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Date:         Sun, 4 Feb 2007 09:02:33 +0330
Reply-To:     Siavoush Dastmalchi <>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Siavoush Dastmalchi <>
Subject:      suitable statistical tests
Content-Type: text/plain; charset="iso-8859-1"

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 two-tailed paired t-test.

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

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