F1
a numeric vector containing a factor with three modalities
F2
a numeric vector containing a continuous variable
F3
a numeric vector containing a factor with two modalities
F4
a numeric vector containing a continuous variable
Parasite1
a numeric vector containing the serological status to the first parasite
Parasite2
a numeric vector containing the serological status to the second parasite
AGE
a numeric vector containing a factor with three modalities indicating the age classes