Statistics deals with data.

It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. Arthur Conan Doyle, Sherlock Holmes

Data consists of observations collected from a population or process. It may represent a numerical value (quantitative) or a label (qualitative). It can be studied in:

  • descriptive statistics, which summarise large sets of data, or

  • inferential statistics, which draw conclusions from data subject to random variation.

Correlation and Causation

Correlation quantifies the degree to which two variables move in tandem, while causation implies that changes in one variable directly influence another. Correlation is necessary for causation, but it is not sufficient.

Glossary

  • Mean (a.k.a. expected value, expectation): The arithmetic average of data points.

  • Median: The middle value when the data is ordered.

  • Mode: The most frequently occurring value in a dataset.

  • Population: All people or items with the characteristics one wishes to understand.

  • Probability: A number between 0 and 1 that represents how likely an event is to occur.

  • Sample: A subset of a population.

  • Variable: A characteristic or quantity that can be measured, observed, or controlled.

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