Hallo,
I suppose that my question is quite simple. I'm really new with mixed model... and I'm not an expert in statistics.

I'm using lmerTest library

My mixed model looks like:

Model = lmer(rt~Trial+letters+w.pw*group*XX+ (1|Sj)+(0+Trial|Sj)+(0+letters|Sj)+(1|Word),lex)

The summary of fixed effect:

Fixed effects:
                              Estimate Std. Error t value Pr(>|t|)
(Intercept)                  6.548e+00  5.886e-02  111.26  < 2e-16 ***
Trial                       -7.972e-05  8.006e-06   -9.96       NA
letters                      2.066e-02  7.554e-03    2.73  0.00677 **
w.pwW                       -1.479e-01  2.769e-02   -5.34 1.84e-07 ***
groupB             -3.452e-02  4.316e-02   -0.80  0.42915
XX                       -3.398e-04  3.565e-04   -0.95  0.34134
w.pwW:groupB        4.923e-02  1.965e-02    2.51  0.01227 *
w.pwW:XX                  2.912e-04  5.037e-04    0.58  0.56366
groupB:XX        5.499e-04  2.544e-04    2.16  0.03067 *
w.pwW:groupB:XX -4.788e-04  3.578e-04   -1.34  0.18091

Perfmorming the anova the interaction :



anova(lex.lmer4)

[1] "Asymptotic covariance matrix A is not positive!"

Analysis of Variance Table of type 3 with  Satterthwaite  approximation for degrees of freedom

                 Df Sum Sq Mean Sq F value  Denom    Pr(>F)

Trial             1 3.1433  3.1433 99.1516    0.0

letters           1 0.2319  0.2319  7.4795  212.4  0.006768 **

w.pw              1 3.7704  3.7704 22.6744  222.6 3.457e-06 ***

group             1 0.0004  0.0004  0.0555   32.5  0.815311

XX             1 0.0009  0.0009  0.0273  222.8  0.868969

w.pw:group        1 0.2897  0.2897  6.2753 6867.2  0.012266 *

w.pw:XX        1 0.0004  0.0004  0.0121  222.9  0.912584

group:XX       1 0.0949  0.0949  3.0108 6867.2  0.082756 .

w.pw:group:XX  1 0.0574  0.0574  1.7905 6867.1  0.180910

---

Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Warning message:

In pf(F.stat, qr(Lc)$rank, nu.F) : Si è prodotto un NaN


Why do I fail to reach significance in the interaction group*XX while it seems to be significant in the summary?

Thanks a lot
Tania




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