University of Sheffield Department of Probability and StatisticsDepartment of Probability and Statistics

PAS6012/PAS361 Medical Statistics

Sample Size Programmes

There are a variety of programmes available for sample size / power calculations. Some of these are expensive and others are free. A widely used one within the biopharmaceutical industry is nQuery Advisor 4.0 which has many facilities not found elsewhere. A link to some of them, including those which can be run from the Web, is given on the Medical Statisticians in Sheffield page. Others you might try ones such as this calculator (which works on-line) and a programme that can be downloaded from the Vanderbilt medical Center this claims ot have facilities for linear regression and case-control studies. For more esoteric situations it is worth searching on Google with appropriate key words, e.g. for logistic regression or cluster randomized trials it is easy to find facilities that apparently give the the appropriate calculations. However, remeber that these can be placed on the web by anybody and their is no guarantee of their reliability. The ones linked here are facilities at well-known reputable places.

In this directory you will find an 'in-house' programme POWER.EXE and if you want to use it then read the README1st file. Many similar facilities are available in the programme Sample Size written by Machin & Campbell et al (1997) which comes with the tables listed in the course booklet for PAS361. In fact the programme POWER is based on the first edition of these tables; the 1997 version provides many more facilities and is modestly priced.

The DOS programme POWER.EXE is written by Dave Robson. We are making it available to you on the understanding that it is for your own personal academic related use only --- in particular that you do not give a copy of it to anybody else (even if they have 'lost' their original one), that you do not use it for commercial use (e.g. after you have left here and gone on to work for a commercial company). It comes with the usual disclaimer that whilst we believe it to be a reliable and accurate programme we can offer no guarantees at all as to any aspect of its running/accuracy/reliability/... (i.e. remember what you paid for it).

If you want to use this programme then first read the instructions here. Then you need to downlad the two files: the programme itself and a graphics driver. These two files need to be in the same directory that you use to run the programme. To run the programme, you need to open a DOS window and navigate to the same directory containing the POWER.EXE (as explained in the instructions).

Step 0: Users of Windows Vista and Mac and Linux (and others experiencing problems with earlier versions of Windows) may need to download and install a DOS emulator such as DOSbox. Instructions on this are given in the section Operation under Windows Vista (etc) here.

Step 1: Download Graphics Driver

Step 2: Download POWER.EXE

Step 3: Use Windows explorer to check that names of files are Egavga.bgi and power.exe and change their names if necessary to these using Explorer (see instructions).

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This page is maintained by the Dr Nick Fieller and was last updated on 12 November 2007.