Answer:
Explanation:
Hello!
The research hypothesis is that "The new advertisement increases the likelihood of people buying the new  mechanical toy dogs"
The new campaign is designed to be persuasive to people with a certain personality profile.
To test her hypothesis, the doctor choose 4 groups of participants and asked them whether they were interested in acquiring the toy before and after watching the advertisement.
The clear limitation in this trial is the failure of taking a representative sample. There are several confounding factors not taken into account, such as social status of the participants (if they can or cannot afford the toy), family status (people with children are more likely to buy toys than childless adults).
It is possible that the people assigned to each group had different propensity for acquiring the toys and that these groups  were unbalanced, producing bias in the conclusions extracted from this trial.
I hope this helps!
