Hello listers,
I am trying to discern group differences. I am looking for a dichotomous categorical independent-by-ordinal dependent test, when the ordinal variable has a small number of categories (3-5) and/or some cells have small counts. In a previous post to this list (Mar. 15, 2006) a Mantel- Haenszel chi-square was identified as taking into account ordinality of the second variable. Can SPSS compute a Mantel-Haenszel chi-square for a rectangular table? The option available with crosstabs appears to be suited to 2x2 tables only (odds ratio). Am I correct in eliminating Mann-Whitney U because apparently it is not reliable unless the ordinal variable has a high number of categories and similar distribution properties. If there is a suitable test to consider, pls advise. Thanks so much for your consideration of this request. Glenys Lafrance |
Hi Glenys
GL> I am trying to discern group differences. I am looking for a dichotomous GL> categorical independent-by-ordinal dependent test, when the ordinal GL> variable has a small number of categories (3-5) and/or some cells have GL> small counts. In a previous post to this list (Mar. 15, 2006) a Mantel- GL> Haenszel chi-square was identified as taking into account ordinality of the GL> second variable. Can SPSS compute a Mantel-Haenszel chi-square for a GL> rectangular table? Yes. It's part of the standard CROSSTABS output when you ask for Chi-square statistics. It's called "Linear-by-linear association". If you have small cell counts (observed or expected? it's not the same), you had better ask for a exact p-value (provided you have the EXACT TESTS module installed). You can also use the Cochran-Armitage test for trend in this situation (can be programmed with SPSS - I did it - but without the exact p-value, only asymptotic significance) GL> The option available with crosstabs appears to be GL> suited to 2x2 tables only (odds ratio). You are mixing things a bit: this statistics you are talking about is the weighed average of 2 or more stratum-OR when you are performing stratified analysis. It has nothing to do with the situation we are discussing now (trends). GL> Am I correct in eliminating Mann-Whitney U because apparently it is not GL> reliable unless the ordinal variable has a high number of categories and GL> similar distribution properties. Yes -- Regards, Dr. Marta García-Granero,PhD mailto:[hidden email] 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) |
Dear Marta
I found your reply very interesting. Are you also able to advise why on occasions SPSS output for the Mantel-Haenszel chi-square test should include a footnote to the corresponding test statistic value which quotes a standardized value which is completely different from the tabulated one (please see my message of 17 October 2006). Many thanks Best wishes Margaret Marta García-Granero <[hidden email]> wrote: Hi Glenys GL> I am trying to discern group differences. I am looking for a dichotomous GL> categorical independent-by-ordinal dependent test, when the ordinal GL> variable has a small number of categories (3-5) and/or some cells have GL> small counts. In a previous post to this list (Mar. 15, 2006) a Mantel- GL> Haenszel chi-square was identified as taking into account ordinality of the GL> second variable. Can SPSS compute a Mantel-Haenszel chi-square for a GL> rectangular table? Yes. It's part of the standard CROSSTABS output when you ask for Chi-square statistics. It's called "Linear-by-linear association". If you have small cell counts (observed or expected? it's not the same), you had better ask for a exact p-value (provided you have the EXACT TESTS module installed). You can also use the Cochran-Armitage test for trend in this situation (can be programmed with SPSS - I did it - but without the exact p-value, only asymptotic significance) GL> The option available with crosstabs appears to be GL> suited to 2x2 tables only (odds ratio). You are mixing things a bit: this statistics you are talking about is the weighed average of 2 or more stratum-OR when you are performing stratified analysis. It has nothing to do with the situation we are discussing now (trends). GL> Am I correct in eliminating Mann-Whitney U because apparently it is not GL> reliable unless the ordinal variable has a high number of categories and GL> similar distribution properties. Yes -- Regards, Dr. Marta García-Granero,PhD mailto:[hidden email] 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) Send instant messages to your online friends http://uk.messenger.yahoo.com |
The linear-by-linear chi-square has 1 degree of freedom.
The standardized value looks like the square root of the linear-by-linear chi-square. Recall that the chi-square for 1 degree of freedom is a "z-square," where z is standard normal. -----Original Message----- From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Margaret MacDougall Sent: Wednesday, October 18, 2006 11:23 AM To: [hidden email] Subject: Re: Mantel-Haenszel Chi-Square or Alternative Test Dear Marta I found your reply very interesting. Are you also able to advise why on occasions SPSS output for the Mantel-Haenszel chi-square test should include a footnote to the corresponding test statistic value which quotes a standardized value which is completely different from the tabulated one (please see my message of 17 October 2006). Many thanks Best wishes Margaret Marta García-Granero <[hidden email]> wrote: Hi Glenys GL> I am trying to discern group differences. I am looking for a dichotomous GL> categorical independent-by-ordinal dependent test, when the ordinal GL> variable has a small number of categories (3-5) and/or some cells have GL> small counts. In a previous post to this list (Mar. 15, 2006) a Mantel- GL> Haenszel chi-square was identified as taking into account ordinality of the GL> second variable. Can SPSS compute a Mantel-Haenszel chi-square for a GL> rectangular table? Yes. It's part of the standard CROSSTABS output when you ask for Chi-square statistics. It's called "Linear-by-linear association". If you have small cell counts (observed or expected? it's not the same), you had better ask for a exact p-value (provided you have the EXACT TESTS module installed). You can also use the Cochran-Armitage test for trend in this situation (can be programmed with SPSS - I did it - but without the exact p-value, only asymptotic significance) GL> The option available with crosstabs appears to be GL> suited to 2x2 tables only (odds ratio). You are mixing things a bit: this statistics you are talking about is the weighed average of 2 or more stratum-OR when you are performing stratified analysis. It has nothing to do with the situation we are discussing now (trends). GL> Am I correct in eliminating Mann-Whitney U because apparently it is not GL> reliable unless the ordinal variable has a high number of categories and GL> similar distribution properties. Yes -- Regards, Dr. Marta García-Granero,PhD mailto:[hidden email] 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) Send instant messages to your online friends http://uk.messenger.yahoo.com |
Dear Anthony
Thank you. What you are saying is very clear. Best wishes Margaret Anthony Babinec <[hidden email]> wrote: The linear-by-linear chi-square has 1 degree of freedom. The standardized value looks like the square root of the linear-by-linear chi-square. Recall that the chi-square for 1 degree of freedom is a "z-square," where z is standard normal. -----Original Message----- From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Margaret MacDougall Sent: Wednesday, October 18, 2006 11:23 AM To: [hidden email] Subject: Re: Mantel-Haenszel Chi-Square or Alternative Test Dear Marta I found your reply very interesting. Are you also able to advise why on occasions SPSS output for the Mantel-Haenszel chi-square test should include a footnote to the corresponding test statistic value which quotes a standardized value which is completely different from the tabulated one (please see my message of 17 October 2006). Many thanks Best wishes Margaret Marta García-Granero wrote: Hi Glenys GL> I am trying to discern group differences. I am looking for a dichotomous GL> categorical independent-by-ordinal dependent test, when the ordinal GL> variable has a small number of categories (3-5) and/or some cells have GL> small counts. In a previous post to this list (Mar. 15, 2006) a Mantel- GL> Haenszel chi-square was identified as taking into account ordinality of the GL> second variable. Can SPSS compute a Mantel-Haenszel chi-square for a GL> rectangular table? Yes. It's part of the standard CROSSTABS output when you ask for Chi-square statistics. It's called "Linear-by-linear association". If you have small cell counts (observed or expected? it's not the same), you had better ask for a exact p-value (provided you have the EXACT TESTS module installed). You can also use the Cochran-Armitage test for trend in this situation (can be programmed with SPSS - I did it - but without the exact p-value, only asymptotic significance) GL> The option available with crosstabs appears to be GL> suited to 2x2 tables only (odds ratio). You are mixing things a bit: this statistics you are talking about is the weighed average of 2 or more stratum-OR when you are performing stratified analysis. It has nothing to do with the situation we are discussing now (trends). GL> Am I correct in eliminating Mann-Whitney U because apparently it is not GL> reliable unless the ordinal variable has a high number of categories and GL> similar distribution properties. Yes -- Regards, Dr. Marta García-Granero,PhD mailto:[hidden email] 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) Send instant messages to your online friends http://uk.messenger.yahoo.com Send instant messages to your online friends http://uk.messenger.yahoo.com |
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