Exam 7: Sampling and Sampling Distributions

Suppose 35% of homes in a Miami, Florida, neighborhood are under water (in other words, the amount due on the mortgage is larger than the value of the home). There are 160 homes in the neighborhood and 30 of those homes are owned by your friends. What is the probability that fewer than 30% of your friends' homes are under water?

Over the entire six years that students attend an Ohio elementary school, they are absent, on average, 28 days due to influenza. Assume that the standard deviation over this time period is σ = 9 days. Upon graduation from elementary school, a random sample of 36 students is taken and asked how many days of school they missed due to influenza. What is the expected value for the sampling distribution of the number of school days missed due to influenza?

Bias can occur in sampling. Bias refers to ________.

Suppose that, on average, electricians earn approximately µ = $54,000 per year in the United States. Assume that the distribution for electricians' yearly earnings is normally distributed and that the standard deviation is σ = $12,000 dollars. What is the probability that the average salary of four randomly selected electricians is more than $50,000 but less than $60,000?

A ski resort gets an average of 2000 customers per weekday with a standard deviation of 800 customers. Assume the underlying distribution is normal. What is the probability a ski resort averages between 1500 customers and 3000 customers per weekday over the course of four weekdays?

According to the Bureau of Labor Statistics it takes an average of 16 weeks for young workers to find a new job. Assume that the probability distribution is normal and that the standard deviation is two weeks. What is the probability that 20 young workers average less than 15 weeks to find a job?

For any population proportion p, the sampling distribution of will be approximately normal if the sample size n is sufficiently large. As a general guideline, the normal distribution approximation is justified when np ≥ 5 and n(1 − p) ≥ 5.

Successful firms must focus on the quality of the products and services they offer. Which factor or factors contribute to the quest for quality?

The standard deviation of suggests that the variation between observations is smaller than the variation between averages.

Nonresponse bias occurs when ________.

If is normally distributed then we can transform it into a(n) ________ normal random variable.

A university administrator expects that 25% of students in a core course will receive an A. He looks at the grades assigned to 60 students. The probability that the proportion of students that receive an A is 0.20 or less is ________.

Professor Elderman has given the same multiple-choice final exam in his Principles of Microeconomics class for many years. After examining his records from the past 10 years, he finds that the scores have a mean of 76 and a standard deviation of 12. Professor Elderman offers his class of 36 a pizza party if the class average is above 80. What is the probability that he will have to deliver on his promise?

In cluster random sampling, the population is first divided up into mutually exclusive and collectively exhaustive groups, called clusters. A cluster sample includes randomly selected observations from each cluster, which are proportional to the cluster's size.

The detection approach to statistical quality control ________.

In stratified random sampling, the population is first divided up into mutually exclusive and collectively exhaustive groups, called strata. A stratified sample includes randomly selected observations from each stratum, which are proportional to the stratum's size.

The ________ variation in the production process is caused by specific events or factors that can usually be identified and eliminated.

The labor force participation rate is the number of people in the labor force divided by the number of people in the country who are of working age and not institutionalized. The BLS reported in February 2012 that the labor force participation rate in the United States was 63.7% (Calculatedrisk.com). A marketing company asks 120 working-age people if they either have a job or are looking for a job, or, in other words, whether they are in the labor force. For the company's sample, the probability that the proportion of people who are in the labor force is greater than 0.65 is ________.

In early 2012, the U.S. Congress approval rating was approximately 10% (Reuters.com). In a poll of 400 Americans, what is the probability that their approval rating is between 8% and 12%?

Peggy would like to conduct a survey in her neighborhood to get homeowners' opinions on the Delmarva proposal to switch to natural gas. Which of the following is an example of a convenience sample?