Reading the Dental LIterature
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Transcript Reading the Dental LIterature
A Brief Guide to Critical Literature Review
Cathy Hollister, RDH, MSPH, PhD
Nashville Area Dental Support Center
Session Goal
To review key concepts in interpreting current, relevant
dental research so that clinicians can use
appropriate publications for clinical decision making.
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
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
Are the results statistically significant?
2. Are the results clinically significant?
1.
What is the Publication Type?
Research
Reviews
Commentary
(Primary)
(Secondary)
(Secondary)
Experiments
Standard Review
Editorial
QuasiExperimental
(quantitative)
Systematic
Review
Opinion/Position
Descriptive
Qualitative
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
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
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
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
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
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
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?
Primary Research
Key Points to Consider
Study Design
Validity
Internal
External
Statistics
What is the Study Design?
Experiments
Randomized
Clinical Trials
PretestInterventionPosttest
QuasiExperimental
Descriptive
Qualitative
Cohort
Epidemiological
Surveys
Ethnography or
Phenomenology
Case Control
Surveillance
Grounded
Theory
Cross Sectional
Single or
multiple case
studies
Time or Case
Series
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
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
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
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
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?
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
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?
Internal Validity
Did the study
measure what was
intended?
Bias
Even with the best
study design, sources
of bias may be
unavoidable and may
affect study’s impact
Confounders
Causal
Relationships
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?
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.
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.
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<.05 means that ,“There is less than a
5% probability that the study findings happened by
chance and chance alone.”
p<.01 means, “There is less that 1% probability that
the findings are due to chance and chance alone.”
Clinical vs Statistical Significance
If the results of the study reach statistical
significance, consider if the finding is really important
clinically
Example:
A periodontal intervention reduced pocket depth by
0.03mm (p<.01) (Statistically significant, or the result
was due to the intervention and not a result of normal
variation among the study participants)
Is a gain of 0.03mm important to periodontal health?
(Clinically significant)
Summary
Every scientific publication has weaknesses, no
clinical question can be answered by a single study
or article
Repeated results lend strength to conclusions
Consider the differences between the study
population and YOUR population
Statistical significance may not mean clinical
significance
Questions?