interpreting t-test results
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I have set of results for two different tests taken by the same subjects. I
am using the paired sample t-test in SPSS, I assume that is the right one. I get a significant difference between the two test, both are psychological measures, but I would like to know which test gives me the higher score i.e which psychological construct is most prevalent in my sample, the test scores are calculated differently one ranges from 1- 4 and the other from 24-120. Would I use another analysis to get this answer? ===================== 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 |
Re: interpreting t-test results
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At 07:57 PM 4/5/2009, Talino Bruno wrote:
>I have set of results for two different tests taken by the same >subjects. I am using the paired sample t-test in SPSS, I assume that >is the right one. I get a significant difference between the >two test, both are psychological measures, but I would like to know >which test gives me the higher score i.e which psychological >construct is most prevalent in my sample, the test scores are >calculated differently one ranges from 1- 4 and the other from >24-120. Would I use another analysis to get this answer? The paired t-test tells you whether the score consistently increases or decreases from the first test to the second. If the scores on the first test are 4 or less, and those on the second are 24 or more, then the numerical change from the first to the second is always positive. The t-test will show a clearly significant result, but that's an artifact; it's meaningless. You can't test for a significant difference, or even define what it is, unless the two quantities are measured on the same scale. ===================== 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 |
Re: interpreting t-test results
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In reply to this post by Talino Bruno
Talino,
You would need to compare scales that are based on the same metric in order to have a meaningful result. The numbers for the second scale may be higher because the rating scale uses larger numbers, but that does not imply that levels of some construct are higher. HTH, Steve Brand www.StatisticsDoc.com -----Original Message----- From: SPSSX(r) Discussion [mailto:[hidden email]]On Behalf Of Talino Bruno Sent: Sunday, April 05, 2009 7:58 PM To: [hidden email] Subject: interpreting t-test results I have set of results for two different tests taken by the same subjects. I am using the paired sample t-test in SPSS, I assume that is the right one. I get a significant difference between the two test, both are psychological measures, but I would like to know which test gives me the higher score i.e which psychological construct is most prevalent in my sample, the test scores are calculated differently one ranges from 1- 4 and the other from 24-120. Would I use another analysis to get this answer? ===================== 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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So the question is if it's only the coding which is different or if
it's two completely different measures. Can you, in other words, recode one scale into the other before the t-test? Best, Henrik Quoting Statisticsdoc <[hidden email]>: > Talino, > > You would need to compare scales that are based on the same metric in order > to have a meaningful result. The numbers for the second scale may be higher > because the rating scale uses larger numbers, but that does not imply that > levels of some construct are higher. > > HTH, > > Steve Brand > > www.StatisticsDoc.com > > -----Original Message----- > From: SPSSX(r) Discussion [mailto:[hidden email]]On Behalf Of > Talino Bruno > Sent: Sunday, April 05, 2009 7:58 PM > To: [hidden email] > Subject: interpreting t-test results > > > I have set of results for two different tests taken by the same subjects. I > am using the paired sample t-test in SPSS, I assume that is the right one. > I get a significant difference between the two test, both are > psychological measures, but I would like to know which test gives me the > higher score i.e which psychological construct is most prevalent in my > sample, the test scores are calculated differently one ranges from 1- 4 and > the other from 24-120. Would I use another analysis to get this answer? > > ===================== > 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 > ************************************************************ Henrik Lolle Department of Economics, Politics and Public Administration Aalborg University Fibigerstraede 1 9200 Aalborg Phone: (+45) 99 40 81 84 ************************************************************ ===================== 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 Talino Bruno
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Re: interpreting t-test results
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In reply to this post by Talino Bruno
Hi Talino,
Given that one scale measures only from 1-4, is that a measure of the construct you're interested in, alone ? The other test ranges from 24-120...much bigger...but is it possible to do a similar thing and extract the one question that measures the construct you're interested in, albeit from a different angle ? You might then be able to compare the two tests on that one construct.....although they might still be based on a different metric (the objection raised so far)....isn't this part of what you are after ? But it may be too simple to think that you can extract the question that draws on your construct of interest like this. Just a thought, Martin ----- Original Message ----- From: "Talino Bruno" <[hidden email]> To: <[hidden email]> Sent: Monday, April 06, 2009 12:57 AM Subject: interpreting t-test results >I have set of results for two different tests taken by the same subjects. I > am using the paired sample t-test in SPSS, I assume that is the right one. > I get a significant difference between the two test, both are > psychological measures, but I would like to know which test gives me the > higher score i.e which psychological construct is most prevalent in my > sample, the test scores are calculated differently one ranges from 1- 4 > and > the other from 24-120. Would I use another analysis to get this answer? > > ===================== > 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 |
Re: interpreting t-test results
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In reply to this post by Jims More
is this not what z scores are for?
or am I missing something M From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Jims More Sent: 06 April 2009 09:56 To: [hidden email] Subject: Re: interpreting t-test results
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Re: interpreting t-test results
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In reply to this post by Talino Bruno
After reading some of the other responses, i.e., re-centering the scores so
they have a common mean and standard deviation, and picking an item indicative of the "construct of interest", I think finding a third, and maybe a forth, test that you know tests the "constructs of interest" then correlating the scores from the first two test with the new tests. That should give a more precise indication of which construct in more higher/stronger in the first two. Arthur Kramer "...believe half of what you see and none of what you hear." N.Whitfield and B.Strong -----Original Message----- From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Talino Bruno Sent: Sunday, April 05, 2009 7:58 PM To: [hidden email] Subject: interpreting t-test results I have set of results for two different tests taken by the same subjects. I am using the paired sample t-test in SPSS, I assume that is the right one. I get a significant difference between the two test, both are psychological measures, but I would like to know which test gives me the higher score i.e which psychological construct is most prevalent in my sample, the test scores are calculated differently one ranges from 1- 4 and the other from 24-120. Would I use another analysis to get this answer? ===================== 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 |
Re: interpreting t-test results
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In reply to this post by Martin P. Holt-2
Hi Talino,
What you are trying to do is compare apples and oranges or elephants and ants to see if they are different. You can only compare the results of two psychometric tests if they are on the same metric. A major requirement for putting tests on the same metric would be that broadly measure the same construct. If they do, then you can recalibrate the items to produce a common scale and then compare your results. Many programmes are available to do this, but I suggest something like Bilog MG. Cheers, Darren -----Original Message----- From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Martin Holt Sent: 06 April 2009 10:42 To: [hidden email] Subject: Re: interpreting t-test results Hi Talino, Given that one scale measures only from 1-4, is that a measure of the construct you're interested in, alone ? The other test ranges from 24-120...much bigger...but is it possible to do a similar thing and extract the one question that measures the construct you're interested in, albeit from a different angle ? You might then be able to compare the two tests on that one construct.....although they might still be based on a different metric (the objection raised so far)....isn't this part of what you are after ? But it may be too simple to think that you can extract the question that draws on your construct of interest like this. Just a thought, Martin ----- Original Message ----- From: "Talino Bruno" <[hidden email]> To: <[hidden email]> Sent: Monday, April 06, 2009 12:57 AM Subject: interpreting t-test results >I have set of results for two different tests taken by the same subjects. I > am using the paired sample t-test in SPSS, I assume that is the right one. > I get a significant difference between the two test, both are > psychological measures, but I would like to know which test gives me the > higher score i.e which psychological construct is most prevalent in my > sample, the test scores are calculated differently one ranges from 1- 4 > and > the other from 24-120. Would I use another analysis to get this answer? > > ===================== > 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 _____________________________________________________________________ This e-mail has been scanned for viruses by Verizon Business Internet Managed Scanning Services - powered by MessageLabs. For further information visit http://www.verizonbusiness.com/uk No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.0.238 / Virus Database: 270.11.42/2042 - Release Date: 04/05/09 10:54:00 _____________________________________________________________________ This e-mail has been scanned for viruses by Verizon Business Internet Managed Scanning Services - powered by MessageLabs. For further information visit http://www.verizonbusiness.com/uk ===================== 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 Arthur Kramer
Apologies if I've missed aome of the previous replies, but my 2cents worth -
Let's suppose your two psychological contstructs are extraversion and neuroticism. You say you want to find which of the two is "more prevalent in your sample". The only ay I can make sense of this is to think in terms of norm comparisons. You want to find whether your sample is significantly different from some reference population on either or both of the constructs. A t-test - any paired sample approcah - is no good here as some contributors have already pointed out. You need to compare your sample scores with the scores of some normative reference popuation. If for example you find the sample mean for extraversion is not significantly different from the mean of the reference population norm, but the neuroticism mean does differ from that in the reference population, you could conclude that neuroticism was 'more prevalent' in your sample (than in the norm population), but extraversion was not. Garry Gelade Business Analytic Ltd -----Original Message----- From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Arthur Kramer Sent: 06 April 2009 14:46 To: [hidden email] Subject: Re: interpreting t-test results After reading some of the other responses, i.e., re-centering the scores so they have a common mean and standard deviation, and picking an item indicative of the "construct of interest", I think finding a third, and maybe a forth, test that you know tests the "constructs of interest" then correlating the scores from the first two test with the new tests. That should give a more precise indication of which construct in more higher/stronger in the first two. Arthur Kramer "...believe half of what you see and none of what you hear." N.Whitfield and B.Strong -----Original Message----- From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Talino Bruno Sent: Sunday, April 05, 2009 7:58 PM To: [hidden email] Subject: interpreting t-test results I have set of results for two different tests taken by the same subjects. I am using the paired sample t-test in SPSS, I assume that is the right one. I get a significant difference between the two test, both are psychological measures, but I would like to know which test gives me the higher score i.e which psychological construct is most prevalent in my sample, the test scores are calculated differently one ranges from 1- 4 and the other from 24-120. Would I use another analysis to get this answer? ===================== 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 __________ NOD32 3989 (20090406) Information __________ This message was checked by NOD32 antivirus system. http://www.eset.com ===================== 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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