26 Nov 01:57 2014

### covariate or predictor

Kristi Glover <kristi.glover <at> hotmail.com>

2014-11-26 00:57:44 GMT

2014-11-26 00:57:44 GMT

Hi, I am wondering how I can separate whether it is covariate or predictor in the ANOVA analysis. For example A<-structure(list(Machine = c(1L, 1L, 1L, 1L, 1L, 2L, 2L, 2L, 2L, 2L, 3L, 3L, 3L, 3L, 3L), Diameter = c(20L, 25L, 24L, 25L, 32L, 22L, 28L, 22L, 30L, 28L, 21L, 23L, 26L, 21L, 15L), Strength = c(36L, 41L, 39L, 42L, 49L, 40L, 48L, 39L, 45L, 44L, 35L, 37L, 42L, 34L, 32L)), .Names = c("Machine", "Diameter", "Strength"), class = "data.frame", row.names = c(NA, -15L)) attach(A) b<-aov(Strength~Diameter) summary(b) c<-aov(Strength~Diameter+as.factor(Machine)) summary(c) I am confused here whether the "Mechine" is covariate or predictor. How do I know which one is covariate and predictor? If Machine is predictor (just like Diameter), how I am supposed to write in the model? is the equation (below) for this one in the condition that the Machine is predictor? c1<-aov(Strength~Diameter+Machine), ?????. If it is so, it means that co-variate is dummy variable, right???? Your help will really help me to clear the concept. Thanks KG [[alternative HTML version deleted]]