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I just noticed all the discussion about how you NEVER should compute the
mean of an ordinal variable. While I can't disagree with many of the fine alternatives being suggested, I would mention that it is dangerous to say "never". Most people (including many statisticians) use a statistic called grade point average (GPA) in their hiring decisions. This is clearly an average computed on ordinal (A, B, C, D, F) data. Is it an awful thing to pretend that these numbers can be averaged? Well it implies that two C's are equivalent to an A and an F. Still, the GPA doesn't do too much violence to the data, and I think all of us would agree that a 3.5 GPA is better than a 2.5 GPA. Whether you should average or not depends a lot on the distribution of the ordinal categories, the number of levels of the ordinal variable, what the levels of the ordinal variable represent, and what the goals of the statistical summary are. I'd argue that the average of a 6 point variable is a simple summary that is useful for descriptive statistics or informal comparisons. I'd save the more complex alternatives for larger projects where a "quick and dirty" approximation would be inappropriate. I talk a bit more about this and point out the problems with a commonly used alternative for ordinal data, rank-based methods, at my old website: * http://www.childrensmercy.org/stats/weblog2005/OrdinalData.asp -- Steve Simon, Standard Disclaimer Sign up for The Monthly Mean, the newsletter that dares to call itself "average" at www.pmean.com/news "Data entry and data management issues with examples in IBM SPSS," Tuesday, August 24, 11am-noon CDT. Free webinar. Details at www.pmean.com/webinars ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD |
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Administrator
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Nice note on your website, Steve. I have two comments.
1. I believe that Likert would only have used the term "scale" after summing or averaging over several items. I.e., it takes more than one Likert-type item to make a scale. 2. If I'm not mistaken, Likert tried several more complex methods of assigning numbers to the ordinal categories (like your -3 -1 0 1 3 example), and concluded that none of them improved substantially on just assigning consecutive integers. Cheers, Bruce
--
Bruce Weaver bweaver@lakeheadu.ca http://sites.google.com/a/lakeheadu.ca/bweaver/ "When all else fails, RTFM." PLEASE NOTE THE FOLLOWING: 1. My Hotmail account is not monitored regularly. To send me an e-mail, please use the address shown above. 2. The SPSSX Discussion forum on Nabble is no longer linked to the SPSSX-L listserv administered by UGA (https://listserv.uga.edu/). |
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In reply to this post by Steve Simon, P.Mean Consulting
It still a BAD idea, I am much more interested in the number of As/Number of courses taken than the mean GPA I would certainly take someone with 2As, and 4Cs, gp = 16/6 = 2.67 or even 2As , 3 Cs and a D, gpa = 2.5, over someone with 6 Bs gpa =3 Using gpa encourages mediocrity over focussed excellence, and in my view feeds into passion and interest in knowledge in a very undesirable way. The student with passionate interest in some topic has to sacrifice that passion to make sure of Bs in topics of peripheral interest. Is that good? I do not recommend ranks which loses even more information than means. I recommend proprotion or cumulative proportions whihch is more nearly aligned with what the decision maker needs to know. This is equally true of applied problems such as customer satisfaction. One needs to know how many people hate as well as how many people like. Averaging ordinal items lets the bad news get hidden in the average, as above a respectable average may be obtained while both the good and the bad news gets hidden. If I am told that programme X has higher gpa than programme Y, I am unumpressed. I want to KNOW whether that is due to improvement of proportion of good or of weaker grades. For all we know there was a shift form p(d) > p ( c) associated with a slightly smaller shift form p(a) to p(b). Happy about that? Its our job as folk with statistics knpwledge to discourage these practice, and if we cannot avoid giving the means, at lieast ensure that more appropriate (proportion measures) are also available, i.e calculateable from information provided End of rant..... Best diana On 09/08/2010 15:26, "Steve Simon, P.Mean Consulting" <net@...> wrote: I just noticed all the discussion about how you NEVER should compute the Professor Diana Kornbrot email: d.e.kornbrot@... web: http://web.me.com/kornbrot/KornbrotHome.html Work Centre for Lifespan & Chronic Illness Research, CLiCIR School of Psychology University of Hertfordshire College Lane, Hatfield, Hertfordshire AL10 9AB, UK voice: +44 (0) 170 728 4626 Home 19 Elmhurst Avenue London N2 0LT, UK voice: +44 (0) 208 883 3657 mobile: +44 (0) 7855 415 425 fax: +44 (0) 870 706 4997 |
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Re: 6 point variable
Why don't you just group the top two and bottom two, express them as % and then subtract the bottom two from the top two and express that as % diff? Most clients can understand that. There are only two answers to any question, "Yes" and "No", so my mates say, but at a pinch you can split these with "Is that a little or a lot?" which gives you a compromise of four points. John Hall http://surveyresearch.weebly.com ----- Original Message ----- From: Kornbrot, Diana To: [hidden email] Sent: Monday, August 09, 2010 5:25 PM Subject: Re: 6 point variable Of course, averaging ordinal data is VERY common It still a BAD idea, I am much more interested in the number of As/Number of courses taken than the mean GPA I would certainly take someone with 2As, and 4Cs, gp = 16/6 = 2.67 or even 2As , 3 Cs and a D, gpa = 2.5, over someone with 6 Bs gpa =3 Using gpa encourages mediocrity over focussed excellence, and in my view feeds into passion and interest in knowledge in a very undesirable way. The student with passionate interest in some topic has to sacrifice that passion to make sure of Bs in topics of peripheral interest. Is that good? I do not recommend ranks which loses even more information than means. I recommend proprotion or cumulative proportions whihch is more nearly aligned with what the decision maker needs to know. This is equally true of applied problems such as customer satisfaction. One needs to know how many people hate as well as how many people like. Averaging ordinal items lets the bad news get hidden in the average, as above a respectable average may be obtained while both the good and the bad news gets hidden. If I am told that programme X has higher gpa than programme Y, I am unumpressed. I want to KNOW whether that is due to improvement of proportion of good or of weaker grades. For all we know there was a shift form p(d) > p ( c) associated with a slightly smaller shift form p(a) to p(b). Happy about that? Its our job as folk with statistics knpwledge to discourage these practice, and if we cannot avoid giving the means, at lieast ensure that more appropriate (proportion measures) are also available, i.e calculateable from information provided End of rant..... Best diana On 09/08/2010 15:26, "Steve Simon, P.Mean Consulting" <[hidden email]> wrote: I just noticed all the discussion about how you NEVER should compute the mean of an ordinal variable. While I can't disagree with many of the fine alternatives being suggested, I would mention that it is dangerous to say "never". Most people (including many statisticians) use a statistic called grade point average (GPA) in their hiring decisions. This is clearly an average computed on ordinal (A, B, C, D, F) data. Is it an awful thing to pretend that these numbers can be averaged? Well it implies that two C's are equivalent to an A and an F. Still, the GPA doesn't do too much violence to the data, and I think all of us would agree that a 3.5 GPA is better than a 2.5 GPA. Whether you should average or not depends a lot on the distribution of the ordinal categories, the number of levels of the ordinal variable, what the levels of the ordinal variable represent, and what the goals of the statistical summary are. I'd argue that the average of a 6 point variable is a simple summary that is useful for descriptive statistics or informal comparisons. I'd save the more complex alternatives for larger projects where a "quick and dirty" approximation would be inappropriate. I talk a bit more about this and point out the problems with a commonly used alternative for ordinal data, rank-based methods, at my old website: * http://www.childrensmercy.org/stats/weblog2005/OrdinalData.asp -- Steve Simon, Standard Disclaimer Sign up for The Monthly Mean, the newsletter that dares to call itself "average" at www.pmean.com/news "Data entry and data management issues with examples in IBM SPSS," Tuesday, August 24, 11am-noon CDT. Free webinar. Details at www.pmean.com/webinars ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD Professor Diana Kornbrot email: [hidden email] web: http://web.me.com/kornbrot/KornbrotHome.html Work Centre for Lifespan & Chronic Illness Research, CLiCIR School of Psychology University of Hertfordshire College Lane, Hatfield, Hertfordshire AL10 9AB, UK voice: +44 (0) 170 728 4626 Home 19 Elmhurst Avenue London N2 0LT, UK voice: +44 (0) 208 883 3657 mobile: +44 (0) 7855 415 425 fax: +44 (0) 870 706 4997 ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD |
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Hi!
So, John, 20% "Yes" and 20% "No" = 0% difference; and 45% "Yes" and 45% "No" = 0% difference. But in your analysis they are treated the same? If that is the case I don't agree. My recommendation is to keep information "simple" and do not forget that the distribution is at least as interesting as the average. All the best Wilhelm (Wille) Landerholm +46-735-460000 Queue/STATB Making sense of data BOX 92 | 162 12 Vallingby | Sweden 2010/8/10 John F Hall <[hidden email]> Re: 6 point variable |
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In reply to this post by Jarrod Teo-2
The scales of course sum ordinal variables. As Bruce, states, Likert did look empirically at consequences of summing ordinal items. I believe he argues that if there are a ‘reasonable’ number of items then results based on scales are fairly robust, due to the central limit theorem, cf Dawes, R. M. (1979). The robust beauty of improper linear models American Psychologist , Vol. 34, pp. 571-582. (1610 citations!) Still think NEVER is appropriate if extreme, for Likert ITEMS Best Diana
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In reply to this post by Marta Garcia-Granero
At 02:04 PM 8/2/2010, Marta García-Granero wrote:
>C'mon, "us.ibm.com" people, say something... >could we have SPSS 15 as a cheap home version? >could we, could we, could we? pleeeease? That is an interesting thought, which has also occurred to me: The cheapest and easiest cut-down version SPSS could offer, would be the regular system, several releases back. Some organizations effectively do something like this, by buying only every few releases. I think it'd have to be at least 4 releases back, or too many full-pay commercial customers would say 'what the heck', and get the cheap one. With SPSS selling permanent licenses, as it does (though not only those), users can move out of SPSS with 'graceful degradation' of their capabilities. That is, by simply staying with the last version they have, users can migrate code and files at whatever pace suits them -- their SPSS will get less and less capable compared with current versions, but won't disappear. (By contrast, SAS's annual-license policy locks you into their high annual fee essentially forever: let a renewal go by, and EVERYTHING stops working. Users who migrate must migrate everything within one year, or else. That's one reason small users almost never consider SAS. And, SAS users: save EVERY file you care about, in portable format, and make sure it can be read by something besides SAS.) ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD |
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Hi Richard:
Richard Ristow wrote: > > That is an interesting thought, which has also occurred to me: > > The cheapest and easiest cut-down version SPSS could offer, would be > the regular system, several releases back. Some organizations > effectively do something like this, by buying only every few releases. > > I think it'd have to be at least 4 releases back, or too many full-pay > commercial customers would say 'what the heck', and get the cheap one. In my opinion, that cut-down version of SPSS should be available only for academic institutions, like Universities, to keep "full-pay commercial customers" from benefiting of the cheap version. Thus, in the short run, SPSS-IBM would get some money from customers they are going to lose very soon (like my University), and, in the long run, SPSS would still be known to graduated people, future employees of those companies that would go on using the full version, instead of switching to another one. I hope someone up the chain of command in SPSS-IBM will get to read all the exchange we've had concerning SPSS 15. Best regards, Marta GG -- For miscellaneous SPSS related statistical stuff, visit: http://gjyp.nl/marta/ ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD |
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> In my opinion, that cut-down version of SPSS should be available only
> for academic institutions, like Universities, to keep "full-pay > commercial customers" from benefiting of the cheap version. Thus, in the > short run, SPSS-IBM would get some money from customers they are going > to lose very soon (like my University), and, in the long run, SPSS would > still be known to graduated people, future employees of those companies > that would go on using the full version, instead of switching to another > one. It's not only the academic world that's annoyed with the SPSS licensing terms. My company had plans changing to Stata, but SPSS did us a better offer at last. When testing Stata, one of my main disadvantages was that importing and exporting data to other programs (like excel/access) is far more difficult then with SPSS. And we do that very often. You need some sort of converting program. Francien ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD |
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I always found outsheet/outfile and insheet in Stata to be fairly
powerful and relatively simple. (Of course, StatTransfer is way easier.) Cheers, Nils On Wed, Aug 18, 2010 at 7:05 AM, Francien Berndsen <[hidden email]> wrote: >> In my opinion, that cut-down version of SPSS should be available only >> for academic institutions, like Universities, to keep "full-pay >> commercial customers" from benefiting of the cheap version. Thus, in the >> short run, SPSS-IBM would get some money from customers they are going >> to lose very soon (like my University), and, in the long run, SPSS would >> still be known to graduated people, future employees of those companies >> that would go on using the full version, instead of switching to another >> one. > > It's not only the academic world that's annoyed with the SPSS licensing > terms. My company had plans changing to Stata, but SPSS did us a better > offer at last. > > When testing Stata, one of my main disadvantages was that importing and > exporting data to other programs (like excel/access) is far more difficult > then with SPSS. And we do that very often. You need some sort of converting > program. > > Francien > > ===================== > To manage your subscription to SPSSX-L, send a message to > [hidden email] (not to SPSSX-L), with no body text except the > command. To leave the list, send the command > SIGNOFF SPSSX-L > For a list of commands to manage subscriptions, send the command > INFO REFCARD > ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD |
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In reply to this post by Francien Berndsen
StatTransfer software does an exellent job of converting all types of databases:
http://www.stattransfer.com/ I have no financial interest in this software. ~~~~~~~~~~~ Scott R Millis, PhD, ABPP, CStat, CSci Professor & Director of Research Dept of Physical Medicine & Rehabilitation Dept of Emergency Medicine Wayne State University School of Medicine 261 Mack Blvd Detroit, MI 48201 Email: [hidden email] Email: [hidden email] Tel: 313-993-8085 Fax: 313-966-7682 --- On Wed, 8/18/10, Francien Berndsen <[hidden email]> wrote: > From: Francien Berndsen <[hidden email]> > Subject: Re: inexpensive 'home' version? > To: [hidden email] > Date: Wednesday, August 18, 2010, 2:05 AM > > In my opinion, that cut-down > version of SPSS should be available only > > for academic institutions, like Universities, to keep > "full-pay > > commercial customers" from benefiting of the cheap > version. Thus, in the > > short run, SPSS-IBM would get some money from > customers they are going > > to lose very soon (like my University), and, in the > long run, SPSS would > > still be known to graduated people, future employees > of those companies > > that would go on using the full version, instead of > switching to another > > one. > > It's not only the academic world that's annoyed with the > SPSS licensing > terms. My company had plans changing to Stata, but SPSS did > us a better > offer at last. > > When testing Stata, one of my main disadvantages was that > importing and > exporting data to other programs (like excel/access) is far > more difficult > then with SPSS. And we do that very often. You need some > sort of converting > program. > > Francien > > ===================== > To manage your subscription to SPSSX-L, send a message to > [hidden email] > (not to SPSSX-L), with no body text except the > command. To leave the list, send the command > SIGNOFF SPSSX-L > For a list of commands to manage subscriptions, send the > command > INFO REFCARD > ===================== To manage your subscription to SPSSX-L, send a message to [hidden email] (not to SPSSX-L), with no body text except the command. To leave the list, send the command SIGNOFF SPSSX-L For a list of commands to manage subscriptions, send the command INFO REFCARD |
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