Having already had a statistics course use your knowledge

Question

Controlling Process Problem

The two major pottery producers in North Africa are located in Morocco and Algeria. The Kabylie Company in Algiers has been making a specific style of jar that has been very popular in France for over 200 years. The clay used in the pots ranges from 15.2 to 15.8 ounces. There is a problem if the clay weighs less than 15.2 or more than 15.8 ounces so maintaining quality control is critical. The company has two shifts that measure the weights of the clay that goes into each jar. Although there are scales to measure the proper weight some workers just "eyeball" the amount of clay which may be out of specification. Recently some of the jars have been not met specifications and distributors have been complaining and threatening to find new producers.

Shift 1
Obs	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15
1	15.18	15.55	15.37	15.24	15.37	15.58	15.46	15.49	15.55	15.58	15.52	15.34	15.55	15.37	15.68
2	15.58	15.62	15.37	15.49	15.49	15.46	15.58	15.52	15.65	15.18	15.31	15.34	15.34	15.40	15.40
3	15.49	15.49	15.24	15.65	15.58	15.43	15.52	15.34	15.49	15.34	15.49	15.68	15.49	15.28	15.49
4	15.58	15.83	15.52	15.58	15.43	15.46	15.55	15.52	15.52	15.52	15.49	15.55	15.43	15.52	15.49
5	15.55	15.31	15.43	15.52	15.49	15.43	15.52	15.46	15.58	15.52	15.37	15.31	15.52	15.49	15.58
6	15.24	15.55	15.49	15.55	15.55	15.52	15.46	15.43	15.49	15.31	15.43	15.46	15.55	15.62	15.74
7	15.62	15.58	15.43	15.55	15.49	15.46	15.68	15.37	15.52	15.43	15.52	15.40	15.46	15.43	15.40
8	15.24	15.49	15.49	15.37	15.52	15.52	15.65	15.49	15.40	15.43	15.40	15.40	15.65	15.74	15.43
9	15.34	15.34	15.31	15.55	15.34	15.43	15.40	15.31	15.71	15.49	15.49	15.37	15.55	15.31	15.49
10	15.55	15.46	15.74	15.31	15.49	15.34	15.62	15.43	15.55	15.52	15.43	15.55	15.68	15.55	15.40
average	15.44	15.22	15.44	15.48	15.48	15.46	15.54	15.44	15.55	15.43	15.45	15.44	15.52	15.47	15.51
Shift 2
1	15.58	15.55	15.46	15.37	15.58	15.55	15.74	15.80	15.99	15.49	15.40	15.83	15.83	15.18	15.55
2	15.18	15.34	15.40	15.40	15.43	15.58	15.40	15.28	15.24	15.40	15.21	15.65	15.43	15.24	15.43
3	15.55	15.31	15.62	15.43	15.49	15.43	15.28	15.24	15.46	15.74	15.96	15.28	15.89	15.40	15.06
4	15.43	15.65	15.55	15.49	15.40	15.68	15.00	15.28	15.49	15.71	15.37	15.96	15.96	15.24	15.31
5	15.52	15.34	15.55	15.55	15.43	15.62	15.71	15.58	15.43	15.31	15.21	15.43	15.80	15.62	15.28
6	15.46	15.46	15.46	15.58	15.49	15.62	15.34	15.37	15.46	15.37	15.71	15.12	15.86	15.58	15.40
7	15.46	15.40	15.49	15.43	15.46	15.46	15.28	15.06	15.52	15.89	15.96	14.69	15.52	15.21	15.65
8	15.55	15.49	15.49	15.37	15.43	15.43	15.46	15.74	15.71	15.28	15.34	15.18	15.28	15.34	15.40
9	15.52	15.49	15.65	15.55	15.58	15.40	14.93	15.37	15.28	15.37	15.21	15.58	15.62	15.43	15.58
10	15.40	15.46	15.34	15.58	15.49	15.46	15.65	15.93	15.58	15.21	15.83	15.62	15.58	15.74	15.24
average	15.47	15.45	15.50	15.48	15.48	15.52	15.38	15.46	15.52	15.48	15.52	15.43	15.68	15.40	15.39

The manager thinks the second shift is the problem. He purposefully took the first half of the samples from lower production in each shift and the second half of the samples from full production in each shift. He took 15 random samples from each shift and did not seem to notice any significant differences between shifts.

Having already had a statistics course use your knowledge of statistical quality control to determine how to find the problem and when it began.