# Column: Technical Aids: Test on Quality Control Statistics and Concepts

ASQ: JQT: Tests on Quality Control Statistics and Concepts

 January 2001 Volume 33 · Issue 1 Contents Test on Quality Control Statistics and Concepts by Lloyd S. Nelson INTRODUCTION Nearly fifty years ago Swan and Hicks (1954) published a list of thirty multiple-choice questions designed to test the reader's knowledge of quality control statistics. On the assumption that few present-day practitioners have seen this article I have selected, and occasionally edited, twenty of the questions for those who would like to test their "IQ in QC." Answers are given in Table 1, but the question numbers have been randomized to make it difficult for peeking to pay off. If control charting shows that the number of nonconforming items in various lots is in control, we can conclude that The manufacturing process was in control The product was well mixed before dividing into lots Either a or b is true All lots should be accepted Probability paper can be used To inspect a distribution for normality For control charting To reduce the importance of extreme values None of the above If drawing tolerances and the natural tolerances of a process operating under the normal law are the same, then the control limits for X-bar will be The tolerance limits The tolerance limits times n The tolerance limits divided by n The tolerance limits divided by The sum of the deviations of a group of measures from their mean divided by the number of measures equals 2 Zero X-bar X-bar control charts to examine the variation between averages of samples can be drawn by plotting Subgroup totals Subgroup ranges Subgroup sigmas Subgroup size MIL-STD-105 is used for Establishing control limits Setting tolerances Accepting material Inspecting threads A.O.Q.L means Average outgoing quality level Average outgoing quality limit Average outside quality limit Anticipated optimum quality level The probability of drawing at random exactly one nonconforming unit in a sample of 5 from a lot of 50 containing 20 percent nonconforming is divided into A p chart is used when data consist of Variables Attributes Standard deviations Weights In setting up a control chart for a certain process, sigma is found to be 11 units. Repeated measurements of the same part, using the same technique on which the chart is based, show a standard error of measurement of 5 units. The best estimate of the true standard deviation of the process is nearest to 6 units 10 units 11 units 12 units The standard deviation of the Poisson distribution is given by None of these When A and B are distributed independently, A – B is equal to A + B A – B When measurements show a lack of statistical control, the standard error of the mean Is related to confidence limits Is a measure of process variability Is simple to compute Has no meaning If nothing is known concerning the pattern of variation of a set of numbers, we can calculate the standard deviation of the set of numbers and state that the sample mean ±3 times the calculated standard deviation will include at least 88.9 percent of the population 95 percent of the population 99.7 percent of the population 100 percent of the population A block has a height specification of 1.000" ±0.015". Three blocks are stacked to make anassembly. The difference in height between the largest and smallest of 100 such assemblies is nearest to 0.030" 0.060" 0.090" More information is needed before an answer can be given It is sometimes economical to permit a process that is being monitored by an X-bar, R chart to go out of control when Individual R's exceed R-bar Cost of inspection is high Six sigma is appreciably less than the difference between specification limits The X-bar control limits are inside the drawing tolerance limits A p-chart based on samples taken from each box of a large shipment of parts can be used to test The homogeneity of the shipment Whether or not the parts are produced under control Whether or not the parts are within specification None of the above As compared with a single point outside a 3 limit two points in succession between a 2 and a 3 limit on an X-bar control chart for means are A more significant indication of an assignable cause An equally significant indication of an assignable cause A less significant indication of an assignable cause Unimportant A cumulative frequency distribution is called An operating characteristic A histogram A frequency polygon An ogive A consumer's risk of 10% means that The probability that a sampling plan will reject "good" material is 10% The probability that a sampling plan will accept "poor" material is 10% The acceptable quality level of the lot is 10% The unacceptable quality level of the lot is 10%. TABLE 1. Answers Reference Swan, R. O. and Hicks, C. R. (1954). "What's Your IQ in QC". Industrial Quality Control Vol. X, No, 6, pp. 84-87.