Data and Representation

Statistics is a branch of Mathematics which deals with collection, presentation, analysis, interpretation of data and drawing inferences and conclusions there from.

Data: Facts or figures, which are numerical or otherwise collected with a definite purpose.

Types of Data

  1. Primary Data: Data which an investigator collects for the first time for his own purpose.
  2. Secondary Data: Data which the investigator obtains from some other source, agency or office for his own purpose.

Presentation of Data

  1. Raw or Ungrouped Data: The data obtained in original form and presented ungrouped without any re-arrangement or condensed form.
  2. An Array: The Presentation of a data in ascending or descending order of magnitude.
  3. Grouped Data: Rearrangement or condensed form of data into classes or groups.

Range of Data: Difference between the highest and lowest values in the data.

Frequency: The number of times an observation occurs in data.

Class Interval: Each group in which the observations or values of a data are condensed.

Class limits: Values by which each class interval is bounded. Value on the left is called lower limit and value on the right is called upper limit.

Class size: Difference between the upper limit and the lower limit.

Class mark of a class interval: Mid value of a class interval = (lower limit + upper limit)/2

Cumulative Frequency of a class: Total of frequencies of a particular class and of all classes prior to that class.

Graphical Representation of Data

  1. Bar Graph: A pictorial representation of data in which usually bars of uniform width are drawn with equal spacing between them on one axis and values of variable (frequencies) are shown on other axis.
  2. Histogram: A pictorial representation like bar graph with no space between the bars. It is used for continuous grouped frequency distribution.
  3. Frequency Polygon: A graphical representation of grouped frequency distribution in which the values of the frequencies are marked against the class mark of the intervals and the points are joined by line segments.