Ch 6 - Statistical Quality Control Flashcards
common causes of variation
random causes that cannot be identified
assignable causes of variation
causes that can be identified and eliminated
mean (average)
a statistic that measures the central tendency of a set of data
range
the difference between the largest and smallest observations in a set of data
standard deviation
a statistic that measures the amount of data dispersion around the mean
out of control
the situation in which a plot of data falls outside preset control limits
variable
a product characteristic that can be measured and has a continuum of values (e.g., weight, height, or volume)
attribute
a product characteristic that has a discrete value & can be counted；can often be evaluated with a simple yes-or-no decision
x-bar chart
a control chart used to monitor changes in the mean value of a process
range (R) chart
a control chart that monitors changes in the dispersion or variability of a process
p-chart
a control chart that monitors the proportion of defects in a sample
c-chart
a control chart used to monitor the number of defects per unit
process capability
the ability of a production process to meet or exceed preset specifications
product specifications
preset ranges of acceptable quality characteristics
process capability index
an index used to measure process capability
Cp = 1: process variability just meets specifications
Cp < 1: process variability is outside the range of specification
Cp > 1: process variability is tighter than specifications and the process exceeds minimal capability
Six Sigma quality
a high level of quality associated with approximately 3. 4 defective parts per million
organized around a 5-step plan known as DMAIC: Define, Measure, Analyze, Improve, & Control
Sampling plan
a plan for acceptance sampling that precisely specifies the parameters of the sampling process and the acceptance/rejection criteria
single sampling - a random sample is drawn from every lot
double sampling - an opportunity to sample the lot a second time if the results of the first sample were inconclusive
multiple-sampling - similar to double sampling
operating characteristic (OC) curve
a graph that shows the probability or chance of accepting a lot given various proportions of defects in the lot
the steeper the curve, the better our sampling plan is for discriminating between “good” and “bad”
acceptable quality level (AQL)
the small percentage of defects that customers are willing to accept
lot tolerance percent defective (LTPD)
the upper limit of the percentage of defective items consumers are willing to tolerate
consumer’s risk
the chance of accepting a lot that contains a greater number of defects than the LTPD limit
producer’s risk
the chance that a lot containing an acceptable quality level will be rejected
average outgoing quality (AOQ)
the expected proportion of defective items that will be passed to the customer under the sampling plan
statistical quality control (SQC)
the general category of statistical tools used to evaluate organizational quality
