Introduction

What is data, information and how the data is collected and organized to get a good piece of information are introduced in as simplest as possible in this chapter Data Collection and Organization.

In statistics, data handling is a way of collecting, organising, presenting the data on charts or graphs and how to read and interpret the graphs. After data collection, data is organised using tables.

Data can be represented in different ways such as pictograph, bar graph, line graph, histogram, tables, tally charts etc.

AS we already know the ways of collecting and organising the data, now we move on to presenting them on graphs and charts.

Presentation of data

Once the data is organised into table, that will be ready for the presentation on charts and graphs. The benefit of presenting the data onto charts and graphs is that the data can be visually compared better than the tables.
Below are the types of graphs and charts that are used commonly like pictograph, bar graph, double bar graph, histogram, pie charts and line graphs. Let’s have a look next at them with examples.

Pictograph

In pictographs data is represented using pictures or symbols, it is called pictograph. A picture or a symbol is selected for a value then it is plotted onto graphs.

Bar graph (Column graph)

Bar graph is also known as bar chart or column graphs. Bar graph uses bars to represent the data. These bars can be in vertical or horizontal position.

Types of bar graph

Depending upon the position of bar in bar graph, it is of two types vertical bar graph and horizontal bar graph.

Vertical bar graph

The bar graph which have vertical bars is called as vertical bar chart.

Horizontal bar graph

The bar graph which have horizontal bars is called as horizontal bar chart.

Steps to draw bar graph

1. Draw two perpendicular lines, i.e. one vertical and other is horizontal. These perpendicular lines are called vertical axis and horizontal axis also. These both axis will represent the data that from the table that need to be drawn on the graph.
2. Mark the vertical and horizontal axis by names from the table column names.
3. Draw bars for each observation from the table and keep all bars in a graph of same width always. The gap between two bars should always be kept same.
4. Choose suitable scale along vertical line.

These steps work to draw both types of bar graphs vertical and horizontal.

Some important things to keep in mind while making a bar graph are: The width of all bars in a bar graph are kept same.
The space between all bars in a graph must be equal.
The height of each bar represent the numerical value of data.

So, let’s see next how to draw a bar graph using the following table which has the sale of different items sold at grocery shop on different days.

Double bar graph

As the name suggests, double bar graphs have two bars on the graph unlike a bar graph, which has only one bar. The purpose of two bars in double bar graph is to make comparison between two sets of data.

Steps to make a double graph are all same as of bar graph. The only difference lies in number of bars. Doubl bar graph will use two bars from two columns of numerical data from a table.

Pie Graph or Pie Chart

Pie graph is also a pictorial representation of numerical data, represented by sectors of circle.
Pie graph consists of circle and circle is divided into as many sectors as there are quantitys of data. The area of each sector is proportional to quantity it represents.
A pie graph is used to compare parts of whole and the circle represents the whole. Some steps need to be followed to represent the data into pie graph.

Steps to draw pie graph

1. From the given data, find the sum of all given quantities.
2. Divide the each given quantity by sum obtained in step 1 and multiply it by 360⁰ to get the value of a sector angle or central angle.
   Central angle = \(\frac{value \;of\; given\; quantity}{sum \;of \;all\; given\; quantities} \times 360\)
3. Draw a circle of any radius.
4. Construct the various sectors corresponding to its central angle in clockwise direction.
5. Put explanatory or descriptive labels inside each sector.

To construct the pie graph, we need to find central angle corresponding to given quantity.

Central angle of given quantity = \(\frac{value\; of\; quantity}{sum \;of\; all\; quantity\; values} \times 360\)

The following example shows the expenditure of a person on different items during a month.

Line graph

Line chart ot line graph is known as curve chart. Line graph displays the data that changes continuously over periods of time. In this chart, data diaplays as series of data points which is called as markers. There data points are connected by time segments. A time chart is used to analyse the travel in data over specific interval of time.