Here’s a table that summarizes the types of variables: Show
There are 2 basic types of variables: quantitative and qualitative. 1. Quantitative or Numerical variable:A quantitative or Numerical variable is a type of variable consisting of values that represent counts or measurements of a certain quantity. For instance, age, height, number of cigarettes smoked, etc. A quantitative variable can be either continuous or discrete. 1.1. Continuous variable:A continuous variable is a type of quantitative variable consisting of numerical values that can be measured but not counted, because there are infinitely many values between 1 measurement and another. Example: Cholesterol level measured in mg/dl. 1.2. Discrete variable:A discrete variable is a type of quantitative variable consisting of numerical values that can be measured and counted, because these values are separate or distinct. Unlike a continuous variable, if you select a value at random from a discrete variable, there is a concept of next and/or previous value. Example: Vote count in an election. A discrete variable may take on an infinite number of values as long as they are countable (even if we would be counting forever). For instance, the “number of dice rolls until we get 2 consecutive sixes” is a discrete variable because it is countable, although we could theoretically go on forever without getting 2 sixes in a row. ⚠ Transforming text into discrete variables: In practice, all continuous variables are discrete! Since the precision of our measurements is not infinite, a theoretically continuous variable will practically be discrete i.e. it will only take on distinct values, although very close to one another. However, for the purpose of analyzing data, we consider a variable continuous if it can take on a very large number of possible values within a certain interval such that it would be practically impossible for 2 observations to have the same value – in other words, within a given interval, the possible values that a continuous variable can take do not have to be literally infinite. Here are some examples to help you differentiate between discrete and continuous variables: Exercise: Discrete or continuous?– Is age discrete or continuous?Age is a discrete variable when counted in years, for example when you ask someone about their age in a questionnaire. Age is a continuous variable when measured with high precision, for example when calculated from the exact date of birth. – Is mass discrete or continuous?Mass is a continuous variable since it can take on any value between its minimum and maximum. Mass is not discrete since there is no definite answer to the question: What is the next value for mass after, for example, 63.207 Kg? – Is shoe size discrete or continuous?Shoe size is a discrete variable since it takes on distinct values such as {5, 5.5, 6, 6.5, etc.}. Because there is a finite number of values between any 2 shoe sizes, we can answer the question: What is the next value for shoe size after, for example 5.5? The answer is 6 – making it a discrete variable. – Is dosage of medicine discrete or continuous?Dosage of medicine is a discrete variable if the medicine is administered as distinct doses of 5, 10, and 20 mg for example. Dosage of medicine is a continuous variable if the medicine is administered as a constant-rate intravenous infusion. – Is systolic blood pressure discrete or continuous?Theoretically, the systolic blood pressure of an individual is a continuous variable since it can take on any value between 0 and 300 mmHg. Practically, the systolic blood pressure as measured by a monitor is a discrete variable since it can only take on distinct values, such as: 140 mmHg, 141 mmHg, etc. ⚠ Half continuous and half discrete variables: 2. Qualitative or Categorical variable:A qualitative or categorical variable is a type of variable consisting of text characters or labels that describe groups of observations. For instance, gender, marital status, stages of a disease, etc. ⚠ Numbers representing categorical data:
A qualitative variable can be either ordinal or nominal. 2.1. Ordinal variable:An ordinal variable is a type of qualitative variable consisting of text or labels that have a logical order, i.e. one category represents more or less of the other, but taking the difference between categories or their average is meaningless. Example: Hypertension stages. 2.2. Nominal variable:A nominal variable is a type of qualitative variable consisting of text or labels that have no logical order. Example: Gender. Summary: A decision tree for identifying variable typeReferences
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