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?

 the most serious flaw of this design is: They have not defined happiness or how it will be measured.
Happiness is very subjective because it each person may have a different source of happiness. For some people, it maybe the success of their career while for the other it's simply doing what they love to do. Not only that, if Magali and Jane collect the data simply by asking like that, they would not know whether the person is telling the truth.