Types and Data Pretreatment

It is expedient to distinguish the variables on the basis of three scales nominal, ordinal, and numeric. 

The ordinal scales are also qualitative, but they can rank (order) the items measured in terms of which has less and which has more of the quality represented by the variable, but still they do not allow us to say how much more. A typical example of an ordinal variable is the toxicity A compound can be classified as highly toxic, moderately toxic, hardly toxic, or nontoxic. Although the compounds can be ordered according to the toxicity, how much more toxic they are caimot be established. The ordinal scale provides more information than nominal scale, but how much more caimot be established. 

The numerical scale is quantitative in nature. This scale of measurement allows us not only to rank the items that are measured but also to quantify and compare the sizes of differences between them. Some authors distinguish interval and ratio scales, whether an absolute zero point is defined or not, but this is not mandatory. For example, the temperature measured in Celsius is on an interval scale, whereas in Kelvin it is on a ratio scale. Interval scales do not have the ratio property. 

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