{smcl} {* *! version 1.0 14 Mar 2019}{...} {vieweralsosee "" "--"}{...} {vieweralsosee "Install command2" "ssc install command2"}{...} {vieweralsosee "Help command2 (if installed)" "help command2"}{...} {viewerjumpto "Syntax" "sampsi_reg##syntax"}{...} {viewerjumpto "Description" "sampsi_reg##description"}{...} {viewerjumpto "Options" "sampsi_reg##options"}{...} {viewerjumpto "Remarks" "sampsi_reg##remarks"}{...} {viewerjumpto "Examples" "sampsi_reg##examples"}{...} {title:Title} {phang} {bf:sampsi_reg} {hline 2} Calculates Sample Size or Power for Simple Linear Regression {marker syntax}{...} {title:Syntax} {p 8 17 2} {cmdab:sampsi_reg} [{help varlist}] [{cmd:,} {it:options}] {synoptset 20 tabbed}{...} {synopthdr} {synoptline} {syntab:Main} {synopt:{opt null(#)}} specifies the "null slope". {pstd} {p_end} {synopt:{opt alt(#)}} specifies the "alternative slope". {pstd} {p_end} {synopt:{opt n:1(#)}} size of sample. {pstd} {p_end} {synopt:{opt sd:1(#)}} standard deviation of the residuals. {pstd} {p_end} {synopt:{opt a:lpha(#)}} significance level of test. {pstd} {p_end} {synopt:{opt p:ower(#)}} power of test. {pstd} {p_end} {synopt:{opt s:olve(string)}} specifies whether to solve for the sample size or power; default is s(n) solves for n and the only other choice is s(power) solves for power. {p_end} {synopt:{opt onesided}} one-sided test; default is two-sided. {pstd} {p_end} {synopt:{opt sx(#)}} the standard deviation of the X's. {pstd} {p_end} {synopt:{opt sy(#)}} the standard deviation of the Y's. {pstd} {p_end} {synopt:{opt var:method(string)}} specifies the method for calculating the residual standard deviation. varmethod(r) uses the Y-X correlation and varmethod(sdy) uses the standard deviation of the Y's, the default uses a direct estimate of the residual sd sd1(#). {p_end} {synopt:{opt yxcorr(#)}} the correlation between Y's and X's. {pstd} {p_end} {synoptline} {p2colreset}{...} {p 4 6 2} {marker description}{...} {title:Description} {pstd} {pstd} {cmd:sampsi_reg} calculates the power and sample size for a simple linear regression. The theory behind this command is described in Dupont and Plummer (1998) Power and Sample Size Calculations for Studies involving Linear Regression, Controlled Clinical Trials 19:589-601. {pstd} The calculations require an estimate of the residual standard error. There are three methods for doing this: enter the estimate directly; enter the standard deviation of the Y's; or enter the correlation between Y and X values. {pstd} This command can be combined with samplesize in order to look at multiple calculations and to plot the results. {pstd} {marker options}{...} {title:Options} {dlgtab:Main} {phang} {opt null(#)} specifies the "null slope". {pstd} {p_end} {phang} {opt alt(#)} specifies the "alternative slope". {pstd} {p_end} {phang} {opt n:1(#)} size of sample. {pstd} {p_end} {phang} {opt sd:1(#)} standard deviation of the residuals. {pstd} {p_end} {phang} {opt a:lpha(#)} significance level of test. {pstd} {p_end} {phang} {opt p:ower(#)} power of test. {pstd} {p_end} {phang} {opt s:olve(string)} specifies whether to solve for the sample size or power; default is s(n) solves for n and the only other choice is s(power) solves for power. {p_end} {phang} {opt onesided} one-sided test; default is two-sided. {pstd} {p_end} {phang} {opt sx(#)} the standard deviation of the X's. {pstd} {p_end} {phang} {opt sy(#)} the standard deviation of the Y's. {pstd} {p_end} {phang} {opt var:method(string)} specifies the method for calculating the residual standard deviation. varmethod(r) uses the Y-X correlation and varmethod(sdy) uses the standard deviation of the Y's, the default uses a direct estimate of the residual sd sd1(#). {p_end} {phang} {opt yxcorr(#)} the correlation between Y's and X's. {pstd} {p_end} {marker examples}{...} {title:Examples} {pstd} {pstd} {pstd} Calculate power for a two-sided test: {pstd} {stata sampsi_reg, null(0) alt(0.25) n(100) sx(0.25) yxcorr(0.2) varmethod(r) s(power)} {pstd} Compute sample size: {pstd} {stata sampsi_reg, null(0) alt(0.25) sx(0.25) sy(1) varmethod(r) s(n)} {pstd} When specifying the variance of the y's you must have a varmethod option WRONG: {stata sampsi_reg, null(0) alt(5) sx(0.5) sy(12.3)} CORRECT: {stata sampsi_reg, null(0) alt(5) sx(0.5) sy(12.3) var(sdy)} {pstd} {title:Stored results} {synoptset 15 tabbed}{...} {p2col 5 15 19 2: Locals}{p_end} {synopt:{cmd:r(power)}} the power {p_end} {synopt:{cmd:r(N_1)}} the first arm sample size {p_end} {synopt:{cmd:r(N_2)}} the second arm sample size {p_end} {title:Author} {p} Dr Adrian Mander, MRC Biostatistics Unit, University of Cambridge. Email {browse "mailto:adrian.mander@mrc-bsu.cam.ac.uk":adrian.mander@mrc-bsu.cam.ac.uk} {title:See Also} Related commands: {help samplesize} (if installed){stata ssc install samplesize} (to install this command) {help sampsi_fleming} (if installed) {stata ssc install sampsi_fleming} (to install this command) {help simon2stage} (if installed) {stata ssc install simon2stage} (to install this command)