topic Re: Dunnett's Test Statistic in Discussions
https://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/223787#M44519
<P>I've put together some fake data to illustrate what is going on:</P>
<P> </P>
<P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="dunnetts.PNG" style="width: 917px;"><img src="https://community.jmp.com/t5/image/serverpage/image-id/19047i85C6BAD174D7D451/image-size/large?v=v2&px=999" role="button" title="dunnetts.PNG" alt="dunnetts.PNG" /></span></P>
<P> </P>
<P>I've chosen the data such thast the contrast between c and the control (a) has a p-value of 0.05 i.e. the threshold at which we are assessing statistical significance. </P>
<P> </P>
<P>A t-statistic can be calculated as a the ratio of the difference to the standard error of the difference. For the second contrast the statistic is 2.5 i.e. the Q statistic. So whilst there is a statistic for each comparison, we can define a single statistic to that is the threshold for statistical significance.</P>
<P> </P>
<P>You can check Wiki for references on the method although there is a tendency for Wiki to be overly abstract for statistical methods but you should easily be able to search for other explanations, e.g.</P>
<P><A href="http://davidmlane.com/hyperstat/B112114.html" target="_blank">http://davidmlane.com/hyperstat/B112114.html</A></P>Wed, 28 Aug 2019 11:38:27 GMTDavid_Burnham2019-08-28T11:38:27ZDunnett's Test Statistic
https://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222728#M44442
<P>I have run an ANOVA in JMP with a Dunnett's post hoc test to compare 8 treatments to my control. In a publication I am working on I reported the p-values for each comparison to the control. A reviewer has asked me to include the test statistic along with the p-values. For some reason, a test statistic is not displayed along with the p-values in the default settings on the Dunnett's output within the fit model personality. I'm new to statistics so I'm not even certain what the test statistic is for a Dunnett's procedure. Does anyone know what that test statistic would be and how I can get JMP to display it?</P>Thu, 22 Aug 2019 19:47:07 GMThttps://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222728#M44442Mananahi2019-08-22T19:47:07ZRe: Dunnett's Test Statistic
https://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222795#M44451
<P>Hi, </P><P> </P><P>I think you may be able to get what the reviewer is asking by performing your test in the "Fit Model" analysis instead of the "Y by X".</P><P> </P><P>Here is a simple example with dummy data (Y) for 3 categorical levels (X)</P><P> </P><P>Go to Analysis > Fit Model and assign your Y and X as shown:</P><P> <span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="Fit Model Simple ONEWAY.PNG" style="width: 400px;"><img src="https://community.jmp.com/t5/image/serverpage/image-id/18955i76533B6F6B8A31AD/image-size/medium?v=v2&px=400" role="button" title="Fit Model Simple ONEWAY.PNG" alt="Fit Model Simple ONEWAY.PNG" /></span></P><P>Click Run, and in the model result, go to GROUP effect > Dunnett's</P><P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="Sub Menu Dunnet's in Fit Model Result.PNG" style="width: 400px;"><img src="https://community.jmp.com/t5/image/serverpage/image-id/18956i14A471F7FD2F4173/image-size/medium?v=v2&px=400" role="button" title="Sub Menu Dunnet's in Fit Model Result.PNG" alt="Sub Menu Dunnet's in Fit Model Result.PNG" /></span></P><P>The resulting screen in giving you the full test statistics (LS Means Differences Dunnett's) as shown in this final screenshot:</P><P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="Dunnet Test Statitics in Fit Model.jpg" style="width: 999px;"><img src="https://community.jmp.com/t5/image/serverpage/image-id/18957i1B9DB568E97DD420/image-size/large?v=v2&px=999" role="button" title="Dunnet Test Statitics in Fit Model.jpg" alt="Dunnet Test Statitics in Fit Model.jpg" /></span></P><P>That should satisfy the reviewer. If it does not, you should try to clarify what he/she means by Test Statistics.</P><P> </P><P>TS</P>Fri, 23 Aug 2019 01:58:35 GMThttps://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222795#M44451Thierry_S2019-08-23T01:58:35ZRe: Dunnett's Test Statistic
https://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222880#M44468
So I'm looking at the LS Means Differences Dunnett's table on your screenshot and it has columns for Level, -Level, Difference, Std Err Dif, Lower CL, Upper CL, and p-Value. Shouldn't there be one more column in there that says t-Statistic (or some other test statisctic) next to the p-value so that we know what was used to calculate that p-value. Something like that seems to be on most JMP outputs. That's what I think I am looking for, but maybe I just don't understand stats and am assuming that something exists. Do Dunnett's procedures not have test statistics?Fri, 23 Aug 2019 18:12:05 GMThttps://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222880#M44468Mananahi2019-08-23T18:12:05ZRe: Dunnett's Test Statistic
https://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222973#M44485
I believe what you are looking for is the Q value shown in the LSMeans Difference Dunnett table (equivalent to t statistics but for multiple comparison to a control value).<BR />If this not what you are looking for, then I'm afraid that I will not be able to help you any further.<BR />TSSat, 24 Aug 2019 23:34:23 GMThttps://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222973#M44485Thierry_S2019-08-24T23:34:23ZRe: Dunnett's Test Statistic
https://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222974#M44486
I think that is what I'm looking for. thanks. I'm still a little confused though. Why is there only one statistic for the whole table. Most tables have an individual test statistic for each p-value. Can you or anyone enlighten me to why Dunnett's would be different?<BR />Sun, 25 Aug 2019 00:21:39 GMThttps://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/222974#M44486Mananahi2019-08-25T00:21:39ZRe: Dunnett's Test Statistic
https://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/223787#M44519
<P>I've put together some fake data to illustrate what is going on:</P>
<P> </P>
<P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="dunnetts.PNG" style="width: 917px;"><img src="https://community.jmp.com/t5/image/serverpage/image-id/19047i85C6BAD174D7D451/image-size/large?v=v2&px=999" role="button" title="dunnetts.PNG" alt="dunnetts.PNG" /></span></P>
<P> </P>
<P>I've chosen the data such thast the contrast between c and the control (a) has a p-value of 0.05 i.e. the threshold at which we are assessing statistical significance. </P>
<P> </P>
<P>A t-statistic can be calculated as a the ratio of the difference to the standard error of the difference. For the second contrast the statistic is 2.5 i.e. the Q statistic. So whilst there is a statistic for each comparison, we can define a single statistic to that is the threshold for statistical significance.</P>
<P> </P>
<P>You can check Wiki for references on the method although there is a tendency for Wiki to be overly abstract for statistical methods but you should easily be able to search for other explanations, e.g.</P>
<P><A href="http://davidmlane.com/hyperstat/B112114.html" target="_blank">http://davidmlane.com/hyperstat/B112114.html</A></P>Wed, 28 Aug 2019 11:38:27 GMThttps://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/223787#M44519David_Burnham2019-08-28T11:38:27ZRe: Dunnett's Test Statistic
https://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/223789#M44520
<P>Also I should have mentioned JMP's online help:</P>
<P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="dunnetts2.PNG" style="width: 999px;"><img src="https://community.jmp.com/t5/image/serverpage/image-id/19048iA202520768F1520A/image-size/large?v=v2&px=999" role="button" title="dunnetts2.PNG" alt="dunnetts2.PNG" /></span></P>
<P><A href="https://www.jmp.com/support/help/14-2/effect-details.shtml#625536" target="_blank">https://www.jmp.com/support/help/14-2/effect-details.shtml#625536</A></P>
<P> </P>Wed, 28 Aug 2019 11:43:02 GMThttps://community.jmp.com/t5/Discussions/Dunnett-s-Test-Statistic/m-p/223789#M44520David_Burnham2019-08-28T11:43:02Z