Bandit Thinkhamrop, PhD.(Statistics)

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Biostatistics for Critical Appraisal

• Bandit Thinkhamrop, PhD.(Statistics)
• Dept. of Biostatistics Demography
• Faculty of Public Health
• Khon Kaen University

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Core Questions

1. What is the research question?
2. What is the answer or the conclusion?
3. What is the magnitude of effect being used as the
   basis of the conclusion?
4. How large is the effect conclusive or not?
5. How likely is the validity of the magnitude of
   effect - accurate, over or under estimate,
   questionable, unassessable?
6. Can the conclusion be acceptable? Why?
7. How this paper could be improved?

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1. What is the research question?

• State the research question
• Focus on the primary research question or the one
  that lead to the main conclusion
• Example
• What are predictors of low birth weight?
• What is the efficacy of the HIV vaccine?

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2. What is the answer or the conclusion?

• Extract the answer to the primary research
  question
• Usually be obtained from the main conclusion of
  the study
• Example
• Low BMI of mother and not received ANC increase
  risk of low birth weight
• HIV vaccine can prevent HIV infection

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3. What is the magnitude of effect being used as
the basis of the conclusion?

• If reported, transcribe it. If not, calculate it
  based on the reported results.
• Its the 95CI is essential
• Summarize the magnitude of effect as a forest
  plot-like diagram against the meaningful level is
  recommended
• Example
• OR (95CI) of each factor on low birth weight
  Low BMI of mother (OR 3.2 2.50 to 4.50), and
  not received ANC increase risk of low birth
  weight (OR 1.6 1.02 to 2.18)
• HIV vaccine efficacy is 30 (95CI 1.1 to
  52.2)

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Forest plot for the Difference
Minimum meaningful level
Male (0.9 0.1 to 1.7)
Female (1.4 -0.1 to 2.9)
Overall (1.8 0.6 to 3.0)
Flavor Intervention A
Flavor Intervention B
?
?
1
-1
0
2
3
-2
-3
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Forest plot for RR, IRR, OR, HR
Minimum meaningful level
Low BMI of mother (3.20 2.50 to 4.50)
Received ANC (1.60 1.02 to 2.18)
Protective effect
Risk effect
?
0
2
0.50
1
3
4
0.33
0.25
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Notice the wrong scale
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4. How large is the effect conclusive or not?

• Compare the magnitude of both lower and upper
  boundary of the 95CI with the meaningful level
  of effect
• To be conclusive, the CI needs NOT include the
  meaningful cut point
• Conclusive findings imply sufficient sample size

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5. How likely is the validity of the magnitude of
effect- accurate, over or under estimate,
questionable, unassessable?

• Describe briefly how the magnitude of effect was
  obtained
• Describe how it could be wrong by considering
  these three issues
• Wrong data?
• Selection bias
• Information bias
• Confounding bias
• Wrong analysis?
• Applied inappropriate statistical method
• Poor or unclear reporting
• Important information was not provided

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6. Can the conclusion be acceptable?

• Answer Yes/No and Why?
• Explain the mechanisms as to how the magnitude of
  effect could be wrong, if not accepted
• Elaborate more by describing what position of
  this evidence in your evidence-base practice

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7. How this paper could be improved?

• No research is perfect there are rooms to
  improve.
• Go beyond what had been reported in the paper to
  what should have been done to be better under
  unlimited resources