Re: Is there a way, either within SPSS or outside of it, to conduct nonparametric tests while preserving fractional weights?

Posted by Art Kendall on Jan 20, 2012; 12:37pm
URL: http://spssx-discussion.165.s1.nabble.com/Is-there-a-way-either-within-SPSS-or-outside-of-it-to-conduct-nonparametric-tests-while-preserving-f-tp5159185p5160297.html

Please explain your study in more detail.

Why are you considering nonparametric approaches?

Is an "event" a case"?  How were they selected?
Please describe your variables,  meaning, level of measurement, value labels, role (IV, DV, something to control), etc.
Are there repeated measures within an event?


On 1/19/2012 5:32 PM, Martha Hewett wrote:

According to the PASW 18 help files, the NPAR tests round weights to the nearest integer.  But the RANK function uses the sum of the case weights, even if they are not integers (I have tested this and found that it used the fractional weight, not a rounded weight).  

Here is my problem:  I have particle events in two different types of environments.  Each event is characterized by two features.  One is its light-absorbing properties for a couple of particular wavelengths (theta), and the other is its size.  I have conducted nonparametric tests of the distribution of events in each environment by theta, and they are different.  That's interesting, but the size of events as a function of theta is also different for the two environments, and both the size and the theta need to be taken into account in looking at difference in people's exposure.  So, I would like to conduct some kind of nonparametric test to compare the distribution of the total mass of events as a function of theta for the two environments.  So I would like to weight by mass (size) and then conduct Kolmogorov-Smirnov tests and perhaps  Mann-Whitney U tests.  The distribution of events by size is probably more or less logarithmic, but the distribution by theta is not any kind of smooth function, so parametric tests are not an option.  

Is there a theoretical reason why you could compute a K-S test or MW-U with integer weights but not non-integer weights?  If not, is there another tool that can do it if SPSS cannot?  (I do have Stata but haven't used it much yet).   Is there a better test for what I'm trying to do?  

Martha Hewett  |

Director of Research | 612.335.5865

Center for Energy and Environment

212 Third Avenue North, Suite 560 | Minneapolis, MN 55401

(cell) 612.839.2358 | (fax) 612.335.5888 | www.mncee.org

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