{smcl}
{hline}
help for {hi:sampsi_reg}
{hline}

{title: Calculates Sample Size or Power for Simple Linear Regression}

{p 8 22}
{cmdab:sampsi_reg}
[,
{opt null(#)}
{opt alt(#)}
{opt n1(#)}
{opt sd1(#)}
{opt a:lpha(#)}
{opt p:ower(#)}
{opt s:olve(string)}
{opt sx(#)}
{opt sy(#)}
{opt var:method(string)}
{opt yxcorr(#)}
{opt onesided}
}
]

{p}

{title:Description}

{p 0 0}
{hi: 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.

{p 0 0}
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.

{p 0 0}
This command can be combined with {hi:samplesize} in order to look at multiple calculations and to plot the results.

{title:Updating this command}

{p 0 0}
To obtain the latest version click the following to uninstall the old version
{p_end}
{stata ssc uninstall sampsi_reg}
And click here to install the new version
{stata ssc install sampsi_reg}

{title:Options}

{p 0 0}
{opt null(#)} specifies the "null slope".

{p 0 0}
{opt alt(#)} specifies the "alternative slope".

{p 0 0}
{opt n1(#)} size of sample.

{p 0 0}
{opt sd1(#)} standard deviation of the residuals.

{p 0 0}
{opt a:lpha(#)} significance level of test; default is {hi:a(0.05)}.

{p 0 0}
{opt p:ower(#)} power of test; default is {hi:p(0.9)}.

{p 0 0}
{opt s:olve(string)} specifies whether to solve for the sample size or power; default is {hi:s(n)} solves for n and
the only other choice is {hi:s(power)} solves for power.

{p 0 0}
{opt sx(#)} the standard deviation of the X's.

{p 0 0}
{opt sy(#)} the standard deviation of the Y's.

{p 0 0}
{opt yxcorr(#)} the correlation between Y's and X's.

{p 0 0}
{opt var:method(string)} specifies the method for calculating the residual standard deviation. 
{opt varmethod(r)} uses the Y-X correlation and  {opt varmethod(sdy)} uses the standard deviation of the Y's,
the default uses a direct estimate of the residual sd {opt sd1(#)}. 

{p 0 0}
{opt onesided} one-sided test; default is two-sided.

{title:Examples}

{p 0 0}
Calculate power for a two-sided test:
{p_end}

{p 2 2}
{stata sampsi_reg, null(0) alt(0.25) n(100) sx(0.25) yxcorr(0.2) varmethod(r) s(power)}

{p 0 0}
Compute sample size:

{p 2 2}
{stata sampsi_reg, null(0) alt(0.25) sx(0.25) sy(1) varmethod(r) s(n)}

When specifying the variance of the y's you must have a {opt varmethod} option
{p 2 2}
WRONG: {stata sampsi_reg, null(0) alt(5) sx(0.5) sy(12.3)}{p_end}
{p 2 2}
CORRECT: {stata sampsi_reg, null(0) alt(5) sx(0.5) sy(12.3) var(sdy)}

{title:Author}

{p}
Adrian Mander, MRC Biostatistics Unit, Cambridge, UK.

Email {browse "mailto:adrian.mander@mrc-bsu.cam.ac.uk":adrian.mander@mrc-bsu.cam.ac.uk}

{title:See Also}
Related commands:

{p 2 2}
{help sampsi}, {help samplesize} (if installed), {help sampclus} (if installed), {help xsampsi} (if installed), {help artmenu} (if installed)