UMEM Educational Pearls - By Mike Witting

Needed for sample size determination

Power – (1-beta), where beta is the risk of a type 2 error – rejecting the accepting the null hypothesis when it is true – this is usually selected to be 0.8 or 0.9.

Significance (alpha), the chance of making a type 1 error – accepting the alternate hypothesis when the null hypothesis is true. This is usually selected to be 0.05.

One-tailed or two-tailed – is the null hypothesis one of no difference (experimental arm not better or worse) or one-sided (experimental arm not better)?

Effect Size. This is the challenging part. This is the size of the difference in outcomes you’re looking for. 

  For continuous outcomes (example – difference in pain scores). You’ll need an estimate for the variation in the scores between presentations, or the standard deviation. You can get this from a literature estimate or a from small local measurement, say of 10 patients or so.

  For a dichotomous outcome (example – percentage of successes), you can usually estimate the percentage in one group and choose the difference you are looking for.

The effect size has a big effect on the sample size. Generally, cutting the effect size in half increases the sample size by fourfold.

Statistical software - next pearl.

Category: Misc

Title: PICO for Research Question

Keywords: Research Question (PubMed Search)

Posted: 5/20/2024 by Mike Witting, MD
Click here to contact Mike Witting, MD

Starting a study? Frame your research question in the PICO format:

Patients (consider severity of presentation, setting, demographics)

Intervention (either something you propose or something in use)

Comparison (another group, the same group without intervention, or a benchmark)

Outcome (a measurement)

This classic format has been used to evaluate studies, as in Journal Club (by our esteemed Dr. Wilkerson), as a literature search tool, or by the Cochrane review. 

Starting with a PICO research question can help you narrow your focus and maintain it.

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Category: Misc

Title: Research Pearl - FINER Criteria for New Studies

Posted: 3/12/2024 by Mike Witting, MD (Emailed: 3/28/2024) (Updated: 3/28/2024)
Click here to contact Mike Witting, MD

Considering starting a research project? Apply the FINER criteria:


                  Do you have the resources to study this? Enough patients? Support?


                  Does it interest you enough to devote your time to it? Does it interest colleagues?


                  Would it provide new findings, or confirm, refute, or extend prior findings?


                  Can you think of a way to ethically study it?


                  Consider possible outcomes of your research. Could the study advance care or policy?

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