Date: Sun, 4 Feb 2007 09:02:33 +0330
ReplyTo: Siavoush Dastmalchi <dastmalchi.s@tbzmed.ac.ir>
Sender: "SPSSX(r) Discussion" <SPSSXL@LISTSERV.UGA.EDU>
From: Siavoush Dastmalchi <dastmalchi.s@tbzmed.ac.ir>
Subject: suitable statistical tests
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Dear all,
I will appreciate it if you could kindly suggest me a suitable statistical test for the following problem. I have used two tests, but need to know if they are okay.
Suppose I am testing three different methods to predict an structural property for integral membrane proteins called alpha angle (which determines the rotational orientation of the alpha helical transmembrane segment of membrane). I have selected several protein with total of 125 alpha helices. I have measured the alpha angles (125 angles) and then predicted them using three different methods. Then I have performed two different test to compare the performances of three prediction methods:
1. The measured alpha angles were compared with the predicted values and the mean differences are calculated for three methods. Then the mean differences were compared with each other using twotailed paired ttest.
2. the second way of comparing the prediction methods was as following:
A criterion was set to judge on the performance of a method. For example if a predicted alpha angle was in the range of +/ 20 degree from the measured experimental value, it is considered a correct prediction. Then the number (% or ration) of correct predictions for three different prediction methods were determined. For example method A in 50% of 125 cases predicted the alpha angle with absolute deviation less than 20 degree, method B in 40% of cases and method C in 65% of cases. Then the performances of prediction methods were compared using the statistical test for comparing difference in proportions (comparing P1 and P2).
Cheers, Siavoush
