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What is the status of for zbased confidence intervals for a population mean?
is known

What is the status of for tbased confidence intervals for population mean?
is unknown

What two things does Statistical Inference involve?

What do we use statistical inferences for?
To make inferences about a parameter

What are the two types of estimates of parameters?
 Point estimate
 Interval estimate

What is a Interval Estimate?
It's a point estimate with a +/ Margin of Error

What is the purpose of an Interval Estimate?
Provide info about how close the point estimate is to the parameter

In an Interval Estimate, what does the Width depend on?
How much confidence you want in your estimate

What is Precision?
Width of an interval

What is Accuracy?
Probability of the estimate being correct, defined as

What is the general form of the interval estimate for the population mean?
+/ Margin of Error

What is the interval estimate of equation if is known?

What is ?
The confidence coefficient

What is ?
The zvalue that provides an area of in the upper tail of the standard normal prob distribution

Assume:
Population of all individual car mileages is ND
Standard deviation ( ) is 0.8
A sample size (n) of 50
Build a 95% interval estimate of
 We have 95% confidence that will be within +/ .22 mpg of the population mean
 (from ztable)
 Margin of error = (1.96)(.113) = .22

If we have 95% confidence that will be within +/ .22 mpg of the population mean...
Assume = 31.56
What is the confidence interval?
[31.56 +/ 0.22] = [31.34, 31.78]

If = 0.10 (90% confidence) what is the confidence interval width?
1.645

If = 0.05 (95% confidence) what is the confidence interval width?
1.96

If = 0.01 (99% confidence) what is the confidence interval width?
2.576

What probability of values is between zscores of 1.645 and +1.645?
0.9000

What probability of values is between zscores of 1.96 and +1.96?
0.9500

What probability of values is between zscores of 2.576 and +2.576?
0.9900

What is used instead of when it is not known?
 s
 Sample standard deviation

What is the tscore standard error equation?

What is the tscore equation?

What are the differences between the tdistribution and the zdistribution?
 tdistribution is more spread out than the standard normal (zdistribution)
 tdistribution is defined by the # of degrees of freedom (df = n  1)

What happens to the degrees of freedom (df) as n (sample size) increases?
df increases

What happens to the tcurve as the degrees of freedom (df) increases?
 tcurve narrows
 Spread decreases
 Eventually approaches the standard normal curve

At what sample size does the tcurve become very similar to the zcurve?

At what sample size is the zdistribution used INSTEAD of the tdistribution?

What's the differences between the ttable and the ztable?
 ttable shows values to the RIGHT of the tscore
 ttable is based on df and not n

What is the Confidence Interval equation for the tdistribution ( is not known)?

In a sample of 16 management consultants, the following statistics about hourly wages have been computed:
Construct a 95% confidence interval (C.I.) estimate.

