---
title: Dichotomisation
description: "This is the extremely common situation in which we convert a continuous measurement into a binary: \"It's hot today\" rather than \"It's 40 degrees Celsius today\". #### Details Well \"clinical\" versus \"non-clinical\" is commoner in our fields. There are understandable…"
url: "https://www.psyctc.org/psyctc/glossary2/dichotomisation/"
updated: "2024-12-04"
category: All OM book glossary entries
---

# Dichotomisation

This is the extremely common situation in which we convert a continuous measurement into a binary: "It's hot today" rather than "It's 40 degrees Celsius today".

#### Details

Well "clinical" versus "non-clinical" is commoner in our fields. There are understandable reasons why we might do this but there are essentially no circumstances in which it is not throwing away a lot of information so both for individuals' data, and for analyses of aggregate data, we should be very wary of doing this. When analysing aggregate data the loss of power and precision as opposed to analysing the continuous scores can be quite severe.

The same issues apply when continuous scores are simplified to three, four or even five levels: trichotomisation, quadratomisation (?) and what I call quinchotomisation though the loss of power/precision gets less as the number of levels goes up.

#### Try also

[Aggregation](https://www.psyctc.org/psyctc/glossary2/aggregation/)
[Clinically significant change (CSC)](https://www.psyctc.org/psyctc/glossary2/clinically-significant-change-csc/)
Cutting points
[Estimate/estimation](https://www.psyctc.org/psyctc/glossary2/estimate-estimation/)
[Precision](https://www.psyctc.org/psyctc/glossary2/precision/)
Reliable and clinically significant change (RCSC)
[Reliable change index (RCI)](https://www.psyctc.org/psyctc/glossary2/reliable-change-index-rci/)
Statistical power

#### Chapters

Not covered in the OMbook.

#### Online resources

See my [Rblog](https://www.psyctc.org/Rblog/index.html) post ([dichotomisation](https://www.psyctc.org/Rblog/posts/2024-12-03-dichotomisation-1/)) for a simulation illustrating the issues.

#### Dates

First created 25.xi.24, updated with link to Rblog post 4.xii.24.