Magali and Jean-Gabriel have been asked to design a study investigating happiness across the lifespan. They decide their study will involve going to the mall and asking people of a variety of ages if they are happy or unhappy. What is the most serious flaw of this design?a. People will know that they are part of a research study and may decline participation.
b. Survey data is not as valid as experimental data.
c. Their results will depend on how busy the mall is.
d. They have not defined happiness or how it will be measured.

D). They have not defined happiness or how it will be measured.

Explanation:

As per the question, the most consequential flaw or error in this study design is that 'Jean-Gabriel and Magali have not defined happiness and neither provided a description or method that describes how it will be measured.' This flaw would make the design ineffective as it would not be able to produce reasonable deductions or conclusions because they have decided that 'they would visit a mall to survey people of different ages' but this requires a scale on which they would measure happiness. Since they have not mentioned any such scale which implies that they won't be able to collect data and hence, the study could not be taken forward. Therefore, option D displays the major error of this design that makes it invalid.

they encountered severe weather for which they were poorly prepared.