to be roughly every bit distributed betwixt groups. In observational studies their distribution may be diff. Primary researchers can statistically adjust for these differences, when estimating the effect of exposure on outcomes, by utilize of multivariable modelling.
Put but, apply of a prospective design, robust ascertainment of exposure and outcomes, and control for confounding are the generic issues one would look for in quality assessment of studies on prophylactic. Consequently, studies may range from satisfactorily meeting quality criteria, to having some deficiencies, to not coming together the criteria at all, and they can be assigned to i of three prespecified quality categories every bit shown in Tabular array i. A quality hierarchy can then be developed, based on the caste to which studies comply with the criteria. None of the studies on cancer were in the high-quality category, but this was because randomized studies were not-existent and command for confounding was not always ideal in the observational studies. There were eight studies of moderate quality and 18 of low quality.
Table 1
Description of quality cess of studies on prophylactic of public water fluoridation
| Quality categories | High | Moderate | Low |
|---|---|---|---|
| Prospective design | Prospective | Prospective | Prospective or retrospective |
| Ascertainment of exposure | Study began within 1 year of fluoridation | Study began within 3 years of fluoridation | Study began >3 years after fluoridation |
| Observation of outcome | Follow-up for at least five years and blind assessment | Long follow-up and blind assessment | Curt follow-up and unblinded assessment |
| Control for confounding | Adjustment for at least three confounding factors (or utilise of randomization) | Adjustment for at least one confounding factor | No aligning for confounding factors |
STEP 4: SUMMARIZING THE Testify
To summarize the evidence from studies of variable design and quality is not piece of cake. The original review3 provides details of how the differences between study results were investigated and how they were summarized (with or without meta-analysis). This paper restricts itself to summarizing the findings narratively. The clan between exposure to fluoridated h2o and cancer in general was examined in 26 studies. Of these, 10 examined all-cause cancer incidence or mortality, in 22 analyses. Of these, 11 analyses found a negative association (fewer cancers due to exposure), 9 constitute a positive one and 2 found no association. Only 2 studies reported statistically significant differences. Thus no clear association between water fluoridation and increased cancer incidence or mortality was apparent. Bone/joint and thyroid cancers were of detail concern because of fluoride uptake by these organs. Neither the six studies of osteosarcoma nor the 2 studies of thyroid cancer and h2o fluoridation revealed significant differences. Overall no association was detected between water fluoridation and bloodshed from any cancer. These findings were also borne out in the moderate-quality subgroup of studies.
Pace 5: INTERPRETING THE FINDINGS
In the fluoridation example, the focus was on the safety of a community-based public wellness intervention. The generally low quality of available studies means that the results must be interpreted with caution. However, the elaborate efforts in searching an unusually large number of databases provide some safeguard against missing relevant studies. Thus the evidence summarized in this review is probable to be as good as information technology will make it the foreseeable futurity. Cancer was the harmful effect of most interest in this example. No clan was found between exposure to fluoridated water and specific cancers or all cancers. The estimation of the results may be generally limited considering of the depression quality of studies, merely the findings for the cancer outcomes are supported by the moderate-quality studies.
RESOLUTION
After having spent some time reading and understanding the review, you are impressed by the sheer corporeality of published work relevant to the question of condom. Withal, you are somewhat disappointed by the poor quality of the primary studies. Of course, examination of safety only makes sense in a context where the intervention has some benign event. Benefit and harm accept to be compared to provide the ground for decision making. On the upshot of the beneficial result of public h2o fluoridation, the review3 reassures you that the health authority was right in judging that fluoridation of drinking h2o prevents caries. From the review you too discovered that dental fluorosis (mottled teeth) was related to concentration of fluoride. When the interest groups enhance the result of safety over again, you will exist able to declare that in that location is no evidence to link cancer with drinking-water fluoridation; nevertheless, you will take to come up clean about the risk of dental fluorosis, which appears to be dose dependent, and you may want to measure the fluoride concentration in the water supply and share this information with the interest groups.
The power to quantify the condom concerns of your population through a review, albeit from studies of moderate to low quality, allows your health dominance, the politicians and the public to consider the balance between beneficial and harmful effects of h2o fluoridation. Those who see the prevention of caries as of primary importance volition favour fluoridation. Others, worried about the disfigurement of mottled teeth, may prefer other means of fluoride administration or even occasional treatment for dental caries. Whatsoever the opinions on this matter, you lot are able to reassure all parties that there is no evidence that fluoridation of drinking h2o increases the gamble of cancer.
CONCLUSION
With increasing focus on generating guidance and recommendations for practice through systematic reviews, healthcare professionals demand to understand the principles of preparing such reviews. Here nosotros have provided a brief stride-by-step caption of the principles. Our bookone describes them in detail.
References
Articles from Journal of the Royal Society of Medicine are provided here courtesy of Regal Society of Medicine Press
Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC539417/
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