For the sleep deprivation study, the null hypothesis would be that sleep deprivation has no effect on performance. Variables A variable is any measured characteristic or attribute that differs for different subjects. For example, if the weight of 30 subjects were measured, then weight would be a variable. The first step, before any calculations or plotting of data , is to decide what type of data one is dealing with. Because qualitative data always have a limited number of alternative values, such variables are also described as discrete.
All qualitative data are discrete, while some numeric data are discrete and some are continuous.
For statistical analysis, qualitative data can be converted into discrete numeric data by simply counting the different values that appear. A random variable is a variable in the mathematical sense, but one that takes different values according to a probability distribution. In Statistics, we use random variables to build probability models for data variables. This makes sense because when data are collected on observational units sampled at random, the values recorded for the data variables can be regarded as realisations of mathematical random variables. Qualitative Data Qualitative data arise when the observations fall into separate distinct categories.