# Data

**Data** are characteristics or information, usually numerical, that are collected through observation. ^{}In a more technical sense, data are a set of qualitative or quantitative variables about one or more persons or objects, while a **datum** (singular of data) is a single value of a single variable.

## Types of Data

**Qualitative data:** is non-numerical, eg “it was fun", "blue".

**Quantitative data:** is numerical. Quantitative data can be discrete or continuous.

**Discrete data:** is data which takes specific (discrete) values, eg “number of accidents”, "points in the IB diploma".

**Continuous data:** is data which can take a full range of values, eg "height", “speed".

Population

**Population:** all members of a defined group.**Sample:** a subset of the population, a selection of individuals from the population.

**Biased sampling** is where the method may cause you to draw misleading conclusions about the population.

### Survivorship Bias - an example of biased sampling.

## Types of sampling

**Simple random sampling:** every member of the population is equally likely to be chosen. For example, allocate each member of the population a number. Then use random numbers to choose a sample.

**Systematic sampling:** find a sample of size \(n\) from a population of size \(N\) by selecting every \(k\)th member where \(k = \frac{N}{n}\) to the nearest whole number.

**Stratified sampling:** is selecting a random sample where numbers in certain categories proportional to the numbers in the population. (E.G. in polls)

### Stratified Polling in New Zealand

## Mean, Median, Mode

## Standard Deviation (TBC)

# Editors

- joeClinton - 174 words.
- CD_FER - 348 words.

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