Tampering in the context of a controlled process is adjusting the process on the basis of outcomes which are within the expected range of variability. The net result is to re-align the process so that an increased proportion of the output is out of specification. The term was introduced in this context by W. Edwards Deming, and he was a strong proponent of using control charts to avoid tampering.
See also Incentive program Control chart
References W. Edwards Deming (1994) The New Economics for Industry, Government, Education, 2nd edition, Massachusetts Inst Technology. ISBN 0-911379-07-X (Chapter 9.) Deming, W. Edward (1986), Out of the Crisis, MIT Center for Advanced Engineering Study, 327–32. (2000 edition: ISBN 0-262-54115-7) Gitlow, Howard; Gitlow, Shelly; Oppenheim, Alan; Oppenheim, Rosa (1989), Tools and Methods for The Improvement of Quality, CRC Press ISBN 0-256-05680-3 Krehbiel, T. C. (1994), "Tampering with a Stable Process". Teaching Statistics, 16, 75–79. doi:10.1111/j.1467-9639.1994.tb00696.x