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Nutrition: Effective Library Research: 6. Clinical evidence

Online tutorial introducing you to the skills and techniques needed for effective library research.

As part of your research you may need to consider clinical evidence and practice implications. The following provides an introduction to locating clinical evidence. It's important to consider the type of evidence you need as this will influence where you search.

Medical research can generally be divided into two categories:

Primary research: Original research carried out in a clinical or laboratory setting. Examples include: observational studies and randomized controlled trials.

Secondary research: Analysis of primary research, often to pool data or review the body of evidence on specific conditions. Examples include: systematic reviews and guidelines.

The evidence pyramid illustrates different evidence types according to their methodological strength. Each level of the pyramid represents a different type of study. As we go up the pyramid, the stronger (i.e. more reliable and higher quality) the evidence. We should aim to locate evidence higher in the pyramid whenever available. 

Hierarchy of evidence

Hierarchies of evidence help you to identify the most robust evidence to answer your research question by helping you decide what evidence to look for. Generally study designs towards the top of the hierarchy have measures in place to minimise bias, so they are good places to start.

Different research questions require different study designs, so there is no one hierarchy of evidence. The pyramid below details a hierarchy of evidence for effectiveness questions, i.e. are steroid tablets more effective than combination inhalers in treating adults with severe asthma?

There won't always be high level evidence such as systematic reviews or randomised controlled trials available in the area you wish to research, so you will need to consider evidence further down the pyramid.

Resources for finding clinical evidence

NICE Evidence is a search engine which allows you to search for guidelines, health technology assessments and economic evaluations. You can access prescribing information through the BNF and BNFC and up-to-date Clinical Knowledge Summaries (CKS) that condense the evidence-base on particular topics. 

TRIP database is a clinical search engine, that has been designed to help you find evidence-based content quickly. TRIP will help you identify research evidence, as well as images, videos and patient information leaflets. 

The Cochrane Library is home to two databases. The Cochrane Database of Systematic Reviews will help you identify systematic reviews and protocols (a comprehensive description of a plan for a systematic review, including the rationale, hypothesis and the methods the authors intend to follow.) 

Cochrane Central Register of Controlled Trials (CENTRAL), can help you identify randomized and quasi-randomized controlled trials. It's worth noting that you won't be able to access the full text of the studies. You'll need to try and track down the full-text of the study using a research database such as MEDLINE or EMBASE.

Medline contains over 25 million citations in lifesciences and biomedicine. Coverage is from 1946 - present. You may already be familiar with searching Medline through PubMed. The articles indexed are the same, although PubMed coverage starts from 1966. 

This tutorial focuses on searching Medline via the Ovid platform. This platform is good for running advanced searches and provides access to full-text articles where available through university subscriptions.

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