A summary value calculated from a population is called what?

In statistics, a parameter is defined as a numerical summary of a population. A population includes all members of a specified group or data set. Parameters are fixed values, although in practice, they are often unknown because it is difficult or impossible to collect data from an entire population.

Common examples of parameters include the population mean (μ), population proportion (P), and population standard deviation (σ). For instance, if we wanted to calculate the average height of all students in a country, the value derived from the entire population would be a parameter.

In contrast, a statistic is a summary value calculated from a sample, which is a subset of the population. For example, if we measure the height of 100 students from the country and calculate the average, that value is a statistic, which estimates the population parameter.

The term sample refers to the subset of individuals selected for measurement, while population refers to the full group from which the sample is drawn. Understanding the distinction between parameter and statistic is fundamental in statistical analysis, as it helps researchers make inferences about large populations based on sample data.

Parameters are central to concepts like confidence intervals, hypothesis testing, and regression analysis. For instance, knowing the population mean (parameter) allows statisticians to assess how representative a sample is and to make predictions with quantified uncertainty.

Therefore, when a summary value is calculated from an entire population, it is called a parameter (Option A). This concept is foundational in statistics and research, as it differentiates population-level measures from sample-level measures, guiding data analysis and decision-making processes.