Stats 1
According to the Empirical Rule, 95% of the area under the normal curve is within two standard deviations of the mean. What percent of the area under the normal curve is more than two standard deviations from the mean?
5%
Which of the following would compute a CRITICAL VALUE for a 96% level of confidence to estimate the population mean when sigma is known and the sample size is 25.
=NORMSINV(0.02)
Which of the following formulas would you use to compute a critical value for a 90% level of confidence to estimate the population mean given an assumed standard deviation of 10 and a sample size of 35,
=NORMSINV(0.95)
Which of the following formulas would you use to compute a critical value for a 90% level of confidence to estimate the population mean given a sample standard deviation of 10 and a sample size of 35,
=T.INV.2T(0.10,34)
Which of the following is a correct explanation of what a confidence interval is?
a range of values used to estimate the true value of a population parameter.
Assuming a normal distribution, as the standard deviation increases, the shape of curve:
becomes shorter and wider.
All else equal, an increase in sample size will cause a(n)
decrease in the size of a confidence interval.
Which of the following would increase the width of a confidence interval for a population mean?
Increase the level of confidence
Which is greater in a normal distribution, the mean or the median? Explain.
Neither; the mean and median are always equal in a normal distribution, since it is symmetric.
Days before a presidential election, a nationwide random sample of registered voters was taken. Based on this random sample, it was reported that "52% of registered voters plan on voting for Robert Smith with a margin of error of plus or minus3%." The margin of error was based on a 95% confidence level. Can we say with 95% confidence that Robert Smith will win the election if he needs a simple majority of votes to win?
No, because 50% is within the bounds of the confidence interval.
Why does sample size need to be accounted for in the t-distribution?
The t-distribution changes for different sample sizes.
Health-care workers who use latex gloves with glove powder on a daily basis are particularly susceptible to developing a latex allergy. Each worker in a sample of 30 hospital employees who were diagnosed with a latex allergy was asked how many latex gloves they used per week. A 99% confidence interval was (17 gloves/week, 25 gloves/week). What would happen if a sample of 40 employees was taken instead?
The width of the confidence interval would decrease.
What would happen to the width of a confidence interval if the level of confidence increased (assuming everything else remained the same)?
The width of the confidence interval would increase.
If a z-score is equal to zero, which of the following must be true?
The x-value must be equal to the mean of the distribution.
The possible values that we believe a population mean will be with a certain level of confidence
form a confidence interval for the population mean.
All else equal, an increase in the level of confidence will cause a(n)
increase in the size of a confidence interval.
Days before a presidential election, an article based on a nationwide random sample of registered voters reported the following statistic, "52% (plus or minus3%) of registered voters will vote for Robert Smith." What is the "plus or minus3%" called?
margin of error
As the standard deviation of a normal curve decreases, the data becomes __________ centered around the mean.
more
The larger the sample, the __________ accurate the sample mean will be as an estimate of the population mean.
more
A critical value is _____________.
the number of standard errors (or standard deviations) to move from the mean of a sampling distribution to correspond to a specified level of confidence.
When sampling and the standard deviation is not known, what is used to estimate it?
the standard deviation of the data from the sample
