Trying to show association between musical education and grades. Simply observed students in the wild no survey . In these studies, researchers don"t assign choices, instead they simply observe them. In addition, this was a retrospective study because first, the researchers identified students who study music and then collected data on their past grades. Doing this for just one school may not be representative of the entire country if it is done for just one year. Observational studies are valuable for discovering trends and possible relationships. Since retrospective studies are based on historical data, they can have errors. A better approach would be to observe individuals overtime. Identifying subjects in advance and collecting data as events unfold would make this a prospective study. You can prove a cause and effect relationship. Could have students and force half to take music and not allow the other half to take it and compare their grades several years later.