The range for a set of data is estimated to be 36 a. What is the planning value for the population standard deviation? b. At \(95 \%\) confidence, how large a sample would provide a margin of error of \(3 ?\) c. At \(95 \%\) confidence, how large a sample would provide a margin of error of \(2 ?\)

The range of data is a measure of dispersion or variability that indicates the difference between the highest and lowest values in a dataset. It is calculated simply by subtracting the smallest value from the largest value. Understanding the range is fundamental in statistics because it provides a quick sense of the spread of values in the dataset.

For example, in a set of test scores where the highest score is 95 and the lowest is 55, the range would be 40 points (95 - 55 = 40). However, the range doesn't take into account how the values are distributed between the highest and lowest points. This is where other measures, like standard deviation, come into play as they consider the variation of each data point from the mean.

When estimating the population standard deviation from the range, as shown in the exercise solution, the range is divided by an interquartile range scaling factor, often 4, to approximate the standard deviation. This method assumes a bell-shaped distribution (normal distribution) of the data.

In statistics, the margin of error measures the extent of the possible discrepancy between the sample estimate and the actual population parameter. It is an expression of the amount of random sampling error in the results of a survey or experiment. The margin of error is critically important in understanding how reliable the findings are from sample data.

The formula for margin of error is essentially a function of three key elements: the standard deviation of the population (\( s \)), the size of the sample (\( n \)), and the level of confidence one wants to have in the estimate. A higher confidence level or a lower margin of error requires a larger sample size. Conversely, if a researcher is willing to accept a higher margin of error, the required sample size can be smaller.

Understanding the relationship between the margin of error and sample size is crucial, particularly in planning studies and surveys to ensure sufficient precision of the results without unnecessarily oversampling.

Calculating the correct sample size is essential for obtaining statistically significant results. It is a balance between precision, confidence, and the resources available. The formula for calculating sample size takes into account the desired margin of error, the standard deviation of the population, and the z-value corresponding to the desired level of confidence.

To obtain the sample size, statisticians rearrange the margin of error formula, isolating the sample size (\( n \)). This produces a formula that predicts how large a sample is needed to estimate the population parameter with a specified margin of error and confidence level. In practical terms, a larger sample will produce a more precise estimate but will also require more resources to collect.

As observed in the provided exercise, the required sample size increases as the desired margin of error decreases. It's also important to round up the calculated sample size to the next whole number, as you cannot have a fraction of a sample. When planning experiments or surveys, the calculation of sample size is a fundamental step that influences the quality and credibility of the findings.