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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