Post on 07-Jul-2015
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Critically Appraising a Harm Study- Part 1
Terry Shaneyfelt, MD, MPH
Associate Professor of Medicine
UAB School of Medicine
ebmteacher.com
Appraising harm studies: 3 steps
1. Are the results valid?
2. What are the results?
3. Will they help me
care for my patients?
1. In a cohort study were there clearly defined groups of patients similar in all important ways other than the exposure of interest?
2. In a case-control study did the cases and controls have a similar chance of being exposed in the past to the factor of interest?
3. Were exposures and outcomes measured the same way in both groups?
4. Was follow-up sufficiently long and complete?
Are The Results Valid?
• Patients in each cohort should be similar for prognostic factors that are known to be assocwith the outcome
• Look at Table 1
• If imbalances are seen….
1. Are they important?
2. Are they dealt with in some way?
3. What else is missing?
1) In a cohort study were the groups similar at the start of the study except for exposure?
Watch my other videos on…
• 3 questions:
1. Are the differences important?– Yes!
2. Were they adjusted for?– Yes
3. Residual confounding? – Likely
1) Were the NHS cohorts
similar?
• Both cases and control should have equal opportunity of being exposed
• Controls:• Should meet same inclusion/exclusion criteria
• Should be at risk for developing the outcome (could become a case)
• What about this study?– Is HRT associated with uterine cancer?
– Cases: women with uterine cancer
– Controls: men without uterine cancer
In a case-control study did the cases and controls have a similar chance of being exposed in the
past to the factor of interest?
Please watch Part 2 of Critically Appraising a Therapy Study
Critically Appraising a Harm Study- Part 2
Terry Shaneyfelt, MD, MPH
Associate Professor of Medicine
UAB School of Medicine
ebmteacher.com
1. In a cohort study were there clearly defined groups of patients similar in all important ways other than the exposure of interest?
2. In a case-control study did the cases and controls have a similar chance of being exposed in the past to the factor of interest?
3. Were exposures and outcomes measured the same way in both groups?
4. Was follow-up sufficiently long and complete?
Are The Results Valid?
• Investigators report a 3-fold increase in risk of melanoma in individuals working with radioactive materials
– What if physicians, concerned about a possible risk, searched more diligently in those exposed to radiation than those who weren't?
• Researchers should:
– Be blinded to exposure status (cohort studies) and to outcome status and hypothesis (case-control studies)
– Use same methods in both groups (standardized)
3) Were exposures and outcomes measured the same way in both groups?
Sources of Exposure Information
• Pre-existing Records• Inexpensive, available,
unbiased
• May be incomplete
• Interviews & Questionnaires (Patients, MDs, Family)
• Complete data
• Bias (e.g. recall bias)
• Proxy Measures (e.g. Job title, Proximity)
• Inaccurate
• Direct Measurement
• Current, future
3) Were exposures and outcomes
measured the same way in both groups?
• Follow-up needs to be long enough for participants to develop the outcome(s) of interest
• Ideally no patients are lost to follow-up
• Loss to f/u can introduce bias if – Those who are lost have different outcomes
– Differences in f/u between exposed and unexposed cohorts
4) Was follow-up sufficiently long and complete?
4) Was follow-up sufficiently long and complete?
• Moderate risk for bias (residual confounding)- in hindsight!
• Options:
– Read the results and realize the findings might not be accurate
– Find another study
–
Assessment of the NHS