Data collected from various experiments does not lead to any information by itself. Hence it should be complied, classified and presented in a purposive manner to bring out important points clearly and strikingly, therefore, the manner in which statistical data is presented is of utmost importance.
Charts and Diagrams Based on the data type, representation of data also differs. There are two different data types in statistics; they are: (i) discrete, and (ii) continuous type of data.
i) Discrete data are distinct and separate and also invariably whole numbers, e.g. no of deaths due to particular disease. ii) Continuous data are those, which takes the value bettewn range of values, e.g. height, weight, age etc.
Presenting data in charts and diagrams is useful in simplifying the presentation and enhancing comprehension of the data. Representation of data in these forms provides the following:
They simplify the complexity.
They facilitate visual comparison of data.
They arouse the interest in reader.
They save time and labour.
They draw some conclusion directly or indirectly.
Charts and diagrammes for discrete data
Bar chars: These are merely a way of presenting a set of numbers by the length of a bar; the length of the bar is proportional to the magnitude to be represented. Bar charts are easy to prepare, easy to understand and enables visual comparison. There are three types of bar chart; they are: (i) simple bar chart, (ii) multiple bar chart, and (iii) compound (or compenent or stacked) bar chart.
Simple bar chart
Multiple bar chart
Component bar chart
Pie chart: Here instead of comparing the length of a bar, the areas of segments of a circle are compared. The area of each segment depends upon the percentage, which is converted to angle and drawn.
Pictogram: These diagrammes are used for a laymen those who cannot understand technical charts like bar charts. Here pictures or symbols are used to present the data.
Charts and diagrammes for continuous data
Histogram:Histogram is a set of vertical bars whose areas are proportional to the frequencies represented. The class intervals are given along the horizontal axis and the frequencies along the vertical axis.
Frequency polygon: A frequency polygon is a graphical display of a frequency table. The intervals are shown on the X-axis and the number of scores in each interval is represented by the height of a point located above the middle of the interval. The points are connected so that together with the X-axis they form a polygon.