Measures of center: A measure of central tendency (measure of center) is a value that attempts to describe a set of data by identifying the central position of the data set (as representative of a "typical" value in the set). We are familiar with measures of central tendency called the mean, median and mode.
Mean: The mean is the average of the numbers: a calculated "central" value of a set of numbers. To calculate: Just add up all the numbers, then divide by how many numbers there are.
Median: The middle number (in a sorted list of numbers). To find the Median, place the numbers you are given in value order and find the middle number.
Measures of spread: Measures of spread describe how similar or varied the set of observed values are for a particular variable (data item). Measures of spread include the range, quartiles and the interquartile range, variance and standard deviation.
Range: The difference between the lowest and highest values. In {4, 6, 9, 3, 7} the lowest value is 3, and the highest is 9, so the range is 9 − 3 = 6.
Interquartile Range: In descriptive statistics, the interquartile range (IQR), also called the midspread or middle 50%, being equal to the difference between 75th and 25th percentiles, or between upper and lower quartiles, IQR = Q3 − Q1. In other words, the IQR is the 1st quartile subtracted from the 3rd quartile; these quartiles can be clearly seen on a box plot on the data.
5 number summary:For a set of data, the minimum, first quartile, median, third quartile, and maximum. Note: A boxplot is a visual display of the five number summary.
Histogram: A graphical display where the data is grouped into ranges (such as "40 to 49", "50 to 59", etc), and then plotted as bars. Similar to a Bar Graph, but in a Histogram each bar is for a range of data.
Box Plots: A box plot is a graphical rendition of statistical data based on the minimum, first quartile, median, third quartile, and maximum. The term "box plot" comes from the fact that the graph looks like a rectangle with lines extending from the top and bottom.
Bivariate data: Data for two variables (usually two types of related data).
Skew: When data has a "long tail" on one side or the other
Outlier: A value that "lies outside" (is much smaller or larger than) most of the other values in a set of data.
Standard Deviation: The Standard Deviation is a measure of how spread out numbers are. It is the square root of the Variance, and the Variance is the average of the squared differences from the Mean.
Two way frequency tables: A way to compare multiple pieces of related data.