```Date: Wed, 2 Aug 2006 19:25:47 +0200 Reply-To: Marta García-Granero Sender: "SPSSX(r) Discussion" From: Marta García-Granero Organization: Asesoría Bioestadística Subject: Re: the accuracy of the device In-Reply-To: <20060802162856.34568.qmail@web38212.mail.mud.yahoo.com> Content-Type: text/plain; charset=ISO-8859-1 Hi Omar OF> My colleague would like to examine accuracy or the OF> reliability of a device , the device measuring teeth's strength. OF> He has 50 teeth , he will measure the teeth’s strength OF> today and after 2 or 3 days he will do the same process by using OF> the same device , to examine the accuracy of the device. Could OF> we use Paired-Samples T Test if the data follow the normal OF> distribution or we should use Two-Related-Samples Tests if the OF> data non normal? Neither test you mention will answer your question (measurement error), since both focus on whether there is a bias (systematic difference between the two days). I suppose you want statistics to verify the repeatability of a device (the ammount of random variation). A p-value (obtained by any test) will not answer the question. Take a look at these links: http://bmj.bmjjournals.com/cgi/content/full/313/7059/744 http://bmj.bmjjournals.com/cgi/content/full/313/7048/41 http://www-users.york.ac.uk/~mb55/meas/ Time ago I wrote some code for the methods discussed in those appers. Let me know if you are interested in having it. -- Regards, Dr. Marta García-Granero,PhD mailto:biostatistics@terra.es Statistician --- "It is unwise to use a statistical procedure whose use one does not understand. SPSS syntax guide cannot supply this knowledge, and it is certainly no substitute for the basic understanding of statistics and statistical thinking that is essential for the wise choice of methods and the correct interpretation of their results". (Adapted from WinPepi manual - I'm sure Joe Abrahmson will not mind) ```

Back to: Top of message | Previous page | Main SPSSX-L page