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Systematic Reviews

Specialised advice for planning, researching and writing Systematic Reviews.

What are inclusion and exclusion criteria

Inclusion and exclusion criteria are used to define those articles of interest.

These criteria are usually applied to the results of a search and are not used to limit the search results.

Many of the criteria are determined by the elements of the question, such as limiting selected papers by the population, participants or problem under investigation, the type of intervention and outcomes.

The type of question being asked may also determine the inclusion or exclusion criteria for types of studies which may be used in the review.

Examples:

Does the use of chlorhexidine mouthwash reduce gingivitis?

Included:

  • randomised controlled trials (RCTs)
  • duration of mouthrinsing was at least 4 weeks
  • children or adults with gingivitis or periodontitis capable of performing normal mechanical oral hygiene procedures
  • chlorhexidine mouthrinse (used at any concentration, volume, frequency or duration of rinsing) used in conjunction with mechanical oral hygiene procedures

Excluded:

  • studies where the duration of mouthrinsing was less than 4 weeks
  • cross-over studies in case chlorhexidine could exert an effect beyond the washout period
  • where chlorhexidine mouthrinse was used as a monotherapy in the absence of mechanical oral hygiene procedures
  • where the chlorhexidine mouthrinse formed part of a combined intervention with other agents that the comparator arm(s) did not receive
  • where the mechanical oral hygiene procedures were not the same in both the chlorhexidine mouthrinse and the comparator arm(s)
  • where chlorhexidine mouthrinse was applied locally e.g. with a brush or via subgingival irrigation
  • where gingivitis was not measured using a recognised index/scale.

Limiting the search

Depending on the scope and size of the review, limits to the search may or may not apply.

Some common limiters often applied to searches do not always apply as using limits at the search stage may omit relevant results from the review. However, in other cases they may be used.

Two of the most common limiters that may be applied at the search stage of a systematic review are date and language.

Date range:

Topics should not be limited by date if there is no clear date that applies.

However some topics will be limited by date by the nature of the question being asked.

Examples of this may be:

  • When a particular treatment started being used.
  • When a policy or regulation became adopted.
  • When an older systematic review is being updated to include new information.

Language:

In thorough systematic reviews, results should not be limited by language and results in other languages should be translated if possible.

However this is not always possible, especially for reviews being undertaken by individuals.

If results are limited by language, this should be noted as a limitation of the review.

Types of studies

The following table shows some different types of questions that may be asked as part of systematic reviews, and the types of studies that may apply. Depending on the question being asked, these may help determine the types of studies that may be used as part of the inclusion or exclusion criteria.

Type of question
Description
Types of studies
Treatment or Therapy or Solution
Effect of intervention on patient, population or setting of interest Trial or experiment; Cohort; Case control; Case series
Harm or Aetiology (Causation)

Effect of potentially harmful agents

Cross sectional or prospective, blind comparison to gold standard
Diagnosis

Power of a test to differentiate between those with or without a disease or condition

Trial or experiment; Cohort; Case control; Case series
Prognosis or Forecast

Estimate of a likely course over time

Cohort; Case control; Case series
Social Sciences

Prevention
Reducing chance by changing risk factors or diagnosing and treating early Trial or experiment; Cohort; Case control; Case series
Meaning
Participants experience or attitudes Narrative; Ethnographic; Phenomenological; Grounded theory; Case studies

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