An article recently appeared on npr.org's music page with a headline beggin the question "Do Orchestras Really Need Conductors?" The article, by Shankar Vedantam, reports the findings of a recent study attempting to scientifically determine the relationship between the conductors movements on the podium and the string players' bow movements. According to the article, the study concluded not only that the conductors movements predicted the movements of the players bows, but that audience members find music conducted by professionals to be more aesthetically pleasing than music conducted by amateurs.
The implication of this article is that the answer to the titular question is "yes", but the study was not aimed at answering the question at all. All the study showed is that when there is a conductor, he or she can influence how the orchestra plays, and, the former being true, that better conductors yield better musical results. To answer the question "Do Orchestras Really Need Conductors?" would require a control group. How does a professional orchestra sound without any conductor at all?
Luckily for us, some data regarding that question already exists. Groups such as the Orpheus Chamber Orchestra regularly perform without the assistance of a conductor. In addition to its Grammy Awards, the orchestra has been named to The WorldBlu List of Most Democratic Workplaces for six years running. For an orchestra the size of Orpheus (comprising 34 musicians), it is quite clear that a conductor is not necessary.
The question raised by this article is one worth examining, but to call this study scientific proof that orchestras need conductors is to ignore the definition of science. The better question would be "When does an orchestra need a conductor?" - the answer to which I doubt will present itself in numerical form."