Refresher - Some Basic Definitions
DEF: The Frequency (F)
How often each value ( event or observation) has occurred.
DEF: The Relative Frequency (RF)
Relative Frequency is another term for proportion; it is the value calculated by dividing the number of times an event occurs by the total number of times an experiment is carried out.
RF=FrequencyTotal number of observations
DEF: Grouped data, Class Intervals
In statistics, the range of each class of data, used when arranging large amounts of raw data into grouped data. To obtain an idea of the distribution, the data are broken down into convenient classes, which must be mutually exclusive and are usually equal in width.
For example, let's assume that you have collected some data ranging from 0 to 100. You may group the data into different classes. A symbol defining a class such as 1- 20; 21- 40; 41- 60; is called a class interval.
DEF: Class Limits
Separate one class in a grouped frequency distribution from another. The limits could actually appear in the data and have gaps between the upper limit of one class and the lower limit of the next. i.e. the end numbers for each are called class limits.
DEF: Class Boundaries
Separate one class in a grouped frequency distribution from another. The boundaries have one more decimal place than the raw data and therefore may not appear in the data. There is no gap between the upper boundary of one class and the lower boundary of the next class.
Once again assume that you have collected some data ranging from 0 to 100. Further assume that class interval denote the If dollars are recorded to the nearest dollar, the class interval 21 - 40, for example, theoretically includes all measurements from 20.50 to 40.49. These numbers are called class boundaries.
In practice, the upper class boundary is obtained by adding the upper class limit of one class interval to the lower class limit of the next higher class and then dividing by 2.
The class width is the difference between the upper and lower boundaries of any class. The class width is also the difference between the lower limits of two consecutive classes or the upper limits of two consecutive classes.
DEF: Class Mark (Midpoint)
The class mark (or Midpoint) is the number in the middle of the class. It is found by adding the upper and lower limits and dividing by two. It can also be found by adding the upper and lower boundaries and dividing by two.
DEF: Range
Range is defined to be the difference between the largest and the smallest observations.
Statisticians use summary measures to describe patterns of data. Measures of central tendency refer to the summary measures used to describe the most "typical" value in a set of values.