Hello everybody,
I need an help because I don´t know if the command for the ANOVA analysis I am
performing in R is correct. Indeed using the function aov I get the following
error:"In aov (......) Error() model is singular"
The structure of my table is the following: subject, stimulus, condition, sex,
response
Example:
subject stimulus condition sex response
subject1 gravel EXP1 M 59.8060
subject2 gravel EXP1 M 49.9880
subject3 gravel EXP1 M 73.7420
subject4 gravel EXP1 M 45.5190
subject5 gravel EXP1 M 51.6770
subject6 gravel EXP1 M 42.1760
subject7 gravel EXP1 M 56.1110
subject8 gravel EXP1 M 54.9500
subject9 gravel EXP1 M 62.6920
subject10 gravel EXP1 M 50.7270
subject1 gravel EXP2 M 70.9270
subject2 gravel EXP2 M 61.3200
subject3 gravel EXP2 M 70.2930
subject4 gravel EXP2 M 49.9880
subject5 gravel EXP2 M 69.1670
subject6 gravel EXP2 M 62.2700
subject7 gravel EXP2 M 70.9270
subject8 gravel EXP2 M 63.6770
subject9 gravel EXP2 M 72.4400
subject10 gravel EXP2 M 58.8560
subject11 gravel EXP1 F 46.5750
subject12 gravel EXP1 F 58.1520
subject13 gravel EXP1 F 57.4490
subject14 gravel EXP1 F 59.8770
subject15 gravel EXP1 F 55.5480
subject16 gravel EXP1 F 46.2230
subject17 gravel EXP1 F 63.3260
subject18 gravel EXP1 F 60.6860
subject19 gravel EXP1 F 59.4900
subject20 gravel EXP1 F 52.6630
subject11 gravel EXP2 F 55.7240
subject12 gravel EXP2 F 66.4220
subject13 gravel EXP2 F 65.9300
subject14 gravel EXP2 F 61.8120
subject15 gravel EXP2 F 62.5160
subject16 gravel EXP2 F 65.5780
subject17 gravel EXP2 F 59.5600
subject18 gravel EXP2 F 63.8180
subject19 gravel EXP2 F 61.4250
.....
.....
.....
.....
As you can notice each subject repeated the evaluation in 2 conditions (EXP1
and EXP2).
What I am interested in is to know if there are significant differences between
the evaluations of the males and the females.
This is the command I used to perform the ANOVA with repeated measures:
aov1 = aov(response ~ stimulus*sex + Error(subject/(stimulus*sex)), data=scrd)
summary(aov1)
I get the following error:
> aov1 = aov(response ~ stimulus*sex + Error(subject/(stimulus*sex)),
data=scrd)
Warning message:
In aov(response ~ stimulus * sex + Error(subject/(stimulus * sex)), :
Error() model is singular
> summary(aov1)
Error: subject
Df Sum Sq Mean Sq F value Pr(>F)
sex 1 166.71 166.72 1.273 0.274
Residuals 18 2357.29 130.96
Error: subject:stimulus
Df Sum Sq Mean Sq F value Pr(>F)
stimulus 6 7547.9 1257.98 35.9633 <2e-16 ***
stimulus:sex 6 94.2 15.70 0.4487 0.8445
Residuals 108 3777.8 34.98
---
Signif. codes: 0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1
Error: Within
Df Sum Sq Mean Sq F value Pr(>F)
Residuals 420 9620.6 22.906
>
The thing is that looking at the data it is evident for me that there is a
difference between male and females, because for each stimulus I always get
a mean higher for the males rather than the females.
Therefore the ANOVA should indicate significant differences....
Is there anyone who can suggest me where I am wrong?
Finally, I know that in R there are two libraries on linear mixed models called
nlme and lme4, but I have never used it so far and I don´t know if I have to
utilize it for my case.
Is it the case to utilize it? If yes, could you please provide a quick R example
of a command which could solve my problem?
Thanks in advance!
Best regards
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