How the bandwagon effect occurs is demonstrated by the history of measurements of the speed of light. Because this speed is the basis of the theory of relativity, it’s one of the most frequently and carefully measured ① quantities in science. As far as we know, the speed hasn’t changed over time. However, from 1870 to 1900, all the experiments found speeds that were too high. Then, from 1900 to 1950, the ② opposite happened ― all the experiments found speeds that were too low! This kind of error, where results are always on one side of the real value, is called “bias.” It probably happened because over time, experimenters subconsciously adjusted their results to ③ match what they expected to find. If a result fit what they expected, they kept it. If a result didn’t fit, they threw it out. They weren’t being intentionally dishonest, just ④ influenced by the conventional wisdom. The pattern only changed when someone ⑤ lacked the courage to report what was actually measured instead of what was expected.

* bandwagon effect: 편승 효과