Different types of

variables

Issues to cover – in a flash

1. Quantitative variable (numeric variables)– 1.1 Discrete variable– 1.2 Continuous variable

2. Qualitative variable (Categorical variable)– 2.1 Nominal variable– 2.2 Binary variable– 2.3 Ordinal variable

TYPES OF VARIABLES

• QUALITATIVE VERSUS QUANTITATIVE

• CONTINUOUS VERSUS DISCRETE

• NOMINAL, ORDINAL, INTERVAL, RATIO

• DEPENDENT VERSUS INDEPENDENT

• EXPOSURE VERSUS OUTCOME

• HIGHLY CONFUSING!!!

VARIABLES

QUALITATIVE QUANTITATIVE

CONTINUOUS DISCRETE

1. Quantitative variable

1.1 Discrete variable: A variable which can only take certain values, usually whole numbers (a count)

– Examples number of visits to a doctor, number of asthma episodes in a year, number of children in a household etc.

1.2 Continuous variable: a variable which can theoretically take any value within a given range

– Examples: height, body mass index etc.

2. Qualitative variable(Categorical variable)

• A variable whose values are represented by names or labels of the same characteristic. Examples are ethnicity, blood group, eye colour, nationality.

• All qualitative variables are discrete

2.1 Nominal variable(Categorical variable)

• Categorical variables where the categories are not ordered in increasing or decreasing quality or intensity.

E.g. Hair colour

Other examples?

2.2 Binary variable

• A categorical variable which takes only two categories or possible values.

– Examples: Yes/No, Dead/Alive, Positive/Negative

Other examples?

2.3. Ordinal variable

• A categorical variable in which the different levels of the variable are ordered. Successive levels represent “increases” or “decreases” in the characteristic conveyed by the variable.

Examples: – Severity of pain: no pain, minimal pain, moderate pain,

severe pain– Grades of malnutrition categorized by BMI (Mild, moderate

and severe)

Ordinal variables

• It is important to analyse this type of data with special methods

• E.g. chi square for trend, Kruskal-Wallis test (non-parametric significance test) and not with methods used for nominal variables