Answer: d)They have not defined happiness or how it will be measured.
Explanation: A survey is the record that is formed on the basis of through examination and observation of any particular situation or thing. The survey carried out by Magali and Jean has a major flaw because it does not have any certain parameter for measuring the rate of happiness in people present in the mall.
Other options are not appropriate to be a mistake in survey because people will not avoid the participation, the experimental survey data is valid and dependency is not based on population of people in mall.Thus, the correct option is option(d).