> 
> zylktrt <- factor(zylktrt)
> timeprd <- factor(timeprd)
> cat_id <- factor(cat_id)
> 
> tapply(score,zylktrt,mean)
       0        1 
10.58824 13.58824 
> tapply(score,timeprd,mean)
       1        2        3        4        5 
10.00000 11.14706 12.23529 13.29412 13.76471 
> tapply(score,list(zylktrt,timeprd),mean)
          1        2        3        4        5
0  9.058824 10.17647 10.88235 11.41176 11.41176
1 10.941176 12.11765 13.58824 15.17647 16.11765
> 
> interaction.plot(timeprd,zylktrt,score)
> 
> cat.mod1 <- aov(score ~ zylktrt + zylktrt/cat_id + timeprd + zylktrt:timeprd)
> summary(cat.mod1)
                 Df  Sum Sq Mean Sq  F value    Pr(>F)    
zylktrt           1  382.50  382.50 126.0251 < 2.2e-16 ***
timeprd           4  324.12   81.03  26.6974 4.137e-16 ***
zylktrt:cat_id   32 2131.98   66.62  21.9512 < 2.2e-16 ***
zylktrt:timeprd   4   50.59   12.65   4.1669  0.003316 ** 
Residuals       128  388.49    3.04                       
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
> 
> cat.mod2 <- aov(score ~ zylktrt*timeprd + Error(zylktrt/cat_id))
Warning message:
In aov(score ~ zylktrt * timeprd + Error(zylktrt/cat_id)) :
  Error() model is singular
> summary(cat.mod2)

Error: zylktrt
        Df Sum Sq Mean Sq
zylktrt  1  382.5   382.5

Error: zylktrt:cat_id
          Df Sum Sq Mean Sq F value Pr(>F)
Residuals 32   2132  66.624               

Error: Within
                 Df Sum Sq Mean Sq F value    Pr(>F)    
timeprd           4 324.12  81.029 26.6974 4.137e-16 ***
zylktrt:timeprd   4  50.59  12.647  4.1669  0.003316 ** 
Residuals       128 388.49   3.035                      
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
>