Friday, 18 April 2014

Sample Size and Power Determination

"How many subjects do I need?" is a common question from researchers.  "It depends" is the common, unsatisfactory, response.  Learn what the answer depends on in Thomas Ryan's online course, “Sample Size and Power Determination,” at
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"Sample Size and Power Determination" covers how to plan the appropriate sample size for a study, striking the optimal balance of feasible sample size, reasonable assumptions, and acceptable power. The power of a study (the study's ability to prove a treatment effect exists) is determined by such factors as the magnitude of the treatment effect, the sample size, alpha (the level of statistical significance required), and (for survival studies) the study duration.

Since some of these factors are under the researcher's control while others are not, the goal of power analysis is to balance them as a series of "What if's." For example "What sample size would we need if the treatment reduces the risk of death by 10%, and what sample size would we need if the treatment reduces the risk of death by 20%?" Or, "How would power be affected if the study followed patients for two years rather than three?" This process of finding a balance among factors is done most effectively with graphs that allow the researcher to grasp (and communicate) a range of options in a single picture, and find the one that strikes the optimal balance of feasible sample size, reasonable assumptions, and acceptable power.  Illustrations include examples from means, proportions, correlations, and survival analysis, and possibly from other procedures as well.

Course Program:
Course outline: The course is structured as follows

SESSION 1: Introduction to Sample Size Determination and Power, Including Useful Software
  • Hypothesis tests and confidence intervals
  • Factors that determine sample size
  • Sample size for estimating a population mean
  • Examples, including a study from the literature
  • External and internal pilot studies
  • Ways to estimate sigma
  • What should be avoided:  Retrospective power and standardized effect sizes
  • Ethical issues in power analysis
  • Recommended references
  • Software
SESSION 2: Tests on Population Means (continued)
  • T-Test or Z-Test for population mean?
  • Testing the normality assumption
  • Confidence Intervals on Power and/or Sample Size?
  • Two-sample study from the literature with unequal sample sizes
    • Sample sizes determined by scientist in two stages without software
    • Illustration of more efficient sample determination using software
  • Using coefficient of variation
  • Paired data
  • Additional examples

SESSION 3: Tests on Proportions and Variances
  • One proportion    
    • Software disagreement and rectification
  • Two proportions
  • Options, including transformations built into software, for tests of proportions
  • One variance  and two variances
  • Examples
 SESSION 4: Regression and Design
  • Simple linear regression
    • Complexity caused by what must be inputted
  • Multiple linear regression
  • Optional material:  Repeated measures designs, Logrank test for survival analysis
  • Literature references for sample size determination with more advanced
    statistical methods and some information on corresponding software
Homework in this course consists of short answer questions to test concepts and guided data analysis problems using software.
In addition to assigned readings, this course also has supplemental readings available online

Who Should Take This Course?
Anyone responsible for the planning of a study, or its subsequent analysis. Investigators writing grant applications or other proposals in which sample size must be specified.

The instructor, Dr. Thomas P. Ryan, is the author of "Sample Size and Power Determination" (Wiley, 2103), a number of other books, plus numerous papers in peer-reviewed journals.  He is an elected Fellow of the American Statistical Association, American Society for Quality, and Royal Statistical Society. Participants can ask questions and exchange comments with Dr. Ryan via a private discussion board throughout the period of the course.

You will be able to ask questions and exchange comments with the instructors via a private discussion board throughout the course.   The courses take place online at in a series of 4 weekly lessons and assignments, and require about 15 hours/week.  Participate at your own convenience; there are no set times when you must be online. You have the flexibility to work a bit every day, if that is your preference, or concentrate your work in just a couple of days.

We, the Center for eLearning and Training (C-eLT), Pune, partner with and offer these courses to Indian participants at special prices payable in INR.

For India Registration and pricing, please visit us at

Call: 020 6680 0300 / 322


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