STAT 121 Exam Prep Questions Verified Answers
how to find probability of an individual (x) in a normal shaped population
use Z=(X-mu)/sigma and the normal table
how to find probability of an individual (x) in a non-normal shaped population
nothing we can do
how to find probability of a sample mean (x-bar) in a normal shaped population
use Z=(x-bar - mu)/(sigma/sqrtn) and the normal table
how to find probability of a sample mean (x-bar) in a non-normal shaped population with
n>30
CLT!!! use Z=(x-bar - mu)/(sigma/sqrtn) and the normal table
how to find probability of a sample mean (x-bar) in a non-normal shaped population with
n<30
nothing we can do
clues that we are looking for sample means in a probability calculation problem
will be given a sample size; see "mean", "sample", or "x-bar"
process
sequence of operations or a series of interconnected steps in producing a product or service
2 types of variation in all processes
natural/chance or unnatural
, role of Statistical Process Control
SPC identifies, measures, and monitors both types of variation using a control chart to
distinguish between natural/ordinary variation and unnatural variation due to a problem
process in statistical control
one whose inputs and outputs exhibit natural variation over time (typically 3SD above or
below mu/pop mean)
signals of an out of control process
1 point above or below control limits (3SD above or below)
OR
run of 9 points in a row on same side of centerline
what is the centerline of a control chart?
mu
what is the upper control limit of a control chart?
mu + 3(sigma/sqrtn)
what is the lower control limit of a control chart?
mu - 3(sigma/sqrtn)
Statistical Dogma for Processes
all processes have natural variation and are occasionally susceptible to unnatural variation
what do you do if SPC finds unnatural variation?
stop process, find cause of unnatural variation, fix problem, resume process
x-bar control chart
statistical tool for monitoring a process that has variation, altering us when a problem
or UNNATURAL variation has occurred
how to find probability of an individual (x) in a normal shaped population
use Z=(X-mu)/sigma and the normal table
how to find probability of an individual (x) in a non-normal shaped population
nothing we can do
how to find probability of a sample mean (x-bar) in a normal shaped population
use Z=(x-bar - mu)/(sigma/sqrtn) and the normal table
how to find probability of a sample mean (x-bar) in a non-normal shaped population with
n>30
CLT!!! use Z=(x-bar - mu)/(sigma/sqrtn) and the normal table
how to find probability of a sample mean (x-bar) in a non-normal shaped population with
n<30
nothing we can do
clues that we are looking for sample means in a probability calculation problem
will be given a sample size; see "mean", "sample", or "x-bar"
process
sequence of operations or a series of interconnected steps in producing a product or service
2 types of variation in all processes
natural/chance or unnatural
, role of Statistical Process Control
SPC identifies, measures, and monitors both types of variation using a control chart to
distinguish between natural/ordinary variation and unnatural variation due to a problem
process in statistical control
one whose inputs and outputs exhibit natural variation over time (typically 3SD above or
below mu/pop mean)
signals of an out of control process
1 point above or below control limits (3SD above or below)
OR
run of 9 points in a row on same side of centerline
what is the centerline of a control chart?
mu
what is the upper control limit of a control chart?
mu + 3(sigma/sqrtn)
what is the lower control limit of a control chart?
mu - 3(sigma/sqrtn)
Statistical Dogma for Processes
all processes have natural variation and are occasionally susceptible to unnatural variation
what do you do if SPC finds unnatural variation?
stop process, find cause of unnatural variation, fix problem, resume process
x-bar control chart
statistical tool for monitoring a process that has variation, altering us when a problem
or UNNATURAL variation has occurred
