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1 Variables and distributions
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What are the definitions of a variable?
1. An outcome (or response or dependent) variable. This is the variable that is the main interest in our study.
2. An explanatory (or exposure or independent) variable. This is a variable that changes the value of our outcome. -
Which categorical or binary variables are there?
- Categorical
- Binary
- Ordered categorical -
What is a binary variable?
The simplest type of categorical variable which has only two categories, e.g. sex, parasitaemia, anaemia, IgE seropositive -
What is an ordered categorical variable?
A variable that has different categories which are naturally ordered on some scale, e.g. severity of disease, performance scores for HIV-patients, age-groups, pain scale -
What is the definition of a quantitative variable?
A variable that describes a quantity which can be counted or measured numerically. -
What is a continuous variable?
A variable that can be quantified on a well-defined scale with units and do not have any restriction on the set of values that they can take, e.g. birth weight -
What is a discrete variable?
A variable that can be quantified on a well-defined scale with units but the values that they can take are from a finite set, e.g. number of live-born children -
How is data presented in a pie chart?
In a pie chart the frequencies or the percentages are represented by the angles in different sectors (slices) of a circle; the total circle is 100% -
How is data presented in a bar chart?
In a bar chart the numbers of percentages are represented by the lengths of the bars -
Which ways can quantitative data be presented?
- Histogram
- Cumulative frequency curves
- Scatter plots
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