#### Basic Statistics I – Definitions of commonly used Statistical Terms

**Average**– Also called the**mean**, it is the arithmetic average of all of the sample values. It is calculated by adding all of the sample values together and dividing by the number of elements (n) in the sample.**Central Tendency**– A measure of the point about which a group of values is clustered; two measures of central tendency are the mean, and the median.**Characteristic**– A process input or output which can be measured and monitored.**Cycle Time**– The total amount of elapsed time expended from the time a task, product or service is started until it is completed.**Long-term Variation**– The observed variation of an input or output characteristic which has had the opportunity to experience the majority of the variation effects that influence it.**Median**– The middle value of a data set when the values are arranged in either ascending or descending order.**Mode**: The data point which occurs at maximum frequency**Lower Control Limit (LCL)**– for control charts: the limit above which the subgroup statistics must remain for the process to be in control. Typically, 3 standard deviations below the central tendency.**Lower Specification Limit (LSL)**– The lowest value of a characteristic which is acceptable.**Range**– A measure of the variability in a data set. It is the difference between the largest and smallest values in a data set.**Specification Limits**– The bounds of acceptable performance for a characteristic.**Standard Deviation**– One of the most common measures of variability in a data set or in a population. It is the square root of the variance.**Trend**– A gradual, systematic change over time or some other variable.**Upper Control Limit (UCL) for Control Charts**– The upper limit below which a process statistic must remain to be in control. Typically this value is 3 standard deviations above the central tendency.**Upper Specification Limit (USL)**– The highest value of a characteristic which is acceptable.**Variability**– A generic term that refers to the property of a characteristic, process or system to take on different values when it is repeated.**Variables**– Quantities which are subject to change or variability.**Variable Data**– Data which is continuous, which can be meaningfully subdivided, i.e. can have decimal subdivisions.**Variance**– A specifically defined mathematical measure of variability in a data set or population. It is the square of the standard deviation.