Referring back to June’s column, I hope you’ve found C. M. Hendrix’s “ways to mess up an experiment” helpful in putting your design of experiments training into a much better perspective. Today, I’m going to add two common mess-ups from my consulting experience. If you’re not careful, it’s all too easy to end up with data that’s worthless.

Balestracci’s Mess-Up No. 1

Underestimating the unintended ingenuity of human psychology will mess up your experiment—and this includes the study planners! 

Trust me, there is no way you could make up the things busy people will do to (unintentionally) mess up your design and its data. “But I just want to run a simple 2 × 2 × 2 factorial,” someone might say.

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