First i would like to say mythbusters is a great show and they usually approach there myths in scientific (often entertaining ways). This time I think they did a fairly decent job testing the myth of yawning being contagious. They stated that the myth was proven because they recorded that 29% of the subjects with stimulus yawned and 25% of the subjects without stimulus yawned as well. Mythbusters decided to confirm the myth due to a large sample size.
I think they kept the subjects exposed to stimulus too isolated. I think that the experiment would have yielded more tangible results if the subjects exposed to the stimulus were put into a room together and were all exposed to the stimulus simultaneously. If yawning was contagious then this would let us see a ripple effect in the room. You could then repeat this process with fresh participants as many times as you would like until you feel you have tested a large enough sample size.
The downside to using my method is that it doesn’t test a group without the stimulus. Also if someone were to try to to test a non stimulus group there is the off chance that someone could yawn in the room and invalidate the control group. So in that respect the mythbusters method to test their subjects one at a time is a more reliable and harder to be invalidated.
While this was an interesting experiment but we still don’t know why people seem to be effected by others yawning. I am curious to see if there is a scientific explanation to support that myth.