The article “Popping Cork Sound Makes Wine Taste Better” (decanter.com/wine-news/popping-cork -sound-makes-wine-taste-better-experiment -377364, retrieved February 11, 2018) describes a study in which 140 people were assigned to one of two groups. Those in one group heard the noise made by a bottle of wine being uncorked before tasting a glass of wine. Those in the other group heard the noise made by a person releasing a screw cap before tasting a glass of wine. Both groups tasted the same wine. It was reported that the average rating was higher for the group that heard the cork popping than the average rating for the group that heard the screw cap being released. 

a. Is the study described an observational study or an experiment? 

b. Can a case be made for the researcher’s conclusion that hearing a cork pop rather than a screw cap being released was the cause for the higher rating? Explain.