The phrase "a mistake in how" is correct and usable in written English.
You can use it when discussing errors related to methods or processes.
Example: "There was a mistake in how the data was analyzed, leading to incorrect conclusions."
Alternatives: "an error in the way" or "a flaw in the method".
Then later: "I made a mistake in how I talk about the war.
At least Goldman was forced to state that its disclosures "contained incomplete information" and that it made a "mistake" in how it marketed the securities.
"There's always another side, but it looks like they may have made a mistake in how it was handled," he says.
Mr. Kerry shot back: "I made a mistake in how I talked about the war, but the president made a mistake in invading Iraq.
"Well, you know, when I talked about the $87 billion, I made a mistake in how I talk about the war," Mr. Kerry said.
"We are acutely aware of it, and are watching very carefully to be sure we aren't making a mistake in how we are apportioning our resources".
This might have protected what appears to be a basic mistake in how Samsung integrated SwiftKey on their devices.
Somewhere someone made a fatal mistake in how many new Democrats and voters would come out to the polling booths.
But he said he had made an honest mistake in how he remembered the encounter.
For nearly 20 years the work-life field made a mistake in thinking about how to solve this problem.
They've generally trailed Facebook in taking risks with new products (News Feed, self serve ads, Facebook Connect), and they made a crucial strategic mistake in how they handled international expansion (Facebook gets its own users to create local translations of the site, MySpace opens offices in every country they want a presence in – guess which one scales).
