PPT-Sample Size Excel GrowingKnowing.com © 2011

1 GrowingKnowingcom 2011 Sample size How big should a sample be for a valid study Why phone 10000 students if phoning 50 is enough Large samples take longer and cost more What if a sample of 50 is not enough you need 51 for a valid study. Study Design and Sample Size. Ideally we are involved in a study from the beginning. As statisticians (an epidemiologist) part of our role is to ensure the study is designed to address the primary hypothesis under consideration. Jed Friedman, World . Bank. SIEF Regional Impact Evaluation Workshop. Beijing, China. July 2009. Adapted from slides by Esther . Duflo. , J-PAL. Planning Sample Size for . Randomized Evaluations. General question: . Presented by :Dr. . Reshma.S. . Moderator : Dr. . Subodh. S Gupta. Why do we need sample size calculation?. When should we calculate sample size?. Basic principles for sample size calculation. Derivation of sample size formula. Excel. GrowingKnowing.com © 2011. 1. GrowingKnowing.com © 2011. Estimates. We are often asked to predict the future!. When will you complete your team project?. When will you make your first million dollars?. Excel. GrowingKnowing.com © 2011. 1. GrowingKnowing.com © 2011. There are 5 steps. Step 1: State the null and alternative hypothesis. Step 2: Select a confidence level. Step 3: Determine the decision rule. Excel. GrowingKnowing.com © 2011. 1. GrowingKnowing.com © 2011. Sample size. How big should a sample be for a valid study?. Why phone 10,000 students if phoning 50 is enough?. Large samples take longer and cost more. Manual. GrowingKnowing.com © 2011. 1. GrowingKnowing.com © 2011. Sample size. How big should a sample be for a valid study?. Why phone 10,000 students if phoning 50 is enough?. Large samples take longer and cost more. GrowingKnowing.com © 2011. 1. GrowingKnowing.com © 2011. Binomial probabilities. Your choice is between success and failure. You toss a coin and want it to come up tails. Tails is success, heads is failure. 1. GrowingKnowing.com © 2011. Percentile. What ‘s the difference between percentile and percent?. Percent measures ratio. 90% . percent . on a test shows you got 9 out 10 questions right. . Percentile measures position. 1. GrowingKnowing.com © 2011. Small Samples. If your sample size is below 30, this is a small sample so use the t table, not z.. Decision rule uses =. t.inv. instead of =. normsinv. Excel 2010: . GrowingKnowing.com © 2011. 1. GrowingKnowing.com © 2011. Estimates. We are often asked to predict the future!. When will you complete your team project?. When will you make your first million dollars?. 1. Sampling. A . sample. is a subset of the . population. In a . sample. , you study a few members of the population. In a . census. , you study every member of the population. If done properly, a sample can be accurate and avoid the cost and time needed for a full census . 1. GrowingKnowing.com © 2011. Binomial probabilities. Your choice is between success and failure. You toss a coin and want it to come up tails. Tails is success, heads is failure. Although you have only 2 conditions: success or failure, it does not mean you are restricted to 2 events. Review of Type I & Type II Errors. When we conduct a test of any hypothesis regardless of the test used we make one of two possible decisions:. Reject the null (H. o. ) in favor of the alternative (H.