Guide to Control Charts

Question: 1. Describe the experience in the project. 2. What were the solutions used to address the problem? 3. Was the case you described a special-cause or common-cause? 4. Do you feel the solution or approach used appropriate for the cause? 5. What would you do if you could do it again? 6. What conclusions can you draw from the problem-solving or process-improvement techniques? Answer: Given, the company has collected The OTR time (time between placing the order and receipt of payment) data for various countries where it operates. Given below is the data of the OTR time and the country code for which the data was collected. Country Code Cycle Time Country Code Cycle Time 1 20 5 29 1 24 6 40 1 46 7 157 1 26 8 19 14 38 5 24 1 15 1 81 1 15 7 53 17 23 7 26 1 31 1 28 1 31 1 34 6 64 1 34 5 29 7 50 5 44 1 52 1 32 1 19 1 15 1 44 7 11 14 150 7 14 7 29 1 89 17 23 17 41 6 79 7 41 17 17 1 36 6 13 8 43 7 32 17 21 8 42 8 28 8 46 7 18 7 88 8 47 14 24 6 26 7 7 6 47 1 33 5 9 5 129 7 42 17 41 5 5 17 43 6 27 14 42 6 27 14 42 1 33 7 53 7 44 7 53 1 21 7 48 1 22 5 21 1 50 1 19 1. OTR time is defined as the time taken between placing an order and receiving its payment. For the 76 installations given below, the mean of installation time = Xi / n =38.93 and the standard deviation = 27.86. Thus it can be seen that the most of the data lies around the mean and is randomly distributed with no trend or pattern. Hence we can say that the data is stable. 2. To evaluate the stability of the OTR time, we will use X bar S chart. When the variable being measured is of continuous nature, we use x bar chart. Also since the sample size is different for all of the subgroups (country code) we use an S chart instead of R chart to evaluate the stability of the OTR time. (Martz, 2011) The UCL and LCL changes as the subgroup sizes are not equal. 3. The distribution of the cycle time is random and lies above and below the mean cycle time. The plot below gives idea about the distribution of cycle time. (Berardnelli, 2011) There are few points which are out of the control limits which make the data unstable. The data for the country code 7 and 14 have values which are out of the control limits and make the data unstable. 4. When we calculate the average cycle time for different Country codes, it can be seen that the average cycle time for the country code 17 is the least while the average cycle time of the country code 14 is the highest. Also the variation in the country code 14 is very high which makes the data very unstable. For all the other countries the variance is less and the data is randomly distributed and stable. Thus it can be said that the country code has an impact on the OTR time. Country Code Average Time 1 34.00 5 36.25 6 40.38 7 45.06 8 37.50 14 59.20 17 29.86 References Berardinelli, C. A. (2011).Guide to Control Charts. Retrieved on August 9, 2016 from https://www.isixsigma.com/tools-templates/control-charts/a-guide-to-control-charts/ Martz,E. (2011). Which Control Chart Should I Use? Retrieved on August 9, 2016 from https://blog.minitab.com/blog/understanding-statistics/what-control-chart-should-i-use