Chapter 2: Variable

Definition of Variable in Biostatistics

Variable is a characteristic of a person, object or phenomenon that can take on different values.

Types of Variable in Biostatistics

Variable in biostatistics can be classified into:

1. Categorical or Qualitative Variable and Numerical (Quantitative) Variable.
2. Independent and Dependent Variable.
3. Confounding Variable.
4. Continuous and Discrete Variable.

1. Numerical and Categorical variables

• Numerical Variable: this variable is also known as quantitative variable. Numerical variable is the values of variables which are expressed in numbers. For instance, person's age (measuring in year), weight (expressed in kilograms), distance between residence and hospital (expressed in kilometers or in miles), monthly income (expressed in dollor).
• Categorical Variable: this variable is also called qualitative variable or attributes. it is the values of variables which are expressed in categories. E.g. sex (male or female), nation (USA, Somalia, Uganda), Religion (Muslim or Christian), colour of the eye or skin (red, black, blue). 

2. Independent and Dependent Variable.

• The variable that is used to describe or measure the problem under the study is called dependent variable.
• the variable that is used to describe or measure the factors that are assumed to cause or to influence the problem is called independent variable.

For instance, cigarette smoking may cause lung cancer.

here cigarette smoking is independent variable while lung cancer is dependent variable.

Another example, if you say lung cancer may cause death, the lung cancer will be independent variable and death will be dependent variable.

3. Confounding Variable

It is the variable that is associated with the problem and with a possible cause of problem.

E.g. if high consumption of alcohol (independent variable) causes esophageal cancer (dependent variable), the cigarette smoking is the associated factor or confounding factor of lung cancer.

4. Continuous and Discrete Variable

• Continuous Variable: it is variable which can have an infinite numbers of possible values in a given interval. E.g. Height in meter or centimeter, weight in kilogram or grams.
• Discrete Variable: it is variable which can have only a finite numbers of values in a given interval. E.g. Number of beds in hospital, number of members in a family, number of population in a community.

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