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Suppose that, when taking a sample of five students' heights, you get a sample mean of \(183 \mathrm{~cm}\). This sample mean is far higher than the class-wide (population) mean. Does that prove that your sample is biased? Explain. What else could have caused this high mean?

Short Answer

Expert verified
No, the fact that the sample mean is higher than the population mean doesn't prove the sample is biased. It could be due to randomness or other factors in the data collection process. To detect bias, we would need to look at whether the average of many sample means deviates from the population mean in some systematic way.

Step by step solution

01

Understand the Terms

A sample is a subset of a population that is used to represent the population. A sample mean is the average of the data points in a sample. The population mean is the true average of the population, it is what you would get if you were able to measure the entire population. A biased sample is one that doesn’t accurately represent the population. In statistics, bias is an error that skews data in one way or another.
02

Relate Sample Mean and Population Mean

If the sample mean is higher or lower than the population mean, it doesn’t necessarily mean that the sample is biased. This is because a single sample can have a mean that is different from the population mean due to random variation.
03

Discuss Possible Causes of High Mean

The high sample mean could be due to randomness in this particular sample selection; maybe by chance, taller students were chosen. Or perhaps some part of the data collection process was imperfect. However, obtaining a sample mean that is higher than the population mean on its own isn't evidence of a bias. Bias occurs when there is a systematic error in the data collection process.
04

Understand Need for Larger Sample Size

If we were to take many samples from the population, we would expect the average of these sample means to be close to the population mean. If we consistently get a higher mean when we take many samples from the population, that could suggest bias.

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Key Concepts

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

Statistics Education
Statistics education is a fundamental component of a modern curriculum that empowers students to understand data, assess trends, and make informed decisions based on quantitative analysis. It involves teaching methodologies for collecting, analyzing, and interpreting data. A clear grasp of these techniques is crucial for distinguishing between sample statistics, like the sample mean, and population parameters, such as the population mean.
In our exercise example, understanding these concepts could help students recognize the variability inherent in sampling and appreciate the difference between an isolated high sample mean and signs of a consistent bias. This distinction is essential when interpreting data and applying statistical inferences in real-world scenarios.
Biased Sample
A biased sample is a selection from a population that does not accurately represent the whole. This can skew the results of a study and lead to incorrect conclusions. Bias can enter a sample in various ways, such as through non-random selection processes or excluding certain segments of the population.
In the context of our problem, a high sample mean of students' heights alone does not confirm bias. Rather, one must look for evidence of a systematic error or a flawed data collection process. For instance, if only basketball players were selected for the sample, this would introduce bias, as their heights may be above average compared to the general student population.
Random Variation
Random variation refers to the natural fluctuations that occur when taking different samples from the same population. It's an expected part of sampling processes and does not indicate a fundamental problem with the data.
For example, suppose five students are randomly chosen from a class, and their average height is significantly above the class mean. This could simply be due to the random chance that these particular students happen to be taller, rather than indicative of a biased sample. A robust understanding of random variation is crucial for students, as it allows them to differentiate between mere coincidences in data collection and patterns that could suggest an underlying bias.
Systematic Error
Systematic error is a consistent, repeatable error associated with faulty equipment, flawed methodology, or inherent bias in the data collection process. Unlike random variation, it does not even out over repeated trials or samples, but rather skews all data in a single direction.
When we witness a discrepancy between a sample mean and a population mean, we need to investigate whether this is due to random variation or systematic error. If every sample drawn consistently leads to a higher mean, then the possibility of systematic error should be considered. Students must be educated to look for patterns in their data collection that could hint at such errors, like consistently overlooking smaller individuals when measuring height.

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Most popular questions from this chapter

A random sample of likely students for higher studies showed that \(28 \%\) would want to pursue economics. The margin of error is \(4.5\) percentage points with a \(95 \%\) confidence level. a. Using a carefully worded sentence, report the \(95 \%\) confidence interval for the percentage of students who plan to choose economics. b. Is there evidence that there will not be enough students for economics? c. Suppose the survey was conducted in one section out of 12 sections of the classes eligible to participate in the survey. Explain how that would affect your conclusion.

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