Systematic reviews bring together all existing high quality studies on a research question to provide an overview of the evidence available.
Systematic reviews systematically identify, appraise and summarise the evidence according to a predetermined protocol, they provide a reliable and unbiased assessment of a particular intervention or diagnostic test. Systematic reviews are generally regarded as the highest standard of medical evidence. They may or may not incorporate a meta-analysis, which is a statistical technique, which summarises the results of several studies.
Systematic reviews are used to communicate the results and implications of otherwise unmanageable amounts of research. In bringing together a number of separately conducted studies on the same topic, where there may be conflicting findings, and synthesising the data, a definitive conclusion may be reached. Systematic reviews are also becoming a vital part of the process of planning future research. An understanding of systematic reviews and how to implement them in practice is becoming mandatory for all professionals involved in the delivery of health care.
Meta-analytic techniques are used to combine the findings from independent studies identified in a systematic review. However, meta-analysis of published data sometimes has its limitations, and often sub-group analyses are precluded. To overcome these problems, meta-analyses that utilise individual patient data (IPD) are now initiated. IPD meta-analyses involve the collection, validation and re-analysis of ‘raw’ data from the relevant clinical trials that have looked at the research topic in question. The ‘raw’ data is usually obtained from those responsible for the original trials. Due to the nature of this kind of meta-analysis, a considerable amount of time and resources are needed as well as expertise in statistics, computing and data management.