She uses a convenience sampling, hence, she cannot make valid generalizations about the pets owned by families in her town because her street may differ from the rest of town, due to economic factors for example.
How are samples classified?
Samples may be classified as:
- Convenient: Drawn from a conveniently available pool.
- Random: All the options into a hat and drawn some of them.
- Systematic: Every kth element is taken.
- Cluster: Divides population into groups, called clusters, and each element in the cluster is surveyed.
- Stratified: Also divides the population into groups. Then, a equal proportion of each group is surveyed.
Here, the residents of her street are the easiest sample, that is convenience, but since there may be things such as economic factors in play, her street may be different from the rest of the town, hence she cannot make valid generalizations about the pets owned by families in her town.
More can be learned about sampling concepts at
