Mean

Mean is a measure of central tendency. Sum of numbers/total number of numbers

Mode

Mode is a measure of central tendency. Most common number

Median

Median is a measure of central tendency. Middle number

Central Tendency

Gives an indication of the "middle" of a set of data. it is measured using the mean, median and mode. Each of these is calculated differently and the one that is best to use depends on the data you have

Range

Range = Largest  smallest

Interquartile range

Upper quartile  lower quartile.

Shape of distribution

Shape refers to whether a data is normally distributed, skewed left/negatively or skewed right/positively
shape_of_distribution.jpg (image/jpg)

Outlier

A value that "lies outside" (is much smaller or larger than) most of the other values in a set of data.
For example in the scores 25,29,3,32,85,33,27,28 both 3 and 85 are "outliers".

Primary v Secondary Data

Primary data is data you collect yourself through survey/experiment/investigation.
Secondary data is data you find through a newspaper/website/etc. Basically data that someone else has collected

Categorical v Numerical

Categorical data is nonnumerical data and can be ordered or nominal
Numerical data has numbers and can be discrete or continuous

Bias

Bias occurs when the survey sample does not accurately represent the population.
The bias that results from an unrepresentative sample is called selection bias

Simple Random Sample

Random sampling is a procedure for sampling from a population in which:
(a) the selection of a sample unit is based on chance
(b) every element of the population has an equal chance of being selected.

Representativeness

It is the closeness of the sample to the population from which the sample has been taken

Population

A population is any entire collection of people, animals, plants or things from which we may collect data. It is the entire group we are interested in, which we wish to describe or draw conclusions about.

Sample

A sample is a group of units selected from a larger group (the population).

Parameter

A parameter is a value, usually unknown (and which therefore has to be estimated), used to represent a certain population characteristic

Statistic

A statistic is a quantity that is calculated from a sample of data.

Census

Collection of data from a whole population rather than just a sample

Sampling Variability

Difference (or variance) between sample statistics from different samples. Example: If I ask 10 people their height and find the mean height of those, it may well be different to the mean height of another 10 people I ask. This difference is sampling variability
