Integrated Dentistry I Third Year

1. DENTED 371
Study designs

2. Sources of evidence
• Scientific evidence is the product of:
– Well-designed
– Well-controlled research investigation that
minimize sources of bias.
• Evidence is considered the synthesis of all
valid research studies that answer a
specific question.

3. Sources of evidence
• Historically, what were the sources of
evidence?
• What are the types of evidence-based
sources?

4. Sources of evidence
• Quantitative research
– Focuses on establishing cause and effect
relationships through testing a specific
hypothesis and reporting the results in
statistical terms.
– Experimental
– Nonexperimental

5. Sources of evidence
• Qualitative research
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– Is exploratory and uses an interpretive,
naturalistic approach that focuses on how
individuals or groups view or understand their
surroundings and construct meaning out of
their experiences,
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7. Nonexperimental studies
• Purpose and study design
– Observational studies systematically describe
and interpret conditions/relationships that
already exist.
– Examines the association between exposure
and a risk factor or between a disease and
hypothesized risk factor.
– A treatment or intervention is not given.
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8. Nonexperimental studies
• Data collection
– Gathers data without giving a treatment or
intervening to control variables.
– Clinical exams, surveys or questionnaires.
– Can be collected once or multiple times over
time.

9. Nonexperimental studies
• Role of the researcher
– Tends to remain separate from the subject
matter.

10. Nonexperimental studies
• Analysis
– Analysis occurs after all the data are
collected.
– Involves analysis of numerical data that can
be combined and manipulated using statistical
methods.
– Results reported using numerical relations
and statistical terms.

12. • Three commonly used study designs are
discussed in this lecture:
• Cross-Sectional Study
• Cohort Study
• Case Control Study

13. Cross-sectional study
• Cross-sectional study designs are used
when studying one or more variables
within a given population at one point in
time.
• Such studies are useful for establishing
associations rather than causality and for
determining prevalence, rather than
incidence.
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14. Cross-sectional study
Advantages:
• Simple and inexpensive
• Ethically safe
• Quick data collection
• Attrition is not an issue
• Holds time constant

15. Cross-sectional study
Disadvantages:
• Does not permit distinction between cause and
effect
• Recall bias susceptibility
• Confounders may be unequally distributed
between groups
• Differences may be due to age/time effects or
cohort effects
• Inter-subject variability exists, making it harder to
detect a difference
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16. Cohort study
• In cohort studies, a group of people within
a population is followed over a specified
period of time to track who experiences or
develops the same significant life event or
treatment.

17. Cohort study
• This type of design can be used "to study
incidence, causes, and prognosis.
Because they measure events in
chronological order they can be used to
distinguish between cause and effect."

18. Cohort study
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• Cohort studies can be done prospectively,
retrospectively, or using cross-sectional
methods. As well, two groups may be
followed: one containing the agent of
interest and the other acting as a control
group.
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20. Cohort study
Advantages:
• Ethically safe
• Subjects can be matched
• Can establish timing and directionality of events
• Eligibility criteria and outcome assessments can
be standardized
• Administratively easier and cheaper than
Randomized Controlled Trial
• Possible to examine multiple outcome variables
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21. Cohort study
Disadvantages:
• The time to develop the disease may be
long.
• The cost of follow up
• The potential for losing subjects over time.
• For rare disease, large sample sizes or
long follow-up necessary.

22. Case-Control study
• Most commonly carried out
retrospectively, case control studies are
used to compare cases who have a
certain condition with a control group
known not to have developed the outcome
of interest.

23. Case-Control study
• The control group is usually not only taken
from the same population base, but also
matched for age and gender. Such studies
"seek to identify possible predictors of
outcome and are useful for studying rare
disease or outcomes. They are often used
to generate hypotheses that can then be
studied via prospective cohort or other
studies"
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25. Case-Control study
Advantages:
• Quick and cheap
• Only feasible method for studying very
rare disorders or those with long lag
between exposure and outcome
• Fewer subjects needed than crosssectional studies.

26. Case-Control study
Disadvantages:
• Reliance on recall or records to determine
exposure status
• Confounders
• Selection of control groups is difficult
• Potential bias: recall, selection
• Cannot calculate the relative risk
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