Statistical power and variance of effect size
Within the current clinical context, will the outcome have limited or extensive variance in the population?
If an effect size is highly varied (wide 95% confidence intervals for proportions or large standard deviations associated with means), then more observations of the outcome will be needed to detect significant effects in the diverse and heterogeneous population.
If the effect size has little variation (narrow 95% confidence intervals for proportions or small standard deviations associated with means), then less observations of the outcome will be needed to detect statistical significance.
It is often a good practice to overestimate the variance of an effect size. This overestimation forces researchers to collect more observations of the outcome, just in case the hypothesized magnitude of the effect size is smaller than expected. These extra observations of the outcome will also deter Type II errors associated with smaller sample sizes.
The need to hypothesize the variance of effect sizes further reinforces the use of evidence-based measures of effect when conducting a priori sample size calculations. The values reported in the literature often have more credibility and validity.
How much variance is hypothesized to exist in the outcome of interest?
Statistician Services for Students
Eric Heidel, Ph.D. will provide the following services for undergraduate and graduate students at $50/hour. Secure checkout is available with Stripe or PayPal.
- Statistical Analysis
- Research Design
- Sample Size Calculations
- Diagnostic Testing and Epidemiological Calculations
- Survey Design and Psychometrics
AppNotch: Convert this website into an Android and iOS app.
AppNotch team will notify you when your app gets approved in Google Play and Apple iTunes App Stores. Once your app goes live, enter your App Store URLs in this property window, publish your Weebly site and your app store icons will be visible in this page.
Please visit AppNotch.com FAQ to learn more about how to add App Store icons to your website, update your app, send Push notifications and more.
Professional Statistician For Hire!
Copyright © 2019 Scalë. All Rights Reserved. Patent Pending.