Statistics deals with the aggregates. An individual, to a statistician has no significance except the fact that it is a part of the aggregate.
Statistics is concerned with quantitative data. However, qualitative data also can be converted to quantitative data by providing a numerical description to the corresponding qualitative data.
The theory of statistical inferences is built upon random sampling. If the rules for random sampling are not strictly adhered to, the conclusion drawn on the basis of these unrepresentative samples would be erroneous.
We can broadly classify data as
Mode of Presentation of Data
(a) Textual presentation;
(b) Tabular presentation or Tabulation;
(c) Diagrammatic representation.
The types of diagrams:
(a) Line diagram or Historiagram;
(b) Bar diagram;
(c) Pie chart.
Frequency Distribution of a Variable
(a) Find the largest and smallest observations and obtain the difference between them, known as Range, in case of a continuous variable.
(b) Form a number of classes depending on the number of isolated values assumed by a discrete variable. In case of a continuous variable, find the number of class intervals using the relation, No. of class Interval X class length≅Range.
(c) Present the class or class interval in a table known as frequency distribution table.
(d) Apply ‘tally mark’ i.e. a stroke against the occurrence of a particulars value in a class or class interval.
(e) Count the tally marks and present these numbers in the next column, known as frequency column, and finally check whether the total of all these class frequencies tally with thetotal number of observations.