Are there statistics on software quality improvement methods?

Question

Project management

Are there such statistics on methods, for example:
- the introduction of Unit testing reduces the number of bugs by X%, support costs by Y%, ...
- Code-Review
- Agile / SCRUM
- other methods
It is desirable to present some qualitative characteristics, in percentages, pieces, maybe in some other units.
A cursory search did not find such statistics.

Answer 1

I found an article talking about research in 2007. The article says that around this time, Agile methodologies were recognized as widely used.
Why do you need an answer to this question?
If you want to argue with someone, then this is a waste of time.
If you want to convince your bosses to try Agile, then it is better to demonstrate the real results obtained by your team.
The best statistics are the statistics collected by your team before and after the implementation of the chosen methodology.

Answer 2

Making Software :

Are some programmers really ten times more productive than others?
Does writing tests first help you develop better code faster?
Can code metrics predict the number of bugs in a piece of software?
Do design patterns actually make better software?
What effect does personality have on pair programming?
What matters more: how far apart people are geographically, or how far apart they are in the org chart?