Today I'm going to talk about on accident versus by accident and how language changes.

Reddit Comments Seem to Confirm the Study Results
Barratt’s study is 10 years old and it was relatively small, surveying only about 280 people, but I also found some recent evidence that on accident is relatively common among young people. The people at the website FiveThirtyEight made a tool that shows the frequency of words and phrases in more than a billion Reddit comments. It’s a lot like how you can search Google Books with Google Ngram, but it’s for Reddit, so instead of seeing how words are used in published books, you can see how words are used on the Internet, or at least on Reddit.
Reddit users tend to be young (91% are younger than 35), so you would expect it to be a mix of people who prefer on accident and people who somewhat favor by accident. What you see is that Reddit commenters use by accident about three times as often as on accident, but that’s still a lot of people using on accident.
Why Would People Change What They Say?
An interesting conclusion from Barratt's paper is that although there are some hypotheses, nobody really knows why younger people all over the U.S. started saying on accident instead of by accident. For example, there's the idea that on accident is parallel to on purpose, but nobody has proven that children all across the country started speaking differently from their parents because they were seeking parallelism.
Neal Whitman, a linguist and regular Grammar Girl contributor, speculated that the change could have come from a mishearing of an accident—for example, children mishearing It was an accident as It was on accident. But he also admits that this theory also doesn’t explain why on accident seemed to suddenly become the norm in people born after 1995.