Faculty of Health and Medical Sciences

Find the best evidence

Effective and efficient searching

Once you have developed a search strategy and selected your clinical resource, the next step is to implement your search. You can apply additional search tools and limits depending upon the features available in the clinical resource.

Example search string:

Patient Intervention Comparator Outcome

septic shock
severe sepsis


no steroids 


Step 1

Each clinical resource will require a different search strategy. Use the search terms (from your PICO) to identify the best subject headings or keywords.

Each clinical resource provides a range of search tools beyond Boolean operators. While you many not necessarily use all these tools (or limits) in every search that you undertake, it is useful to know that they exist as a means of improving or refining your results.

Some clinical resources, such as Medline, provide particularly sophisticated and specialised limits and filters.

Guides on using searching tools in clinical resources are available in discipline-specific resources and A-Z.

Click here to see some of the more common limits and tools in clinical resources.

Step 2

What type of question to do you have? Having the question type in mind when you start will help you determine what kind of study will best answer your question. This can then be added to your search strategy.

Type of question Best type of study/methodology Search terms and limits in Medline
Therapy Double blind randomised controlled trial Randomised controlled trial [pt]
Controlled clinical trial [pt],
Therapy [sh]
Double blind method [MeSH]
Placebo* [tw]
Treatment Outcome [MeSH]
Multicenter Study [pt]
Clinical Trial [pt]
Random* [tx]
Management [ti]
The best single-term strategy is Randomised Controlled Trial [pt])

Diagnosis Controlled trial Sensitivity and specificity [MeSH]
Diagnosis [sh]
False Negative Reactions [MeSH]
Predictive Value of Tests [MeSH]
Comparative study [MeSH]
False Positive Reactions [MeSH]
Differential Diagnosis [MeSH]
Clinical trial [pt]
The best single-term search is Sensitivity and Specificity [MeSH]

Prognosis Cohort studies, case control Prognosis [MeSH]
Cohort Studies [MeSH]
Survival Analysis [MeSH]
Morbidity [MeSH]
Outcome Assessment [MeSH]
Mortality [MeSH]
Disease profession [MeSH]
Course [ti]

Aetiology Cohort Studies Randomised controlled trial [pt]
EXP Risk [MeSH]
Causality [MeSH]
Aetiology [MeSH]
Longitudinal Studies [MeSH]
Odds [tw] AND Ratio [tw]
Comparative Study [MeSH]
Cohort Studies [MeSH]
Case-Control Studies [MeSH]
Follow-up Studies [MeSH]
Risk [tw]

Questions of Harm Randomised Controlled Trial EXP Risk [MeSH]
Toxicity [sh]
Consensus Development Conference [pt]
Consensus Development Conference, NIH [pt]
Guideline [pt]
Adverse Effects [sh]
Risk [tw]
Practice Guideline [pt]

In Medline: the information in [ ] shows which field this search term should be used in.

  • MeSH = Medical subject heading
  • sh = MeSH sub-heading
  • pt = publication type. Select this under additional limits
  • tw = text word
  • ti = title