If you find two errors on a page there will be more.

Randy Murray is a professional copywriter and a diehard blogger, and he touched upon a rule today that is true for any form of quality testing, and an important principle in software testing:

Here’s my rule of thumb: if you find two errors on a page, there are probably more.

I first learned about this pattern when I taught an expository writing course as a grad student and graded a LOT of papers. It’s not a law. You won’t invariably find more errors. It’s just a sign that there are probably more problems with the page of copy and it’s a big red flag waving at you as an editor to pay closer attention.

When you're working on larger, more complex software with a wide set of features and complex requirements it becomes critically important to ensure that the design documentation is accurate. A problem costs less, in terms of development resources as well as financially, to rectify the earlier in the development lifecycle it is found. The majority of significant errors occur in the translation of the requirements/design documentation into actual working code. Any mistake or ambiguity in those documents therefore is an expensive problem to remedy by the time you get to system testing, which is where most bugs are found.

You are potentially dealing with tens if not hundreds of pages of text however, and therefore do not want to arduously review every sentence time and time again as the document goes through revision. Understanding the rule that Randy highlights therefore allows a sample to be tested. The proofreader can take a few pages and thoroughly highlight every issue in that text. The document author can then use to make educated revisions to the whole document; in theory eliminating similar mistakes throughout the whole text. A different sample is then chosen and the process repeats until the hit rate on flaws is sufficiently low to allow the presumption that the document has reached sufficient quality.

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