Histogram and Pareto Charts

Histograms

Histograms look very much like column charts but are very different. Column charts show volume. Histograms show frequencies.

Histograms are often used to visualize central tendency. They are easy to understand and can tell you a lot about your data. The steps include grouping the data into ‘Bins’ and plotting the number of occurrences within that bin.

In the image, we have a new bin for each 1% starting at 21% increasing to 27%. The values are placed in the bins and the count of each bin is charted. For example, in the data shown the bin for 23% has 5 values. The height of the bars in a column chart represents the frequency or count. Whereas the labels represent the bins.

If the histogram is symmetrical, i.e. cut it in half and each half be the mirror image of the other we can assume they mean to be the closest approximation of the center.

If the histogram is not symmetrical then the median should be used to approximate the center.

If the data is left-skewed on the histogram (thinner tail on the left side), then the mean is LESS THAN the median. This is known as negatively skewed.

If the data are right-skewed on the histogram (thinner tail on the right), then the mean is GREATER THAN the median. This is known as positively skewed.

Pareto Chart

A Pareto chart is just like a histogram except the bins are organized from highest frequency to lowest. A Pareto chart also contains a line. This line shows the total cumulative frequency. It represents the Pareto philosophy which also known as the 80/20 rule. It does so by displaying events by order of impact.

A histogram may be used to represent the number of students who scored between a certain score range, such as 0 to 20%, 20 to 40%, etc.

A Pareto chart may be used to analyze the causes of customer dissatisfaction. The causes would be ordered by frequency of occurring, allowing the team to focus on those issues with the biggest impact on customer satisfaction.