There are two kinds of statistical variables. These are quantitative and qualitative variables. A quantitative variable is finite and computable. A quantitative variable can be measured on an ordinal, interval or on a ratio-scale. A qualitative variable cannot be measured. These variables are only classified on the basis of their distinct attributes. For example, the number of tomatoes in the refrigerator is a quantitative variable. The different types of vegetables in the refrigerator are qualitative. The analyst must exercise caution in classifying the variables.
Categorize your variable. Different statistical studies have different types of variables. A study on the monthly consumption of tissue paper by households would have different variables than a study on preference for soap brands. The variables of the study must be defined as coherently and logically as possible.
Classify all the items you have in the categories created. This is possible only for quantitative items. For example, if you are television manufacturing company; first categorize your sales by months and then measure the volume of sales in each month. You may rank or order the data you have. It is possible to classify only numerical values. Qualitative aspects like the color of the product or other physical attributes do not have numerical values.
Sort your variables into quantitative and qualitative categories. Every statistical study has both qualitative and quantitative elements. Carefully use the variables. For example, the popularity of a laptop may be due to the screen size. This is a qualitative aspect of the study. The demand for the laptops could vary during different months. This is a quantitative aspect of the study.