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st: New version of -powercal- on SSC

From   "Roger B. Newson" <>
To   "" <>
Subject   st: New version of -powercal- on SSC
Date   Mon, 02 Apr 2012 12:14:37 +0100

Thanks as always to Kit Baum, a new version of the -powercal- package is now downloadable from SSC. In Stata, use the -ssc- command to do this, or -adoupdate- if you already have an old version of -powercal-.

The -powercal- package is described as below on my website, and performs power and sample size calculations in a dataset with 1 observation per scenario, calculating any of the 5 quantities power, alpha, detectable difference, sample size, and the standard deviation of the influence function from the other 4 quantities in the scenario, and storing the result in a new variable. This allows the user to produce power and sample size curves, rather than just point estimates. The new version is updated to Stata Version 10, and the examples in the online help, and in the .pdf manual, no longer use the old Stata Version 7 -graph- command. There is also a hypertext, in the online help, which directs the user to my 2004 Stata Journal article on -powercal- (Newson, 2004), which can now be downloaded free and gives a full set of methods and formulas.

Users of Stata Versions 7, 8 and 9 can still download the old Stata Version 7 version of -powercal- from my website by typing, in Stata,

net from

and selecting and installing -powercal-.

Best wishes



Newson R. 2004. Generalized power calculations for generalized linear models and more. The Stata Journal 4(4): 379-401. Download from The Stata Journal website at

Roger B Newson BSc MSc DPhil
Lecturer in Medical Statistics
Respiratory Epidemiology and Public Health Group
National Heart and Lung Institute
Imperial College London
Royal Brompton Campus
Room 33, Emmanuel Kaye Building
1B Manresa Road
London SW3 6LR
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Web page:
Departmental Web page:

Opinions expressed are those of the author, not of the institution.

package powercal from

      powercal: Generalized power calculations saving results in variables

powercal performs general power calculations, storing the result in a new variable, which can be plotted and/or listed. It can calculate any of 5 quantities, namely number of sampling units, power, alpha (significance
      level), delta (difference in parameter value to be detected), or the
standard deviation (SD) of the influence function, defined as the standard error multiplied by the square root of the sample number. Each of these 5 quantities is calculated using user-defined expressions for the other 4, usually involving existing variables supplied by the user. powercal has 2 advantages over sampsi. First, it performs general power calculations, not only power calculations for special cases such as differences between means and proportions. Second, it stores the results in variables, which
      the user can list and/or plot on graphs. This package has an on-line
manual powercal.pdf containing the Methods and Formulas and details on
      the Examples in the help file.

      Author: Roger Newson
      Distribution-Date: 26march2012
      Stata-Version: 10

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