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Gravity
Terms in this set (64)
some degree of variability is present in almost all processes
true
the purpose of process control is to detect when natural causes of variation are present
false
a normal distribution is generally described by its two parameters: the mean and the range
false
a process is said to be in statistical control when assignable causes are the only sources of variation
false
mistakes stemming from workers' inadequate training represent an assignable cause of variation
true
averages of small samples, not individual measurements, are generally used in statistical process control
true
the x bar chart indicates that a gain or loss of uniformity has occurred in dispersion of a production process
false
the central limit theorem states that when the sample size increases, the distribution of the sample means will approach the normal distribution
true
in statistical process control, the range often substitutes for the standard deviation
true
if the process average is in control, then the process range must also be in control
false
a process range chart illustrates the amount of variation within the samples
true
mean charts and range charts complement one another, one detecting shifts in process average, the other detecting shifts in process dispersion
true
x bar charts are used when we are sampling attributes
false
to measure the voltage of batteries, one would sample by attributes
false
a p chart is appropriate to plot the number of typographic errors per page of text
false
a c-chart is appropriate to plot the number of flaws in a bolt of fabric
true
the x bar chart, like the c chart, is based on the exponential distribution
false
a process that is in statistical control will always yield products that meet their design specifications
false
the higher the process capability ratio, the greater the likelihood that process will be within design specifications
true
the Cpk index measures the difference between desired and actual dimensions of goods or services produced
true
acceptance sampling accepts or rejects an entire lot based on the information contained in the sample
true
a lot that is accepted by acceptance sampling is free of defects
false
in acceptance sampling, a manager can reach the wrong conclusion if the sample is not representative of the population it was drawn from
true
the probability of rejecting a good lot is known as consumer's risk
false
an acceptance sampling plan must define good lots and bad lots and specify the risk level associated with each one
true
the acceptable quality level is the average level of quality we are willing to accept
false
the steeper an OC curve, the better it discriminates between good and bad lots
true
if a sample of items is taken and the mean of the sample is outside the control limits the process is
out of control and the cause should be established
the causes of variation in statistical process control are
natural causes and assignable causes
natural variations
lead to occasional false findings that processes are out of control
assignable variation
is to be identified and eliminated
assignable causes
are causes of variation that can be identified and removed
control charts for variables are based on data that come from
averages of small samples
the purpose of an x chart is to determine whether there has been a
change in the central tendency of the process output
statistical process control charts
display upper and lower limits for process variables or attributes, and signal when a process is no longer in control
a sample of parts is measured. the mean of this sample is in the middle of the control limits, but some individual parts measure too low for design specifications and other parts measure too high. Which of the following is true?
the process is in control, but not capable of producing within the established control limits
The Central Limit Theorem
allows managers to use the normal distribution as the basis for building some control charts
up to three standard deviations above or below the centerline is the amount of variation that statistical process control allows for
natural variation
A manager wants to build 3 standard deviation control limits for a process. the target value for the mean of the process is 10 units and the standard deviation of the process is 6. if samples of size 9 are to be taken the UCL and LCL will be
16 and 4
the type of inspection that classifies items as being either good or defective is
attribute inspection
the x bar chart tells us whether there has been a
change in the central tendency of the process output
jars of pickles are sampled and weighed. sample measures are plotted on control charts. the ideal weight should be precisely 11 oz. which type of charts would you recommend?
x and r charts
the usual purpose of an r chart is to signal whether there has been a
gain or loss in dispersion
plots of sample ranges indicate that the most recent value is below the lower control limit. what course of action would you recommend?
variation is not in control; investigate what created this condition
to set x chart upper and lower control limits, one must know the process central line, which is the
average of the sample means
according to the text, the most common choice of limits for control charts is usually
+/- 3 standard deviations
which of the following is true of a p chart?
the lower control limit may be at zero
the normal application of a p chart is in
process sampling by attributes
the statistical process chart used to control the number of defects per unit of output is the
c chart
the c chart signals whether there has been a
change in the number of defects per unit
a manufacturer uses statistical process control to control the quality of the firm's products. samples of 50 of product a are taken, and a defective acceptable decision is made on each unit sampled. For product b, the number of flaws per unit is counted. what types of control charts should be used?
p chart for A, c chart for B
a nationwide parcel delivery service keeps track of the number of late deliveries per day. they plan on using a control chart to plot their results. Which type of control charts would you recommend?
c-charts
which of the following is true regarding the process capability index?
the larger the Cpk, the more units meet specifications
if the Cpk index exceeds
Standard deviation must be less than one third of the difference between the specification and the process mean
the statistical definition of six sigma allows for 3.4 defects pre million. this is achieved by a Cpk index of
2
acceptance sampling's primary purpose is to
decide if a lot meets predetermined standards
an acceptance sampling plan's ability to discriminate between low quality lots and high quality lots is described by
an operating characteristics curve
acceptance sampling is usually used to control
incoming lots of purchased products
an operating characteristic curve describes
how well an acceptance sampling plan discriminates between good and bad lots
an operating characteristics curve shows
how the probability of accepting a lot varies with the population percent defective
producer's risk is the probability of
rejecting a good lot
which of the following is true regarding the relationship between AOQ and the true population percent defective?
AOQ is less than the true percent defective
Average outgoing quality usually
improves with inspection
a type I error occurs when
a good lot is rejected
;