ABSTRACT
Example 1.2 Nicoprone is manufactured by a batch production process. The plant manager is worried about the percentage impurity, which appears to be higher in recent batches than it was in batches produced some months ago. He suspects that the impurity of the final product may depend on the presence of polystyline in the resin which is one of the raw materials of the process. The supplier of the resin has agreed that the polystyline content will not exceed 1% on average and that no single bag will contain more than 2 .5%. Approximately 900 bags of resin are in the warehouse at the present time. The warehouse manager takes a sample of 18 bags by selecting every 50th bag on the shelf. From each of the selected bags a 20 gram sample* of resin is taken. The determinations of polystyline content are:
1.6% 0.5% 3 . 1 % 0.7% 0.8% 1.7% 1.4% 0.8% 1.1% 0.9% 2.4% 0.6% 2.2% 2.9% 0 .3% 0.5% 1.0% 1.3%
What is statistics? 3 We can easily calculate that the average polystyline content is equal to 1.32% and we notice that two of the determinations exceed 2 .5%. So the sample average is certainly greater than the specified limit of 1.0%, but we need to consider what this average might have been if the warehouse manager had selected a different sample of bags, or perhaps we should ask ourselves what the average polystyline content would have been if he had sampled all the bags in the warehouse.
