In which scenario is a Pareto chart most useful?

A Pareto chart is most useful in illustrating the frequency of different causes contributing to a particular problem, which aligns perfectly with the selected answer. This type of chart is built on the Pareto principle, or the 80/20 rule, which states that a small number of causes typically lead to a large portion of the effects. By using a Pareto chart, practitioners can visually identify and prioritize issues in order to address the most significant contributors first, ultimately directing their focus and resources efficiently to drive improvements.

In this context, the other options do not leverage the primary strength of a Pareto chart. Tracking changes over time is better suited to time series charts, which can plot data points chronologically to observe trends. Determining patient outcomes typically requires specialized metrics and analysis that go beyond simple frequency counts, as it demands a holistic view of clinical and operational data. Lastly, assessing process efficiency often involves a combination of different tools and metrics that measure workflow, resource utilization, and time management, rather than just the frequency of problems.