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19 Cards in this Set
- Front
- Back
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T or F: In observational studies, it is safer to accept a treatment proven to be harmless/useless, than it is to accept a treatment proven to be effective.
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TRUE.
In Observational studies treatments can not be controlled, and therefore are not 100% free of errors, or confounders. |
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a drop out rate of _____ or more is not a good study.
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20% or more
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"intention to treat" analysis
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data for everyone who was randomized to treatment, even if they didn’t complete
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What is the drop out rate?
118 participants 90 completed treatment |
90/118 = 0.763
1 - (0.763) = 0.237 or 23.7% Drop Out |
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Relative Risk Reduction (RRR)=
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CER – EER/ CER
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Disadvantages of using RRR
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-Doesn’t reflect how common the event is without therapy (baseline risk or CER)
-Doesn’t discriminate between large and small effects -NOT a good # to use. |
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Absolute Risk Reduction (ARR) =
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Risk in control group minus risk in treated group
ARR= CER - EER |
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# Needed to treat (NNT) definition
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# of patients you would need to treat with the experimental therapy to prevent one additional bad outcome, or achieve one additional favorable outcome
-Typically includes time period |
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NNT =
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1/ ARR
- ex: ARR= 18.7%... If give vaccine to 19 people, likely to prevent 1 person from getting flu next year. |
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T or F: smaller NNTs are more impressive.
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TRUE
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Odds Ratio (OR) definition
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The odds of an event are calculated as the number of events divided by the number of non-events
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OR =
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Ratio of odds for exposed group divided by odds for not exposed group
P1/(1-P1) / P2/(1-P2) |
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T or F: When events are rare, risks and odds are very similar
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TRUE
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Where are ORs used?
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- used in case control studies where disease prevalence is not known.
-In systematic reviews, because of mathematical properties (zero to infinity) |
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In clinical trails when looking for benefit expect OR to be...
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<1.
OR= 1 means no difference between groups. |
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Systematic review definition
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A summary of the medical literature that uses explicit methods to systematically search, critically appraise, and synthesize the world literature on a specific issue
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Goal of systematic reviews is to...
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reduce bias and random error
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Meta analysis
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a systematic review that uses quantitative statistical methods to summarize the results of research (combining the results of individual studies), preferably randomized controlled trials
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Number Needed to Harm (NNH)=
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# of patients you would need to expose to a harmful entity to produce one additional harmful outcome
- For RCT and cohort studies, NNH = 1/RR - For Case-control studies, NNH is based on Patient Expected Event Rate (PEER) |
