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Should We Trust the Stars?

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A blonde woman and a blond man standing in front of a book shelf and holding four large paper stars in their hands © Felix Schmale/TU Dort­mund
Dr. Sarah Köcher and Dr. Sören Köcher from the Marketing Department of the Faculty of Economics at TU Dort­mund University investigated the meaning of the number of stars that signify the average customer ratings.

Especially at Christmas time, online shopping is a popular way to purchase presents. Before people click to buy, they usually look at the reviews of other customers who have already bought the desired product or tested the desired service. But how meaningful is the number of stars that signify the average customer ratings? Should we blindly trust others’ assessments? Dr. Sarah Köcher and Dr. Sören Köcher from the Marketing Department of the Faculty of Economics at TU Dort­mund University investigated these questions in a study. The research results were published in the current issue of the Journal of Marketing Behavior.

In order to establish a measure of “objective” product quality, the author team collected test results from Stiftung Warentest for a total of 2,473 electronic products in more than 300 product categories, which were tested between 2014 and 2017. In a next step, the test results were combined with the average ratings given to the products by Amazon customers. Ultimately, the scientists were able to compare the test results and ratings of 1,322 products in 224 categories – including televisions, smartphones and vacuum cleaners, for example.

The survey shows that average customer ratings are not necessarily a good measure of the “objective” quality of a product, although they are used by customers as a key criterion in product evaluation. “Only in 69 out of the 224 tested categories was the test winner at Stiftung Warentest also the product with the best average rating on Amazon. This means that you do not necessarily buy a good product if you choose a product with a high average rating,“ said Dr. Sarah Köcher. Overall, the online shoppers’ assessments were therefore hardly consistent with the results of Stiftung Warentest. The researchers also found that the longer a product is on the market, the less the correlation between evaluated and objective quality. With older products, there is no longer any demonstrable correlation between test ratings and average customer ratings.

Another result of the marketing study is that better customer ratings obfuscate the view of buyers on the actual quality of products: the higher the average rating, the less the purchasing decisions are influenced by the actual product quality.

“It is not just that average customer ratings are a rather poor indicator of the quality of a product,” said Dr. Sören Köcher. “To a certain extent, high average ratings even seem to obscure the actual quality of a product.”

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Location & approach

The campus of TU Dort­mund University is located close to interstate junction Dort­mund West, where the Sauerlandlinie A 45 (Frankfurt-Dort­mund) crosses the Ruhrschnellweg B 1 / A 40. The best interstate exit to take from A 45 is "Dort­mund-Eichlinghofen" (closer to Campus Süd), and from B 1 / A 40 "Dort­mund-Dorstfeld" (closer to Campus Nord). Signs for the university are located at both exits. Also, there is a new exit before you pass over the B 1-bridge leading into Dort­mund.

To get from Campus Nord to Campus Süd by car, there is the connection via Vogelpothsweg/Baroper Straße. We recommend you leave your car on one of the parking lots at Campus Nord and use the H-Bahn (suspended monorail system), which conveniently connects the two campuses.

TU Dort­mund University has its own train station ("Dort­mund Universität"). From there, suburban trains (S-Bahn) leave for Dort­mund main station ("Dort­mund Hauptbahnhof") and Düsseldorf main station via the "Düsseldorf Airport Train Station" (take S-Bahn number 1, which leaves every 20 or 30 minutes). The university is easily reached from Bochum, Essen, Mülheim an der Ruhr and Duisburg.

You can also take the bus or subway train from Dort­mund city to the university: From Dort­mund main station, you can take any train bound for the Station "Stadtgarten", usually lines U41, U45, U 47 and U49. At "Stadtgarten" you switch trains and get on line U42 towards "Hombruch". Look out for the Station "An der Palmweide". From the bus stop just across the road, busses bound for TU Dort­mund University leave every ten minutes (445, 447 and 462). Another option is to take the subway routes U41, U45, U47 and U49 from Dort­mund main station to the stop "Dort­mund Kampstraße". From there, take U43 or U44 to the stop "Dort­mund Wittener Straße". Switch to bus line 447 and get off at "Dort­mund Universität S".

Dort­mund Airport offers flights to several destinations in Central Europe. There are regular connections to Katowice, Kraków, London and Munich. For the approximately 20km-trip from Dort­mund Airport to TU Dort­mund University, you can use a shuttle bus to the railway Station "Bahnhof Holzwickede", from which trains depart to Dort­mund main station (please visit Verkehrsverbund Rhein-Ruhr for more information). Normally, the fastest way is to catch a taxi at Dort­mund Airport.

The H-Bahn is one of the hallmarks of TU Dort­mund University. There are two stations on Campus Nord. One ("Dort­mund Universität S") is directly located at the suburban train stop, which connects the university directly with the city of Dort­mund and the rest of the Ruhr Area. Also from this station, there are connections to the "Technologiepark" and (via Campus Süd) Eichlinghofen. The other station is located at the dining hall at Campus Nord and offers a direct connection to Campus Süd every five minutes.