Which of the following defines a shift in a run chart?

A shift in a run chart is defined as six or more consecutive points lying above or below the median. This criterion indicates a significant change in the pattern of the data being analyzed. When analysts observe this pattern, it suggests that an underlying variation may have occurred, which could be due to a systematic change in the process being studied or an external factor affecting the results.

This definition reinforces the importance of analyzing trends over time. A shift of this nature emphasizes that what was previously considered stable might no longer be true, prompting further investigation into causes and potential improvements. The emphasis on six or more points helps to reduce the likelihood of attributing normal random variation to significant changes in the process.

Other options do not adequately capture the concept of a shift. For instance, finding five or more consecutive points on the median does not indicate a clear change but could reflect random variability around the median. Two consecutive runs or three oscillating data points do not provide enough evidence of a sustained shift in the underlying data trend.