Question

SKILL BUILDER 2 In Exercises 3.45 to 3.48 , construct an interval giving a range of plausible values for the given parameter using the given sample statistic and margin of error. For \(p,\) using \(\hat{p}=0.37\) with margin of error 0.02 .

Short answer

The range of plausible values for parameter \(p\) lies in the interval [0.35, 0.39].

Step-by-step solution

Understand the terms

The sample statistic here is \(\hat{p}=0.37\). This is the approximate value of the parameter \(p\) based on the collected data. The margin of error is 0.02, which gives an estimate of the range within which the real parameter value is expected to fall.

Calculate the lower limit of the interval

Subtract the margin of error from the sample statistic. That is, \(0.37 - 0.02 = 0.35\). So, the lower limit of the interval is 0.35.

Calculate the upper limit of the interval

Add the margin of error to the sample statistic. That is, \(0.37 + 0.02 = 0.39\). So, the upper limit of the interval is 0.39.

Key concepts

Margin of Error

The margin of error is a crucial statistic in understanding the uncertainty in a sample estimate. It indicates the extent to which the sample statistic, such as the sample proportion, may differ from the true population parameter due to sampling variability.

Imagine you're trying to measure the length of a table with a ruler that only measures whole centimeters. If the table's true length falls between two markings on the ruler, your measurement could be off by up to half a centimeter. This half centimeter is akin to the margin of error—it shows the possible discrepancy between the measure taken and the actual measurement.

When we estimate the proportion of a population that has a particular characteristic (\( p \)), and we've calculated a sample proportion (\( \text{\hat{p}} = 0.37 \)), we incorporate the margin of error to acknowledge that our sample might not perfectly represent the entire population. Affirming that our estimate lies within the interval formed by adding and subtracting the margin of error from our sample proportion provides a range that is likely to contain the true population proportion within a certain confidence level.

Sample Statistic

The sample statistic serves as a snapshot of the bigger picture—essentially, it's the 'sneak peek' of the target population's parameter we're trying to estimate. It's derived from a subset of the population, known as the sample, and is used to make inferences about the larger group.

For example, if we want to gauge the popularity of a new flavor of ice cream, we might offer taste tests to a group of people. The proportion of the group that enjoys the flavor (\( \text{\hat{p}} \)) would be our sample statistic. This gives us an insight into the possible appeal across all ice cream lovers, assuming our sample is representative. It is important to remember that the sample statistic, like any measurement from a sample, is a single point estimate of the true population value and carries with it a degree of uncertainty, which is why we employ margins of error and confidence intervals as precautions against this inherent uncertainty.

Parameter Estimation

Parameter estimation is the process of using sample data to infer or predict a range for a population characteristic, or parameter. Think of it as a detective trying to figure out the size of a footprint from clues rather than seeing the foot itself. We never observe the population parameter directly; instead, we use the evidence we have—the sample statistic—to make an educated guess about the parameter we're interested in.

In the realm of statistics, the parameter is a fixed value that describes a certain aspect of a population, such as the proportion of voters who will vote for a particular candidate. However, since it's not feasible to poll every voter, statisticians will survey a sample and use the responses to estimate the proportion for the entire voter population. The estimate will not be exact, which is why we also provide a range (the confidence interval) that we believe, with a degree of certainty, contains the true parameter.

Confidence Interval Calculation

A confidence interval is the range of values, derived from the sample statistic, within which the true population parameter is expected to fall a certain percentage of the time. It offers a calculated gamble or a bet on where the true value lies. It factors in the sample statistic, such as a sample mean or proportion, and incorporates the sampling variability represented by the margin of error.

To calculate a confidence interval, one would typically follow these steps: identify the sample statistic, determine the margin of error, and then create the range by adding and subtracting the margin of error from the sample statistic. For instance, with a sample proportion (\( \text{\hat{p}} = 0.37 \)) and a margin of error of 0.02, the confidence interval ranges from the lower boundary (\( 0.37 - 0.02 = 0.35 \text{\hat{p}} \text{\hat{p}} 0.35 \)) to the upper boundary (\( 0.37 + 0.02 = 0.39 \)).

The 'confidence' in the interval reflects our trust level in the process over repeated sampling; it is not a guarantee about any single interval. When we say, for example, a 95% confidence interval, we mean that if we were to take many samples and build an interval from each, approximately 95% of these intervals would contain the true population parameter—a fundamental reassurance in statistical inference.