A Brief Guide to Critical Literature Review Cathy Hollister,
RDH, MSPH, PhD Nashville Area Dental Support Center
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Session Goal To review key concepts in interpreting current,
relevant dental research so that clinicians can use appropriate
publications for clinical decision making.
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Learning Objectives At the end of this session, participants
will be able to: Name a strength and weakness of review articles
and original research reports Explain the benefits of a
quasi-experimental study design Explain the importance of internal
and external validity Interpret a p value
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Key Points to Consider: Peer Reviewed Publications 1. Is the
material primary or secondary? 2. What was the study design? 3.
Internal Validity: does the study measure want was intended 4.
External Validity: can the results be generalized 5. Statistics 1.
Are the results statistically significant? 2. Are the results
clinically significant?
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What is the Publication Type? Research (Primary) Experiments
Quasi- Experimental (quantitative) DescriptiveQualitative Reviews
(Secondary) Standard Review Systematic Review Commentary
(Secondary) EditorialOpinion/Position
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Primary Research Strengths Includes a full description of
research Focused Controls for confounding variables (the ability to
control for other variables differs by study design) Weaknesses
Scope is limited May not be generalizable to other populations or
times
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Review Articles Strengths Includes relevant material from many
types of studies Presents studies conducted over a period of time
Weaknesses The reader may be unable to evaluate appropriateness of
the articles included in the review May present only one point of
view
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Review Article Consider the review article: Mercury Toxicity
and Treatment: A review of the literature Notice the lack of strict
criteria that opens the possibility of author bias to stress a
particular point of view Notice also that for the reader, it can be
very difficult to evaluate the quality of the reviewed articles
Overall conclusion: Mercury is toxic
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Systematic Reviews A specific type of review article that has
strict inclusion criteria resulting in: Only high quality research
is included Selection bias is reduced
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Systematic Review The Cochrane Collaboration conducts
systematic reviews on a variety of topics. Weakness Few studies
meet inclusion criteria, therefore it can be difficult to draw
strong conclusions Example: Dental Amalgam and Multiple Sclerosis:
A Systematic Review and Meta-Analysis Overall Conclusion:
Insufficient evidence, need more study
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Original Research Now consider Neurobehavioral Effects of
Dental Amalgam in Children This Randomized Clinical Trial measured
the impact of mercury exposure in dental amalgam on neurobehavioral
assessments. Notice the narrow focus of the research and the
specific means of measuring the impact of mercury exposure. Overall
conclusion: Dental amalgam poses no significant neurobehavioral
risk in children over the age of 7 in Portugal
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3 Articles: Different Conclusions These articles had a common
topic: dental amalgam and the possible consequences to exposure to
mercury These were all published in peer reviewed journals Consider
the similarities and differences in the conclusions. What would you
consider to be a strength and weakness of each article? What
overall conclusions could you draw after reading these 3
publications?
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Primary Research Key Points to Consider Study Design Validity
Internal External Statistics
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What is the Study Design? Experiments Randomized Clinical
Trials Pretest- Intervention- Posttest Quasi- Experimental
CohortCase Control Time or Case Series Descriptive Epidemiological
Surveys Surveillance Cross Sectional Qualitative Ethnography or
Phenomenology Grounded Theory Single or multiple case studies
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Experiments:RCT Strengths Determines Causality Risk of other
factors is minimized Determines dose response Weaknesses Expensive
May be unethical May have small sample sizes May not replicate real
life situations
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Quasi-Experimental Design Cohort A group with similar
characteristics followed through time Case Control Identify people
with a condition (cases) and very similar people without the
condition (controls) Compare previous exposures Time Series
Multiple cross sectional surveys
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Quasi-Experimental Design Strengths Less expensive Avoids
ethical concerns More likely to replicate real situations
Weaknesses Usually includes biases Many variables not under strict
control Confounding variables may not be eliminated
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Confounders: Crime & Ice Cream Crime increases in the
summer Ice cream consumption increases in the summer Therefore:
Eating ice cream causes crime OR Criminals like ice cream
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Article Review: Maternal Amalgam Study design, Validity,
Statistical significance, clinical significance Are the conclusions
are supported by the data? Potential sources of bias? Are there
confounders? What can you learn from this study? What questions ARE
NOT answered in this study?
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Study Design Descriptive, observational Retrospective (to
determine previous exposures) Strengths Reflects real life
situation Inexpensive and no ethical concerns Weaknesses Cannot
determine causality Bias and confounders
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Validity: Internal and External Internal Is the study free from
bias? Did the study measure what was intended? External Can you
generalize the results to other groups?
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Internal Validity Did the study measure what was intended? Even
with the best study design, sources of bias may be unavoidable and
may affect studys impact Bias Causal Relationships Confounders
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Common Threats to Internal Validity Selection Bias: some
participants were systematically excluded from the study
Measurement error: study does not measure what was intended to be
measured Recall Bias: people do not remember past events accurately
Ambiguity about the direction of the causal relationship: Which
came first, chicken or egg?
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External Validity How generalizable are the results of the
study? Even with excellent internal validity, the results may not
be applicable to your population of interest due to systematic
differences. Example: Race, gender, and socioeconomic status are
common risk factors for many diseases. Results of a periodontal
study on healthy adults may not apply to adults with diabetes.
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Probability Statistics are based on probability. Some natural
variation will always occur within groups. Statistics are used to
test the likelihood that findings are the result of the
intervention and not a result of this natural variation. Statistics
are used to project if similar findings would occur in any other
sample or in the overall population.
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P Value A p value is a measure of the likelihood that the
results of the study happened BECAUSE of the intervention, and not
because of normal variations in the study group. The smaller the p
value, the more significant the finding. A report of p
