Confidence Intervals

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Questions

• What does a 95% confidence interval versus a 99% confidence interval tell you?
• Why is a 90% confidence interval narrower than a 95% confidence interval?
• What happens to the confidence interval if you increase the confidence level?
• If a data set of n=115 has a mean of 9.74 and a population standard deviation of 2.93, what is the 95% confidence interval?
• How do confidence intervals change with standard deviations?
• What does the confidence interval of a sample tell you?
• How do confidence intervals change with sample size?
• What is the difference between the confidence interval and margin of error?
• How does confidence interval change with sample size?
• What does a 95% versus a 99% confidence interval mean for a given estimate?
• The Harris Poll asked a sample of 1009 adults which causes of death they thought would become more common in the future. Gun violence topped the list: 706 members of the sample thought deaths from guns would increase. ?
• If I know the population mean but want to determine the standard deviation for a trail of several events; should I be dividing by the number of events or the number of events minus 1?
• If there is inflation in a country, what happens to its currency?
• Question #f9b61
• A group of 62 randomly selected students have a mean score of 28.3 on a standardized placement test. The population SD for all students taking the test is #sigma = 3.4#. What is the 90 percent confidence interval for the mean score?
• Question #eca69
• Question #0d541
• How do I rewrite the confidence interval (0.0268, 0.133) in the form of #hatp - E < p < hatp + E#?
• Five students were asked how many months had passed since their last visit to a dentist. They said 6, 16, 12, 22, 29. How do you construct a 95% confidence interval for the mean number of months elapsed since their last visit?
• What are confidence intervals?
• What critical value would you use for a 95% confidence interval based on the t(21) distribution?
• How do you construct a 90% confidence interval for the population mean, #mu#?
• A random sample of 90 observations produced a mean x̄ = 25.9 and a standard deviation s = 2.7. How do you find a 95% confidence interval for the population mean μ?
• What is meant by a 95% confidence interval?
• How do you interpret a 95% confidence interval?
• How do you find the 95% confidence interval?
• How do you find a 95% confidence interval for μ when n = 32, x-bar = 137 ft., and σ = 7.0 ft?
• How do you find the margin of error with a 90% confidence level, n = 200, sd = 2500, and mean = 9500?
• How do you find the margin of error for the 95% confidence interval used to estimate the following population proportion?
• How do you find the margin of error for the 95% confidence interval used to estimate the following population proportion: "In a clinical test with 2440 subjects, 70% showed improvement from the treatment."?
• How do you find the margin of error with n = 163, x = 96, and a 95% confidence interval?
• In a survey of 280 adults over 50, 75% said they were taking vitamin supplements. How do you find the margin of error for this survey if we want a 99% confidence in our estimate of the percent of adults over 50 who take vitamin supplements?
• A college counselor wants to determine the average amount of time freshmen spend studying. He samples 61 freshmen. The mean of the resulting scores is 20 hours, the standard deviation is 6.5 hours. What is the point estimate and the margin of error?
• How do you find the margin error for a 90% confidence level with n = 480, x = 130?
• How do you interpret confidence intervals in statistics?
• What is 'z' for an 88% confidence interval?
• In regards to confidence interval, what do we do if the variance is zero and our sample size is 15?
• How do you calculate a 95% confidence interval without the mean?
• What role do confidence intervals play in politics?
• What is a 90% confidence interval for the population mean birth weight based on the data?
• How do I construct a 95% confidence interval for the average amount spent on lunch by all customers?
• Will a 95% confidence interval typically contain nearly all of the observations?
• What is the 95% confidence interval for the proportion of all delinquent customer accounts at this manufacturing company?
• A simple random sample of 400 individuals provides 100 Yes responses. How do you find the standard error of the proportion?
• You measure the lifetime of a random sample of 64 tires of a certain brand. Suppose that the lifetimes for tires of this brand follow a normal distribution, with unknown mean μ and standard deviation σ = 5 kg. What is the 99% confidence interval?
• What is a 95-percent confidence interval for the mean one year extended warranty expenditure per automobile?
• What is the critical value that Zα/2 that corresponds to a 99% confidence level?
• In a poll of 1,000 randomly selected adults, 400 answered “yes” when asked if they planned to vote in the state election. What is the best point estimate of the population proportion of all adults who plan to vote in that election?
• How do you find the critical value Za/2 corresponding to a 97% confidence level?
• What happens to the precision of a confidence interval as the confidence level increases?
• What is the critical value za/2 that corresponds to a 94% confidence?
• Suppose you know σ and you want an 85 percent confidence level. What value would you use to multiply the standard error of the mean by?
• What is the critical value zalpha/2 that corresponds to 88% confidence level?
• What is the 95% confidence level for the following problem?
• Why can't a confidence level be 100%?
• How do confidence levels compare to significance levels?
• How does significance level relate to confidence level?
• Joggers 1 and 2 run. Jogger 1's mean run is 5.25 whereas Jogger 2's mean run is 4.20. What can we infer about Jogger 1 and 2? What can't we infer?
• A research firm wants to estimate the true population proportion of families having annual incomes that exceed $100,000 in a particular city. If it costs $20 to obtain each sample value, how large must the sampling budget be?"
• You want to estimate the proportion with a 95% confidence level with a margin of error of 3%; how large of a sample do you need?
• How do you find the margin of error for a poll, assuming that 95% confidence and pi= 0.4 for n = 45?
• How do you find the margin of error for a poll, assuming that 95% confidence and pi= 0.4 for n = 180?
• How do you find the margin of error for a poll, assuming that 95% confidence and pi= 0.4 for n = 450?
• Assume that a random sample is used to estimate a population proportion p. How do you find the margin of error E that corresponds to n=500, x=100, 95% confidence?
• How do you find the value of #E#, the margin of error, for #c=.90, n=10# and #s=3.1#?
• Of 238 employees selected randomly from one company, 10.08% of them commute by carpooling. How do you construct a 90% confidence interval for the true percentage of all employees of the company who carpool?
• For a dataset of size 58, the sample mean was calculated to be #barx=$2.75# and the sample standard deviation is #s=$0.86#. What is the 95% confidence interval for #mu#?
• Question #3cec6