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POChange intercept using lmer function in R
 

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  1. POChange intercept using lmer function in R
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    <p>I am trying to use the lmer function to investigate if there is an interaction effect on the reaction time (RT) between 3 different conditions (cond=0, 1, 2) and the presence of the target (target=False or True) in patients (Patient). </p> <p>I wrote the following equation: </p> <pre><code>lmer(RT~cond*target+(1|Patient)) </code></pre> <p>My problem is that the default intercept for this function is cond = 0 and target = False, whereas I would like the intercept to be cond= 0 and target=True (in order to see if there is a significant difference between cond0*target=True and cond1*target=True). </p> <p>I would really appreciate your help.</p> <p>Here is the output I have </p> <pre><code>stu3&lt;-lmer(RT~cond*target+(1|Patient), data=subset(ss, Groupe=="ugs" &amp; primeable ==TRUE &amp; Correct==TRUE &amp; NoPrac==TRUE)) pvals.fnc(stu3) $fixed Estimate MCMCmean HPD95lower HPD95upper pMCMC Pr(&gt;|t|) (Intercept) 0.5511 0.5513 0.5258 0.5807 0.0001 0.0000 cond1 0.0618 0.0619 0.0498 0.0741 0.0001 0.0000 cond2 0.0285 0.0285 0.0142 0.0438 0.0002 0.0001 targetFALSE 0.1389 0.1389 0.1239 0.1549 0.0001 0.0000 cond1:targetFALSE -0.0752 -0.0751 -0.0943 -0.0545 0.0001 0.0000 cond2:targetFALSE -0.0788 -0.0786 -0.0998 -0.0564 0.0001 0.0000 $random Groups Name Std.Dev. MCMCmedian MCMCmean HPD95lower HPD95upper 1 Patient (Intercept) 0.0610 0.0583 0.0599 0.0425 0.0797 2 Residual 0.1674 0.1674 0.1674 0.1650 0.1699 </code></pre> <p>Based on my data, the intercept being chosen is <code>cond0:targetTRUE</code> and the other levels in the output are <code>cond1:targetFALSE</code> and <code>cond2:targetFALSE</code>.</p>
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    1. COso the `cond1` parameter should exactly correspond to a test of the difference between `cond==0` and `cond==1` when `target` is `TRUE` (provided that you haven't done anything else clever with your contrasts ...), which is what it sounds like you wanted.
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