<div>Hi,</div>
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<div>I've recently started using R to do regressions, using the 'lmer' function. I am currently re-running some analyses that originally had treatment coding, so that they now have contrast coding. My question is about how to interpret contrast coded regression outputs. <br>
<br>One of my independent variables (<font face="tahoma,sans-serif">nativeLanguage) has 3 levels: English, Chinese, and Korean. As this experiment was conducted in English, participants in the English group were native speakers, and participants in the other two groups were non-native speakers. In my original treatment-coded analysis, English was the reference level. My output for e.g. 'langCompare.lmer = lmer(duration~nativeLanguage+(1|Subject), data=myData)' had lines like:</font></div>
<div><br><font face="tahoma,sans-serif"> Estimate Std. Error t value</font><br>nativeLanguageChinese 0.025920 0.002384 10.872</div>
<div>nativeLanguageKorean -0.004416 0.002091 -2.112</div>
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<div>As I understood it, such lines gave information about the comparison between Chinese and English, and between Korean and English, respectively. </div>
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<div>I contrast coded this variable with the code: 'contrasts(myData$nativeLanguage) = c(-1, .5, .5)' (after ordering the levels: English, Chinese, Korean). This was in order to compare the native (English) group to the non-native (Chinese and Korean) groups. After this contrast coding, my output had lines like:</div>
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<div> Estimate Std. Error t value<br>nativeLanguage1 0.10002 0.010113 11.242
<div>nativeLanguage2 -0.00046 0.639887 1.388</div>
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<div>I was wondering how to interpret this output. My guess is that nativeLanguage1 is the comparison between the native and non-native groups, and native_language2 is the comparison between Chinese and Korean, but I haven't been able to find any resources to confirm this. </div>
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<div>I would greatly appreciate any advice on how to interpret regressions after contrast coding, or pointers to appropriate resources on this topic!</div>
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<div>Thanks very much,</div>
<div>Rachel </div></div>