The results are in and dishwashers are more effective at cleaning dirty dishes than hand washing, according to an article in Atlantic Monthly. 

Their main edge over traditional elbow grease? Water temperature.

It turns out that water must be at least 145 degrees Fahrenheit to effectively sanitize dishes.  Most dishwashers run water temperatures between 130 and 170 degrees, but human hands often cannot tolerate water over 104 degrees and the sponges used to hand-wash dishes are often teeming with bacteria.

For people who do not have a dishwasher, experts recommend using dishwashing gloves so the water temperature can be higher, and periodically sanitizing their sponges by microwaving it for 30 seconds.