On November 1, 2013 John Adams, a customer servicerepresentative of Americo Drilling Supplies (ADS), was summoned tothe Houston office of Drilling Contractors, Inc. (DCI), to inspectthree boxcars of mud-treating agents that ADS had shipped to theHouston firm. DCI had filed a complaint that the 25 Pound bags oftreating agents that it had just received from ADS werelight-weighted.

The light-weight bags were initially detected by one of DCI’sreceiving clerks, who noticed that the rail road side scale ticketsindicated that the net weights were significantly less on all threeof the boxcars than those of identical shipments received onOctober 25, 2013. ADS’s traffic department was called to determineif lighter-weight dunnage or pallets were used on the shipments.(This might explain the lighter weights.) ADS indicated, however,that no changes had been made in the loading or palletizingprocedures. Hence, DCI randomly checked 25 of the bags anddiscovered that the average net weight was almost 24.5 pounds.Consequently, they concluded that the sample indicated asignificance short-weight. ADS, was then contacted, and Adams wassent to investigate the complaint and to issue credit (???) toDCI.

DCI, however, was not completely satisfied with only theissuance of credit for the short shipment. The charts followed bytheir mud engineers on the drilling platforms were based on25-pound bags of treating agents. Lighter-weight bags might resultin poor chemical control during the drilling operation and mightadversely affect drilling efficiency. (Mud-treating agents are usedto control the pH and other chemical properties of the open duringdrilling operations.) This could cause severe economic consequencesbecause of the extremely high cost of oil and natural gas drillingoperations. Consequently, special use instructions had to accompanythe delivery of these shipments to the drilling platforms.Moreover, the light-weight shipments had to be isolated in DCIwarehouse, causing extra handling and poor space utilization.Hence, Adams was informed that CDI might seek a new supplier ofmud-treating agents if in the future it received bags that deviatedsignificantly below 25 pounds.

The quality control department at ADS suspected that thelight-weight bags may have resulted from “growing pains” at theOrange, Texas plant. Because of the earlier energy crises, oil andnatural gas exploration activity had greatly increased. Thisincreased activity, in turn, created increased demand for productsproduced by related industries, including drilling muds.Consequently, ADS had to expand from one shift (6 A.M. to 2 P.M.)to a two-shift (2 P.M. to 10 P.M.) operation in Mid 2011s, andfinally to a three-shift operation (24 hours per day) in January of2013.

The additional night shift bagging crew was staffed entirely bynew employees. The most experienced foremen were temporarilyassigned to supervise the night shift. Most emphasis was placed onincreasing the output of bags to meet the ever-increasing demand.It was suspected that only occasional reminders were made todouble-check the bag weight feeder. (A double check is performed bysystematically weighting a bag on a scale to determine if theproper weight is being loaded by the weight-feeder. If there issignificant deviation from 25 pounds, corrective adjustments aremade to the weight-release mechanism.)

To verify this expectation, the quantity control staff at ADSrandomly sampled the bag output and prepared the following table(see Excel dataset). Ten bagswere sampled and weighted each hour.  

e. Is there any differences between performances ofthree shifts? Hint: (Carve out the morning, afternoon, and nightshift data into three columns and graph their averages. Explainyour findings based on graph.

Sample# Time Average(X-bar) Smallest Largest Range 1 6:00 AM 25.2 24.9 25.7 2 7 25.4 25.3 26.2 3 8 25.2 25.1 26.4 4 9 25.5 25.2 26.1 5 10 25.1 25.2 26.3 6 11 25.5 24.9 25.7 7 12 Noon 25.1 24.8 25.3 8 1:00 PM 25 24.5 25.4 9 2 24.7 23.9 25.1 10 3 25.1 23.9 25.2 11 4 24.5 24.2 25.3 12 5 24.7 24.9 25.3 13 6 24.8 24.2 25 14 7 24.4 24 25 15 8 25 23.6 25.2 16 9 24.8 24.4 25.4 17 10 23.9 24.9 25.3 18 11 24.1 23.9 25.1 19 12 Mid Night 23.9 23.1 25.2 20 1:00 AM 23.7 22.6 24.7 21 2 23.8 22.7 24.6 22 3 23.9 22.8 24 23 4 23.5 22.5 24.1 24 5 24.1 22.1 24.6 25 6 25 24.6 25.1 26 7 25.2 24.2 26.1 27 8 25 24 25.5 28 9 25 24.4 26.7 29 10 25.1 24.6 26.8 30 11 25.2 24 26.3 31 12 Noon 25.2 23.8 26.4 32 1:00 PM 25.3 24.4 26.1 33 2 24.9 23.6 26 34 3 24.6 23.8 26.7 35 4 24.4 23.7 25.9 36 5 24.7 23.9 25.1 37 6 24.5 23.2 26.2 38 7 24.6 24.1 26.7 39 8 24.2 23.2 24.9 40 9 24.4 24.2 25.1 41 10 24.1 23.6 25.2 42 11 23.8 23.1 25 43 12 Midnight 24.1 23.2 25.4 44 1:00 AM 23.8 23.4 26.7 45 2 23.6 23 25.2 46 3 24.5 23.4 25 47 4 23.4 22.7 23.8 48 5 23.7 22.9 24.5 49 6 25.1 23.8 25.4 50 7 24.8 23.4 25.6 51 8 24.8 23 26.8 52 9 25.2 24.1 25.7 53 10 25.2 24.8 25.4 54 11 25.4 24.5 25.7 55 12 Noon 25.2 23.7 25.9 56 1PM 24.9 23.7 26.2 57 2 24.6 23.4 26 58 3 24.7 23.8 25.8 59 4 24.8 24.1 25.6 60 5 24.3 23.9 26.2 61 6 24.6 22.8 24.7 62 7 24.6 23.7 25 63 8 24.4 22.9 24.8 64 9 24.6 22.2 24.9 65 10 24.4 23.1 25.1 66 11 23.9 22 25.2 67 12 Midnight 23.5 22.1 24.2 68 1:00 AM 23.4 22.3 24 69 2 24 23.8 25 70 3 23.8 23.1 24.6 71 4 23.9 23.2 24.5 72 5 23.5 22.3 25.1