Parameter

A measure computed from the entire population as long as the population does not change

Statistic

A measure computed from a sample that has been selected from a population. The value of the statistic will depend on which sample is selected

Mean

All the values added together divided by the total amount of them

Population Mean

The average for all values in the population computed by dividing the sum of all values by the population size

Sample Mean

The averge for all values in the sample computed by dividing the sum of all sample values by the sample size

Median

The median is a center value that divides the data into two halves

Data Array

Data that have been arranged in numerical order

Symmetric Data

Data sets whose values are evenly spread around the center. For symmetric data the mean and the median are equal

Skewed Data

Due to major numbers the number is dramtically shifted to the right or left

Right Skewed Data

The data distribution is right skewed the mean is larger than the median

Left Skewed Data

Data skewed to the left

Mode

The mode is the value in data set that occurs most frequently

Weighted Mean

The mean value of data values that have been weighted according to their relative importance

Percentiles

The percentile in the data array is a vlaue that breaks the data set into two parts. The lower contains the p and the upper contains at least 100 minus p% and the 50 percentile is the median

Quartiles

Quartiles in a data array are those values that break the data into four equal sized groups and the median corresponds to the second quartile

Variation

A set of data exhibits variation if all the data are not the same value

Range

Is the highest minus the lowest

Interquartile Range

The interquartile range is the third minus the first quartile

Variance

The population variance is the average of the squared distances of the data values from the mean

Standard Deviation

The standard deviation is the positive square root of the variance

Coefficent Of Variation

The ratio of the standard deviation to the mean expressed as a percentage. The coefficent of variation is used ot measure variation relative to the mean

Standarized Data Values

The number of standard deviations a value is from the mean sometimes referred to as z scores