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Explain the difference between \(\sigma\) and \(\sigma_{\bar{x}}\) and between \(\mu\) and \(\mu_{\bar{x}}\)

Short Answer

Expert verified
σ is the standard deviation of a population and μ is the mean of the population. σ_{\bar{x}} is the standard deviation of the sample means, also known as the standard error, and μ_{\bar{x}} is the average of the sample means from the population. Hence, 'σ' and 'μ' pertains to the entire population while 'σ_{\bar{x}}' and 'μ_{\bar{x}}' pertain to statistical samples taken from the population.

Step by step solution

01

Understanding σ and σ_{\bar{x}}

The symbol σ stands for the population standard deviation, it quantifies the amount of variation in a set of data values. While σ_{\bar{x}}, also known as the standard error, represents the standard deviation of the distribution of the sample means. It quantifies the precision with which the mean of a sample estimates the mean of the population.
02

Understanding μ and μ_{\bar{x}}

The symbol μ is used to represent the population mean, which is the average of all values in the population. On the other hand, μ_{\bar{x}} is the mean of the sample means, that signifies the average of all the sample means from the population.

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Most popular questions from this chapter

The time that a randomly selected individual waits for an elevator in an office building has a uniform distribution over the interval from 0 to \(1 \mathrm{~min}\). It can be shown that for this distribution \(\mu=0.5\) and \(\sigma=0.289\). a. Let \(\bar{x}\) be the sample average waiting time for a random sample of 16 individuals. What are the mean and standard deviation of the sampling distribution of \(\bar{x}\) ? b. Answer Part (a) for a random sample of 50 individuals. In this case, sketch a picture of a good approximation to the actual \(\bar{x}\) distribution.

The article "Should Pregnant Women Move? Linking Risks for Birth Defects with Proximity to Toxic Waste Sites" (Chance [1992]: 40-45) reported that in a large study carried out in the state of New York, approximately \(30 \%\) of the study subjects lived within 1 mi of a hazardous waste site. Let \(\pi\) denote the proportion of all New York residents who live within 1 mi of such a site, and suppose that \(\pi=.3\). a. Would \(p\) based on a random sample of only 10 residents have approximately a normal distribution? Explain why or why not. b. What are the mean value and standard deviation of \(p\) based on a random sample of size \(400 ?\) c. When \(n=400\), what is \(P(.25 \leq p \leq .35)\) ? d. Is the probability calculated in Part (c) larger or smaller than would be the case if \(n=500 ?\) Answer without actually calculating this probability.

An airplane with room for 100 passengers has a total baggage limit of 6000 lb. Suppose that the total weight of the baggage checked by an individual passenger is a random variable \(x\) with a mean value of \(50 \mathrm{lb}\) and a standard deviation of \(20 \mathrm{lb}\). If 100 passengers will board a flight, what is the approximate probability that the total weight of their baggage will exceed the limit? (Hint: With \(n=100\), the total weight exceeds the limit when the average weight \(\bar{x}\) exceeds \(6000 / 100\).)

A manufacturing process is designed to produce bolts with a 0.5-in. diameter. Once each day, a random sample of 36 bolts is selected and the diameters recorded. If the resulting sample mean is less than \(0.49\) in. or greater than \(0.51\) in., the process is shut down for adjustment. The standard deviation for diameter is \(0.02\) in. What is the probability that the manufacturing line will be shut down unnecessarily? (Hint: Find the probability of observing an \(\bar{x}\) in the shutdown range when the true process mean really is \(0.5\) in.)

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