The mean, median and mode of the distribution equal one another. The standard normal, or Z-distribution is a specific normal curve with a mean and variance . The value of the variable Z represents standard deviations from the mean. If the variable X represents individual observations in a population, the formula transforms the variable into Z. Sections 9.1, 9.2, 9.3, 9.5 Parameters are numerical characteristics of the population. The numerical characteristics of a sample are called sample statistics .
Sample statistics serve as estimates of the population parameters.
Unbiasedness means that, on average , the statistic will equal the population parameter . Typically there will be some difference between the sample statistic and population parameter. This difference is called Sampling Error . It is calculated from a sample and different samples taken from a population will typically generate different values of . follows a sampling distribution which assigns probability to the different possible values of the variable. The variance of is and the standard deviation is where n is the size of the sample taken to calculate .