Tracking Users Complaints using Statistical Quality Control: Control Chart

Welcome to the new post as part 2 in our series on mechanisms to include statistics within Oracle Business Intelligence (first part see previouspost).

A control chart is a graph used to monitor quality and in this article we focus on monitoring the number of complaints per month. So, using Oracle Business Intelligence, after setting the Preferences for the chart, we can observe that the results are such as:

In our case, a process is in control when the number of complaints per month  are subject only to common cause variation (such as environment, methods,...). Anyway, a proces is out of control  when data points fall outside of the control limits, that means that the process are subject to variation because of assignable causes of variation.

Background: Using control charts can be measured: variables (continuous of values)  and attibutes (discretes values). Our case, number of complaints per month are considered as attributes, where the average number of number of complaints per month, c̄, is the Center line (within the Control Chart), and then let’s obtain the Upper and Lower Control Limits as it’s shown below:

If the process is in control, data points (in our case number of complaints/month) will fall inside 3-sigma limits  99,73% of the time (within control limits). Moreover, each data point(in our case number of complaints/month)  is a Hypothesis test, so:

Ho: μ = c̄

Ha: μ ≠ c̄

α = 0,0027

We reject Ho cases outsite the limits.

Hope it helps!

Best wishes.

Joan Martí.