Sheldon wants to study the correlation between the age of a pup, weeks, of a certain breed and its Sheldon has a dog of that breed that just had a litter of four pups. Sheldon records the weight of all of the pups once a week for three months. On the basis of his analysis, he conclusion. what kind of statistical investigation is sheldon preforming ?

- theoretical study
- survey
- observational study
- experimental study