Checklists : Data collection throug

Checklists : Data collection through the use of a checklist is often the first step in the analysis of a metric. A checklist is a form used to record the frequency of occurrence of certain process failures. A process failure is any performance shortfall, such as error, delay, environmental waste, rework, and the like. The characteristics may be measurable on a continuous scale (e.g., weight, customer satisfaction on a 1 to 7 scale, unit cost, scrap loss percentage, time, or length) or on a yes-or-no basis (e.g., customer complaint, posting error, paint discoloration, or inattentive servers).Histograms and Bar Charts : Data from a checklist often can be presented succinctly and clearly with histograms or bar charts. A histogram summarizes data measured on a continuous scale, showing the frequency distribution of some process failure (in statistical terms, the central tendency and dispersion of the data). Often the mean of the data is indicated on the histogram. A bar chart (see Figure 2.11) is a series of bars representing the frequency of occurrence of data characteristics measured on a yes-or-no basis. The bar height indicates the number of times a particular process failure was observed.Pareto Charts : When managers discover several process problems that need to be addressed, they have to decide which should be attacked first. Vilfredo Pareto, a nineteenth-century Italian scientist whose statistical work focused on inequalities in data, proposed that most of an “activity” is caused by relatively few of its factors. In a restaurant quality problem, the activity could be customer complaints and the factor could be “discourteous server.” For a manufacturer, the activity could be product defects and the factor could be “missing part.” Pareto’s concept, called the 80–20 rule, is that 80 percent of the activity is caused by 20 percent of the factors. By concentrating on the 20 percent of the factors (the “vital few”), managers can attack 80 percent of the process failure problems. Of course, the exact percentages vary with each situation, but inevitably relatively few factors cause most of the performance shortfalls. The few vital factors can be identified with a Pareto chart, a bar chart on which the factors are plotted along the horizontal axis in decreasing order of frequency (see Figure 2.12). The chart has two vertical axes, the one on the left showing frequency (as in a histogram) and the one on the right showing the cumulative percentage of frequency. The cumulative frequency curve identifies the few vital factors that warrant immediate managerial attention.