 ## SAMPLE SIZE AND POWER ANALYSIS CALCULATOR AND GRAPHER

Health Decision Strategies, LLC.

Data Entry Page
--  Beta version, for demonstration only -

 Enter data in yellow boxes, hit "submit button" and answers will appear on the next page in blue boxes -- graphs of data below. WTP_1 WTP_2 WTP_3 WTP_4 WTP_5 WTP Threshold --> Z (alpha/2)= Z value for probability <-- Prob of type I error (alpha) Z (beta)= Z value for probability of Type II error <-- Prob of type II error (beta) sdet= standard deviation of the effect in treatment group sdec= standard deviation of the effect in control group sdct= standard deviation of the cost in treatment group sdcc= standard deviation of the cost in control group dC= mean difference in cost dE= mean difference in effect Corr_dEdC correlation between difference in cost and difference in effect Sample Size Calculator - Results - number needed in each arm based on data entered above. WTP_1 WTP_2 WTP_3 WTP_4 WTP_5 N = Power Analysis If the study has already been completed, this section below calculates the power to detect a difference, if a difference actually exists, based on the numbers entered in the first group of yellow boxes above. N_1 N_2 N_3 N_4 N_5 Study Sample 1-Z_beta Power = (prob(1-Z_beta)) Figure 1. Below is a graph example illustrating the data results generated by the HDS sample size calculator.This shows the sample size by willingness to pay and by different values of the correlation between cost and effect. Note the "effect only" line which is constant. Figure 2. Below is a graph example illustrating the data results generated by the HDS sample size calculator.This shows the sample size by willingness to pay and by different values of power. Note the "effect only" line which is constant. Figure 3. Below is a graph example illustrating the data results generated by the HDS power calculator.This shows the power by sample size for different values of the correlation between cost and effect. References: Briggs A and Gray A. Power and sample size calculations for stochastic cost-effectiveness analysis. Med Decis Making 1998: 18 suppl:S81-S92. Briggs A and Tambour M. The design and analysis of stochastic cost-effectiveness studies for the evaluation of health care interventionsl. Stockholm School of Economics. Working paper #234. April 1998. Walter SD et al. Estimation, power and sample size calculations for stochastic cost and effectiveness analysis. Pharmacoeconomics 2007; 25(6):455-466. Glick H et al. Economic evaluation in clinical trials. Oxford University Press, 2007.