> 
> tapply(strength,agg,mean)
   Basalt Silicious 
 93.66667  72.62500 
> tapply(strength,knead,mean)
 Regular      Low Very Low 
  109.40    83.00    45.25 
> tapply(strength,list(agg,knead),mean)
          Regular      Low Very Low
Basalt        107 97.33333 56.00000
Silicious     111 61.50000 41.66667
> 
> options(contrasts=c("contr.sum","contr.poly"))
> 
> tensile.mod1 <- aov(strength ~ agg + knead + agg:knead)
> summary(tensile.mod1)
            Df Sum Sq Mean Sq F value    Pr(>F)    
agg          1 1518.0  1518.0 135.184 2.726e-06 ***
knead        2 8401.9  4201.0 374.112 1.252e-08 ***
agg:knead    2  953.4   476.7  42.454 5.497e-05 ***
Residuals    8   89.8    11.2                      
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
> 
> library(car)
Loading required package: MASS
Loading required package: nnet
Loading required package: survival
Loading required package: splines
Warning message:
package 'car' was built under R version 2.12.1 
> 
> Anova(tensile.mod1,type="III")
Anova Table (Type III tests)

Response: strength
            Sum Sq Df  F value    Pr(>F)    
(Intercept)  75050  1 6683.495 5.589e-13 ***
agg            710  1   63.269 4.551e-05 ***
knead         6806  2  303.070 2.879e-08 ***
agg:knead      953  2   42.454 5.497e-05 ***
Residuals       90  8                       
---
Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1 
>