Even if the primary aim of a study involves inferential statistics, descriptive statistics are still used to give a general summary. Descriptive statistics give a summary about the sample being studied without drawing any inferences based on probability theory. Statistics can be broadly divided into descriptive statistics and inferential statistics. A control variable is a variable that must be kept constant during the course of an experiment. For example, in a clinical trial for a topical treatment in psoriasis, the concomitant use of moisturizers might be a confounding variable. They are linked with dependent and independent variables and can cause spurious association. Confounding variables are extra variables, which can have an effect on the experiment. Other terms sometimes used synonymously include blocking variable, covariate, or predictor variable. The independent variable (sometime also called explanatory variable) is something which is not affected by the experiment itself but which can be manipulated to affect the dependent variable. For example, in a clinical trial on psoriasis, the PASI (psoriasis area severity index) would possibly be one dependent variable. In the context of an experimental study, the dependent variable (also called outcome variable) is directly linked to the primary outcome of the study. Variables can be classified into various ways as discussed below. For a variable to be “good,” it needs to have some properties such as good reliability and validity, low bias, feasibility/practicality, low cost, objectivity, clarity, and acceptance. For example, if you want to do an experiment based on the severity of urticaria, one option would be to measure the severity using a scale to grade severity of itching. The importance of variables is that they help in operationalization of concepts for data collection. Variables either are the primary quantities of interest or act as practical substitutes for the same.
It is a feature of a member of a given sample or population, which is unique, and can differ in quantity or quantity from another member of the same sample or population. A variable is an essential component of any statistical data. What is a variable? To put it in very simple terms, a variable is an entity whose value varies.
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