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Safe cities Allstate Insurance Company identified the 10 safest and 10 least- safe U.S. cities from among the 200 largest cities in the United States, based on the mean number of years drivers went between automobile accidents. The cities on both lists were all smaller than the 10 largest cities. Using facts about the sampling distribution model of the mean, explain why this is not surprising.

Short Answer

Expert verified
The 10 safest and the 10 least-safe U.S cities being smaller than the 10 largest cities can be attributed to the density and variation in the distribution of the mean years between automobile accidents. In larger cities, due to the larger sample size, the data is more concentrated around the mean resulting in fewer cases of extreme safety or lack of safety. Conversely, smaller cities, due to smaller sample size, have more variation, hence, they appear on both ends of the spectrum.

Step by step solution

01

Understanding the Sampling Distribution Model

A sampling distribution model is a probability distribution of a statistic obtained through a large number of samples drawn from a specific population. The mean of multiple samples, in this case, the period between automobile accidents, will generally form a normal distribution pattern. This is due to the Central Limit Theorem which states that the distribution of sample means will be normally distributed if the sample size is large enough.
02

Correlating with Population Size

In the case of large cities, the sample size (i.e., the number of drivers) is much larger compared to smaller cities. This larger sample size leads to the distribution being more concentrated around the mean.
03

Interpreting the Result

In large cities, the increased sample size results in fewer outliers, meaning fewer cases of extreme safety or lack of safety. On the other hand, smaller cities have more variation, making them more likely to show up on the list of cities with the longest and shortest period between automobile accidents. Thus the 10 safest and the 10 least-safe cities are more likely to fall among smaller cities.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Central Limit Theorem
The Central Limit Theorem (CLT) is a fundamental principle in statistics that helps us understand the behavior of sample means. It states that if you take sufficiently large samples from a population, the distribution of the sample means will tend to form a normal distribution, even if the original population is not normally distributed.
This explains why, when analyzing a topic such as the time between driver accidents, the average across many samples will generally look like a bell curve.
This concept is crucial in statistics as it guarantees that we can make inferences about the population mean based on the sample mean even when data is not perfectly normal initially.
Sample Size
Sample size plays a critical role in statistical analysis because it impacts the reliability of your findings. A larger sample size generally results in a more accurate representation of the population, as it reduces the margin of error.
When applying the Central Limit Theorem, larger samples tend to produce a distribution of means that is more tightly clustered around the actual population mean. This clustering makes the distribution appear more normal, reinforcing the principles of the CLT.
In the context of the exercise, cities with a larger population (or larger sample size of drivers) will have a more typical and less variable distribution of driver accident intervals compared to smaller cities.
Normal Distribution
Normal distribution is a statistical concept that describes the spread of a set of data. Often visualized as a bell-curve, it represents how data tend to be distributed around the mean with most values clustering near the average and fewer and fewer going towards the extremes.
The Central Limit Theorem assures us that the distribution of the sample means will be approximately normal when the sample size is large enough.
This behavior is predictable and is used extensively in hypothesis testing and estimation because it provides a basis for making predictions about a population from a sample.
Population Size
Population size refers to the number of individuals or elements within the total group from which a sample is drawn. In statistics, understanding the population size helps inform us about variability and expected outcomes.
Smaller population sizes typically have more variability between individual sample means, leading to a wider spread in the distribution of means.
This variability can explain why smaller cities might appear more frequently on lists of extremes, such as the safest or least-safe cities for drivers. The population size affects how tightly or loosely the sample means cluster around the actual population mean.
Outliers
Outliers are data points that fall far from the other observations in a dataset. They can occur due to variability in the measurement or may indicate experimental errors.
They are particularly significant because they can have a disproportionate effect on the mean and other statistical measurements.
In the context of the exercise, larger cities, having more data, are less likely to be impacted by outliers, making their data distribution more stable. Smaller cities are more susceptible to outliers because less data increases the chance that a single unusual data point will skew results, leading to them appearing more extreme in terms of safety rankings.

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