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A statistic (singular) or sample statistic is any quantity computed from values in a sample, often the mean. Technically speaking, a statistic can be calculated by applying any mathematical function to the values found in a sample of data.In this case, '52%' is a statistic, namely the percentage of Republicans in the survey sample who believe in global warming. The population is the set of all Republicans in the United States, and the parameter is the percentage of all Republicans, not just those surveyed, who believe in global warming.In this example, '5.6 days' is a statistic, namely the mean length of stay for our sample of 20 hotel guests. The population is the set of all guests of this hotel, and the parameter is the mean length of stay for all guests. A statistic (singular) or sample statistic is any quantity computed from values in a sample, often the mean. Technically speaking, a statistic can be calculated by applying any mathematical function to the values found in a sample of data. In statistics, there is an important distinction between a statistic and a parameter. 'Parameter' refers to any characteristic of a population under study. When it is not possible or practical to directly measure the value of a population parameter, statistical methods are used to infer the likely value of the parameter on the basis of a statistic computed from a sample taken from the population. When a statistic is used to estimate a population parameter, is called an estimator. It can be proved that the mean of a sample is an unbiased estimator of the population mean. This means that the average of a large number of sample means will tend to converge to the true mean of the population. Formally, statistical theory defines a statistic as a function of a sample where the function itself is independent of the unknown estimands; that is, the function is strictly a function of the data. The term statistic is used both for the function and for the value of the function on a given sample. When a statistic (a function) is being used for a specific purpose, it may be referred to by a name indicating its purpose: in descriptive statistics, a descriptive statistic is used to describe the data; in estimation theory, an estimator is used to estimate a parameter of the distribution (population); in statistical hypothesis testing, a test statistic is used to test a hypothesis. However, a single statistic can be used for multiple purposes – for example the sample mean can be used to describe a data set, to estimate the population mean, or to test a hypothesis.

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