Featured below is a series of introductory resources for students and professionals getting started with statistics.

1. Normal Distribution

Data can be “distributed” (spread out) in different ways. It can be spread out more on the left, or more on the right, or it can be all jumbled up.

But there are many cases where the data tends to be around a central value with no bias left or right, and it gets close to a “Normal Distribution” as shown in the graphic here.

2. Log-Normal Distribution

In probability theory, a log-normal distribution is a probability distribution of a random variable whose logarithm is normally distributed. If Y is a random variable with a normal distribution, then X = exp(Y) has a log-normal distribution; likewise, if X is log-normally distributed, then Y = log(X) is normally distributed. (This is true regardless of the base of the logarithmic function: if loga(Y) is normally distributed, then so is logb(Y), for any two positive numbers a, b ≠ 1.)

3. Mean, Median & Mode

The mean (average) of a data set is found by adding all numbers in the data set and then dividing by the number of values in the set. The median is the middle value when a data set is ordered from least to greatest. The mode is the number that occurs most often in a data set.