Sample Variance

Definition

The sample variance is a measure of the spread or dispersion of a set of data points around the sample mean. It represents the average squared deviation of the data points from the sample mean, providing insight into the variability within a sample.

5 Must Know Facts For Your Next Test

1. The sample variance is calculated by summing the squared differences between each data point and the sample mean, and then dividing the result by the number of data points minus one.
2. The sample variance is an unbiased estimator of the population variance, meaning that it provides an accurate estimate of the true variance in the population.
3. The sample variance is a crucial statistic in hypothesis testing, as it is used to determine the standard error of the sample mean and to construct confidence intervals.
4. When the population standard deviation is unknown, the sample variance is used to estimate the population variance in statistical analyses, such as in the two-sample t-test and the F-test.
5. The sample variance is sensitive to outliers, as the squared differences between the data points and the sample mean can be greatly influenced by extreme values.

Review Questions

• Explain how the sample variance is calculated and its relationship to the sample mean.
  • The sample variance is calculated by first finding the difference between each data point and the sample mean, squaring those differences, and then summing the squared differences. This sum is then divided by the number of data points minus one. The sample variance represents the average squared deviation of the data points from the sample mean, providing a measure of the spread or dispersion of the data.
• Describe the role of the sample variance in hypothesis testing, particularly in the context of unknown population standard deviations.
  • When the population standard deviation is unknown, the sample variance is used as an estimate of the population variance in statistical analyses, such as the two-sample t-test and the F-test. The sample variance is used to calculate the standard error of the sample mean, which is then used to construct confidence intervals and perform hypothesis tests. The accuracy of these statistical inferences relies heavily on the sample variance being a good estimate of the true population variance.
• Analyze the potential impact of outliers on the sample variance and discuss strategies for mitigating their influence.
  • The sample variance is sensitive to outliers, as the squared differences between the data points and the sample mean can be greatly influenced by extreme values. This can lead to an overestimation of the true variability in the data. To mitigate the impact of outliers, researchers may consider using robust statistical methods, such as trimmed means or winsorized variances, which reduce the influence of extreme observations. Additionally, carefully examining the data for outliers and considering their potential causes can help researchers make informed decisions about their inclusion or exclusion in the analysis.

Related terms

Sample Mean: The sample mean is the arithmetic average of a set of data points, calculated by summing all the values and dividing by the total number of data points.

Standard Deviation: The standard deviation is the square root of the sample variance, and it measures the average amount of variation or dispersion of the data points from the sample mean.

Population Variance: The population variance is a measure of the spread or dispersion of all the data points in the entire population, as opposed to just the sample.