Writing for Science Students by Jennifer Boyle

Author:Jennifer Boyle
Language: eng
Format: epub
Publisher: Macmillan Education UK

Different types of data, and how to present them

Staff who mark first-year reports frequently comment on the choice of graphs their students have used. The most common errors are to do with using the wrong type of graph in the first place, or using the right type of graph but misrepresenting the relationship being investigated.

Before we look at ways to represent data, let’s first look at the different types of data.

Types of data

Categorical vs continuous

A very large part of your decision about how to represent your data will depend on whether it measures something on a sliding scale, or whether it measures something that’s measured in separate categories.

Heights, weights, electrical potentials, volumes, concentrations – these are all quantities that can take any value at all between the relevant maximum or minimum for the thing being measured. Yes, we measure them with scales that are divided into steps like metres or centimetres, or volts or millivolts, but those are artificial divisions put in place by the scientists who first devised those scales. The physical quantities are not limited to only the values that our tools can distinguish. These quantities are referred to as continuous variables and we can plot them on certain types of axes.

Nationality, hair colour, subatomic particle type – these are all variables which can either be one thing or another. Yes, someone’s nationality can be mixed, but they would either declare themselves to be predominantly one nationality, or they would declare themselves to be a mix of A, B and C, and this mixture would then be their category. Likewise, we give different names to hair colours and don’t measure them along a quantitative scale, and subatomic particles must be of one type or another. Categorical variables like these are plotted on different types of axes.

There are other ways of breaking down continuous and categorical variables (you may have heard of terms like ordinal and discrete) but the concepts of continuous and categorical are enough for us to deal with for now.

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