What’s the evidence for anything software engineers use? Tests, type checkers, syntax highlighting, IDEs, code review, pair programming, and so on.
In my experience, evidence for the efficacy of software engineering practices falls into two categories:
- the intuitions of developers, based in their experiences.
- scientific studies, which are unconvincing. Some are unconvincing because they attempt to measure the productivity of working software engineers, which is difficult; you have to rely on qualitative measures like manager evaluations or quantitative but meaningless measures like LOC or tickets closed. Others are unconvincing because they instead measure the practice against some well defined task (like a coding puzzle) that is totally unlike actual software engineering.
Evidence for this LLM pattern is the same. Some developers have an intuition it works better.
Also, lines of code is not completely meaningless metric. What one should measure is lines of code that is not verified by compiler. E.g., in C++ you cannot have unbalanced brackets or use incorrectly typed value, but you still may have off-by-one error.
Given all that, you can measure customer facing defect density and compare different tools, whether they are programming languages, IDEs or LLM-supported workflow.