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27 Cards in this Set

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Robust means that:
When the confidence level or P-value does not change very much even when the conditions are not met.
To be Robust, what are the conditions?
No outlier, no extreme skewness.
a= ?
a= symbol for level of significance
Purpose of confidence interval is to estimate the:
a. Population mean
b. Sample mean
a. Population mean
True mean is also known as:
Population mean
If asked what is the appropriate formula for a confidence interval for mu what do we look for?
1. If the population size is < 30 we use t* , if >30 we use z*
2. When population st dev is not given - use t*

(First determine: Population size? Second: is population stdev given?)
You can only use t* distribution when the distribution is:
normal
When n=less < 30 make sure ther are no:
outliers or skewedness
If asked "What would be checked in order to validly use given formula when n=15" ....what do we look for?
Make sure there is no outliers or strong skewedness in a plot of the data. (when n=<30)
If the sample size is the same and a= same and o= same for both groups then the margin of error are:
the same
When n increases, the margin of error:
decreases
When CONFIDENCE LEVEL increases, the margin of error:
Also increases
Can you recommend using a one-sample t confidence interval estimate for mu if there is an outlier in the data?
No, t distribution is not appropriate in this case since there is an outlier.
Rule for using confidence interval of the difference between two means:

(Reject, Fail to Reject?)
Reject Ho if the confidence interval does NOT contain zero.

Fail to reject Ho if the confidence interval does contain zero.
Reject Ho if the confidence interval:
does NOT contain zero
Fail to reject Ho if the confidence interval:
does contain zero.
If asked to conclude that there is a significant difference aka reject/fail to reject Ho, you must look for what words in the problem?
1. For the difference
2. Look at the mean intervals (does it contain a zero?)
3. significant difference
If asked if we can conclude the mean variable differs from a given data variable what do we look for?

Sample Question: You want to compare the daily items sold for two game consoles: Playstation3(PS3) and NintendoWII(WII). Over the next 80 days, 40 days are randomly assigned to PS3 and 40 days to WII. At the end, you compute a 95% confidence interval for the difference in mean daily items sold for the two game consoles to be (-20, -10). On the basis of this confidence interval, can you conclude that there is a significant difference between the mean daily items sold for the two game consoles at α=0.05? (i.e., can you reject Ho?)
Look between the confidence interval (2.84,3.06) and determine if the given data variable (3.1) would show up between the two confidence interval data points
Margin of error questions use the n=z*o/m^2 formula...when you finish you always round:
up
Which of the following questions does a test of significance answer?
Is the observed effect too large to be due to chance alone?
Which one of the following statements best describes the logic of tests of significance?
An outcome that would rarely happen if Ho were true is good evidence that Ho is not true.
Type I error and Type II errors are:
Type I - when a true null hypothesis is rejected
Type II - when a false null hypothesis is not rejected (fail to reject Ho when Ho is false)
Increasing the sample size increases the _____ of the test.
power
The P-value for a significance test is defined as
the probability of obtaining a test statistic that has a value at least as extreme as that actually observed, assuming the null hypothesis is true.
Small P-value means that there is stronger evidence AGAINST the
Null Hypothesis
Large P-value SUPPORTS the
Null Hypothesis
What does the normal curve represent if a one-sided test on Mu with o known, and the p-value represented as the area in the tail of the normal curve.
All possible values of and how often they occur if Ho were true.