7QC Tools — Histogram of Discrete DataAmrendra Roy
Histogram is a pictorial view of the data set, it is like a portrait of your data. It tells you how your data looks like, where your most of the data is clustered (whether it is the mean or median is the true measure of the central tendency). In short it tells you about the distribution of the data set.
Histogram divides the data set into small sub-units, called as “classes”. This is followed by arranging data according to the class it belongs. In this way we have “class-range” along with their frequencies (i.e. how many data points are there in that class). This is followed by plotting a bar-graph of class Vs frequency, which is known as histogram.
In the check list example we have collected the data about the Reason for failure (= class) and number of defects because of that reason (= frequency).
Now, if we plot the bar graph of the above data, we will get a histogram as shown below, it appears that defects due to reason C, D and G is more prominent and these three requires immediate attention.
The above data set is a discrete variable hence, the bars of the histogram are not touching each other.
Kindly do provide feedback for continuous improvement