Date: Wed, 2 Aug 2006 19:25:47 +0200
Reply-To: Marta García-Granero
<biostatistics@terra.es>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Marta García-Granero
<biostatistics@terra.es>
Organization: Asesoría Bioestadística
Subject: Re: the accuracy of the device
In-Reply-To: <20060802162856.34568.qmail@web38212.mail.mud.yahoo.com>
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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)
