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Public Health 190 (Bradman)

Does the Dose Make the Poison? Introduction to Toxicology and Risk Assessment

Research Question Frameworks

  • Population (who are you screening? may include animal studies.)
  • Exposure (benefits and harms, identification of exposures as risk factors or within risk assessments)
  • Comparator/ Comparison (are you comparing to? cut-off point?)
  • Outcome (what are the outcomes? Is there a specific one you are looking at?)

Table 1. Five paradigmatic approaches and examples for identifying the exposure and comparator in systematic review and decision-making questions.

Potential systematic-review or research context


PECO example

1. Calculate the health effect from an exposure; describing the dose-effect relationship between an exposure and an outcome for risk characterization.

Explore the shape and distribution of the relationship between the exposure and the outcome in the systematic review.

Among newborns, what is the incremental effect of 10 dB increase during gestation on postnatal hearing impairment?

2. Evaluate the effect of an exposure cut-offa on health outcomes, when the cut-off can be informed iteratively by the results of the systematic review.

Use cut-offs defined based on distribution in the studies identified in the systematic review.

Among newborns, what is the effect of the highest dB exposure compared to the lowest dB exposure (e.g. identified tertiles, quartiles, or quintiles) during pregnancy on postnatal hearing impairment?

3. Evaluate the association between an exposure cut-off and a comparison cut-off, when the cut-offs can be identified or are known from other populations.

Use mean cut-offs from external or other populations (may come from other research).

Among commercial pilots, what is the effect of noise corresponding to occupational exposure compared to noise exposure experienced in other occupations on hearing impairment?

4. Identify an exposure cut-off that ameliorates the effects on health outcomes.

Use existing exposure cut-offs associated with known health outcomes of interest.

Among industrial workers, what is the effect of exposure to <80 dB compared to ≥80 dB on hearing impairment?

5. Evaluate the potential effect of a cut-off that can be achieved through an intervention to ameliorate the effects of exposure on health outcomes.

Select the comparator based on what exposure cut-offs can be achieved through an intervention.

Among the general population, what is the effect of an intervention that reduces noise levels by 20 dB compared to no intervention on hearing impairment?

  • dB: decibel; PECO: population, exposure, comparator, outcome(s).
  • a. Cut-off is a broad term referring to thresholds, levels, durations, means, medians, or ranges of exposure.

Morgan, R. L., Whaley, P., Thayer, K. A., & Schünemann, H. J. (2018). Identifying the PECO: a framework for formulating good questions to explore the association of environmental and other exposures with health outcomesEnvironment international121(Pt 1), 1027.

As you consider the scope of your research, think about these concepts:

  • Population / Problem (who are you screening? Why?)
  • Intervention (what are you evaluating? e.g., a treatment, an intervention, etc)
  • Comparison (are you comparing this group to another group, e.g. a placebo group?)
  • Outcome (what are the outcomes? Is there a specific one you are looking at?)
  • Timeframe (is there a set timeframe you are working with?)
  • Setting (primary care? Outpatient? etc.)

(From Lackey, M. (2013). Systematic reviews: Searching the literature [PowerPoint slides]. Retrieved from

How can screening for depression and feedback of results to providers versus no screening and feedback improve outcomes of major depression in primary care settings for adult populations?

  • Population / Problem: adults / depression (major)
  • Intervention: screening, feedback
  • Comparison: none
  • Outcome: no particular outcomes specified
  • Timeframe: none
  • Setting: primary care

(From Lackey, M. (2013). Systematic reviews: Searching the literature [PowerPoint slides]. Retrieved from

Search Terms

You can use your PECO or PICOTS concepts as preliminary search terms. The important terms in this question:

In adults, is screening for depression and feedback of results to providers more effective than no screening and feedback in improving outcomes of major depression in primary care settings?

...might include:





Major depression

Primary Care

(From Lackey, M. (2013). Systematic reviews: Searching the literature [PowerPoint slides]. 

It can also be helpful to use controlled vocabulary with, and in addition to, keywords. Controlled vocabulary systems, such as the Medical Subject Headings (MeSH) or Library of Congress Subject Headings (LCSH), use pre-set terms that are used to tag resources on similar subjects. See boxes below for more information on finding and using subject terms.

Not all databases will have subject heading searching and for those that do, the subject heading categories may differ between databases. This is because databases classify articles using different criteria.

Using the keywords from our example, here are some MeSH terms for:

Adults: Adult (A person having attained full growth or maturity. Adults are of 19 through 44 years of age. For a person between 19 and 24 years of age, YOUNG ADULT is available.)

Screening: Mass Screening (Organized periodic procedures performed on large groups of people for the purpose of detecting disease.)

Major depression: Depressive Disorder, Major (Marked depression appearing in the involution period and characterized by hallucinations, delusions, paranoia, and agitation.)

Here is a LCSH subject term for:

Depression: Depression, mental (Dejection ; Depression, Unipolar ; Depressive disorder ; Depressive psychoses ; Melancholia ; Mental depression ; Unipolar depression)

keywords vs subjects chart

  • Most EBSCO databases have a tool to help you discover subject terms. See Academic Search Complete > Subject Terms and Academic Search Complete > Subject Terms: Thesaurus
  • Most ProQuest databases have a tool to help you discover subject terms: See PsycInfo > Thesaurus
  • When you find a useful article, look at the article's Subject Headings (or Subject or Subject Terms), and record them as possible terms to use in a subject term search.

Here is an example of the subject terms listed for a systematic review found in PsycINFO, "Primary care screening for and treatment of depression in pregnant and postpartum women: Evidence report and systematic review for the US Preventive Services Task Force" (2016).

MeSH are standardized terms that describe the main concepts of PubMed/MedLine articles. Searching with MeSH can increase the precision of your search by providing a consistent way to retrieve articles that may use different terminology or spelling variations. 

Note: new articles will not have MeSH terms; the indexing process may take up to a few weeks for newly ingested articles. 

Use the MeSH database to locate and build a search using MeSH.

  Access the Mesh Database from the PubMed homepage under the Explore menu.

To search the MeSH database:

  • Search for 1 concept at a time.
  • If you do not see a relevant MeSH in the results, search again with a synonym or related term.
  • Click on the MeSH term to view to the complete record​, subheadings, broader and narrower terms. 

Build a search from the results list or from the MeSH term record to specify subheadings.

  • Select the box next to the MeSH term or subheadings that you wish to search and click Add to Search Builder.
  • ​You may need to switch AND to OR, depending on how you would like to combine terms.
  • Repeat the above steps to add additional MeSH terms. When your search is ready, click Search PubMed.

Logic Grid with Keywords and Index Terms or Subject Headings from Systematic Reviews: Constructing a Search Strategy and Searching for Evidence.

Review sample policy paper: Office of Environmental Health Hazard Assessment (OEHHA.) 2021. Health effects assessment: potential neurobehavioral effects of synthetic food dyes in children. 

See search strategy details on page 31.

complex search strategy details for each PECO component, including title/abstract, medical subject headings and other tags.