An experiment was carried out in order to investigate the migration of nematodes in Danish herrings. The fish were allocated to eight different treatment groups corresponding to different combinations of storage time and storage conditions until filleting. After filleting, it was determined whether nematodes were present in the fillet or not.
A data frame with 884 observations on the following 4 variables.
a numeric vector that is the combination of storage and time
a numeric vector that contains the duration of storage in hours before the fish is filleted
a numeric vector representing the storage condition
a numeric vector to indicate the presence of nematodes (1) or absence of nematodes (0)
The variable group is the combination of storage condition and storage time. Notice that a storage time 0 is equivalent to storage condition 0 and that no fish were stored 132 hours under condition 4. Hence, there are only 8 combinations; i.e., 8 levels of the group variable.
A. Roepstorff and H. Karl and B. Bloemsma and H. H. Huss (1993). Catch handling and the possible migration of Anisakis larvae in herring, Clupea harengus. Journal of Food Protection. 56:783-787.