# Data Types

Describe the different types of data

Data are a series of observations or measurements. Can be either qualitative or quantitative.

## Qualitative Data

Using words as data rather than numbers, evaluating meaning and process. Common in the social sciences.

## Quantitative Data

Uses numbers, or can be coded numerically. Divided into multiple types, each with multiple subtypes.

• Categorical
Data exist in discrete categories without intrinsic order.
• e.g. Medical specialty (intensive care, emergency medicine, orthopaedics, cardiology)
• Descriptive statistics for categorical data can be reported using the absolute number for each category, percentages, or proportions
• Ordinal
Data exists in discrete categories with an intrinsic order, e.g. age groups (0-5, 6-10, 11-15...)
• Descriptive statistics for ordinal data are the same for categorical data, but they can also be summarised by the median and the range (e.g. median age group, age group range).
• Numeric
Data is an actual number. Can be subdivided into discrete or continuous:
• Discrete
Can only be recorded as an integer (whole number), e.g. number of hospital admissions.
• Dichotomous or binary data, which occurs when there are only two categories
• Continuous
Where data can assume any value (including fractions), e.g. white cell count.
• Continuous data can be further subdivided into interval or ratio data:
• Ratio data
Are expressed with reference to a rational zero, which is where zero means no measurement.
• e.g. Temperature in °K is a ratio variable, whilst temperature in °C is not
This is because 0°K means no temperature, whilst 0°C does not; e.g. 50°K is half the temperature of 100°K, but 50°C is not half the temperature of 100°C.
• Ratio variables can (unsurprisingly) be expressed as ratios, whilst interval variables can not
• Interval data
Do not have a rational 0 - this is just another point on the line (e.g. temperature in °C).

1. Myles PS, Gin T. Statistical methods for anaesthesia and intensive care. 1st ed. Oxford: Butterworth-Heinemann, 2001.
Last updated 2019-12-09