11.3 Sketching A Bar Chart For A Given Set of Biological Data

Introduction

Biostatistical data is usually recorded in the form of tables and figures. However, large amounts of numerical data in tables are not easy to understand at a glance. Diagrams, graphs, and charts provide a clearer and more attractive way of presenting data. A bar chart is one of the most common and simple ways to display biological data. This topic explains the need for graphic presentation, the parts of a bar chart, and the steps to sketch one.

Definition

Bar chart (bar graph): A graph that uses bars of equal width but variable length (or height) to represent data. The length or height of each bar represents the magnitude of a quantity or value.

Main Idea

Biostatistical values (data) are documented in the form of figures and are usually recorded in the form of tables. But numerical or arithmetical figures are usually not attractive. Large number of figures in tables are not easily understandable. It seems difficult to get a clear picture from the numerical data.

Diagrams and graphs are comparatively more attractive way of presenting the clear and complete picture of data. Moreover, data information presented in the form of diagrams, pictures, charts and graphs leave long lasting impression on the mind of the observer.

Multiple types of graphs, pictures and diagrams are used in representing data including bar-chart, rectangles and pie-chart.

Core Concept

Need and Importance of Graphic Presentation

Simple Bar Diagram or Simple Bar Chart

Detailed Explanation

1. Why Graphical Presentation is Important

Biostatistical values (data) are documented in the form of figures and are usually recorded in the form of tables. But numerical or arithmetical figures are usually not attractive. Large number of figures in tables are not easily understandable. It seems difficult to get a clear picture from the numerical data.

Simple explanation: Tables of numbers are hard to understand quickly. Graphs and charts make data easier to understand.

Advantages of graphical presentation:

• Diagrams and graphs are comparatively more attractive.
• They present a clear and complete picture of data.
• They leave a long-lasting impression on the mind of the observer.
• They make it easier to compare values.

Types of graphs:

• Bar chart
• Rectangles
• Pie chart

2. What is a Simple Bar Chart?

Simple bar chart have bars which are drawn to represent a single data without further classification of the characteristics.

Key features:

• Bar chart represent only one characteristic of the data.
• One bar represents only one value or figure.
• There may be multiple bars representing many values or figures.
• In a simple bar chart, bars of equal width are drawn, but their lengths are variable.
• Heights or length of the bars represent the magnitude of a quantity or degree of value in the data.

Simple explanation: A bar chart uses bars to show data. Each bar represents one value. The height or length of the bar shows how big the value is.

3. Sketching or Construction of Bar Graphs or Bar Charts

Some basic steps in sketching of bar charts are:

Important note: Bars in the graph may be drawn vertically or horizontally but normally vertical bars are used.

Simple explanation: To draw a bar chart:

• Use graph paper.
• Draw X-axis (horizontal) and Y-axis (vertical).
• Label the X-axis with data items.
• Choose a scale for the Y-axis.
• Draw bars of equal width but different heights.

4. Example: Bar Chart for Bt Cotton Varieties

Example 1: Draw simple bar graph/chart to represent the cotton (weight in Kgs) produced per acre of land from five Bt cotton varieties (IR-NIBGE-370, RH-647, MNH-886, FH-142, IUB-2013 and FH-Lalazar) in year 2023.

Data table:

Steps to sketch the bar chart:

• Take graph paper.
• Draw X-axis (horizontal) and Y-axis (vertical) intersecting at zero.
• Label X-axis with the names of Bt cotton varieties.
• Choose a suitable scale for Y-axis (e.g., 1 cm = 200 Kg).
• Draw bars of equal width for each variety.
• Height of each bar corresponds to the cotton production.

Simple explanation: The bar chart will show the cotton production of each variety. The tallest bar represents the highest production (FH-142 = 2000 Kg), and the shortest bar represents the lowest production (IR-NIBGE-370 = 1200 Kg).

Summary Table

Intermediate Level

A bar chart is a graph that uses bars of equal width but variable length (or height) to represent data.

Key features:

• Represents one characteristic of data.
• One bar = one value.
• Equal width, variable height.
• Height represents magnitude.

Steps for sketching:

• Take graph paper.
• Draw X-axis and Y-axis.
• Label X-axis with data items.
• Choose uniform width and gap for bars.
• Choose a suitable scale for Y-axis.
• Label Y-axis with units.
• Calculate heights and mark dots.
• Draw bars carefully.
• Recheck all entries.

Key points:

• Bars are usually drawn vertically.
• Bar charts are useful for comparing values.
• They leave a long-lasting impression.

Important Points

• - Biostatistical values (data) are documented in the form figures and are usually recorded in the form of tables.
• - But numerical or arithmetical figures are usually not attractive.
• - Large number of figures in tables are not easily understandable.
• - It seems difficult to get a clear picture from the numerical data.
• - Diagrams and graphs are comparatively more attractive way of presenting the clear and complete picture of data.
• - Moreover, data information presented in the form of diagrams, pictures, charts and graphs leave long lasting impression on the mind of the observer.
• - Multiple types of graphs, pictures and diagrams are used in representing data including bar-chart, rectangles and pie-chart.
• - Simple bar chart have bars which are drawn to represent a single data without further classification of the characteristics.
• - Bar chart represent only one characteristic of the data.
• - One bar represents only one value or figure and there may be multiple bars representing many values or figures.
• - In a simple bar chart, bars of equal width are drawn, but their lengths are variable.
• - Heights of length of the bars represent the magnitude of a quantity or degree of value in the data.
• - Some basic steps in sketching of bar charts are:
• 1. Take a graph paper with suitable sizes and scales as per requirement and type of data.
• 2. Draw two lines on the graph, perpendicular to each other and intersecting at zero.
• 3. Label the axis of the graph, horizontal line is X-axis and vertical line is Y-axis.
• 4. Choose uniform width of bars and uniform gap between the bars along the horizontal axis (X-axis).
• 5. Label X-axis with the names of the data items whose values are to be presented.
• 6. Choose a suitable scale to determine and specify the heights of the bars for the given values along the vertical axis (Y-axis).
• 7. Label the Y-axis scale with specific unit of data value to grade the length of bars.
• 8. Calculate the heights of the bars according to the scale chosen and mark as dots.
• 9. Draw the bars carefully and recheck all the entries.
• - Bars in the graph may be drawn vertically or horizontally but normally vertical bars are used.

Remember

• - Bar chart = graph using bars
• - Equal width, variable height
• - Represents magnitude of a quantity
• - X-axis = horizontal; Y-axis = vertical
• - Steps = 9 steps for sketching
• - Bars usually drawn vertically
• - Bar charts are attractive and easy to understand
• - Useful for comparing values

Common Mistakes

• 1. Forgetting to label the axes.
• - X-axis and Y-axis must be labeled.
• 2. Using unequal width of bars.
• - Bars must be of equal width.
• 3. Not choosing a suitable scale.
• - The scale should be appropriate for the data.
• 4. Forgetting to leave uniform gaps between bars.
• - Gaps between bars should be uniform.
• 5. Mixing up X-axis and Y-axis.
• - X-axis = horizontal; Y-axis = vertical.
• 6. Not rechecking the entries.
• - Always recheck the bars and labels.
• 7. Thinking bar charts can only be vertical.
• - Bars can be vertical or horizontal, but vertical is more common.

Quick Revision

60-Second Revision

• Bar chart = graph using bars
• Equal width, variable height
• Represents magnitude of a quantity
• X-axis = horizontal; Y-axis = vertical
• Steps = 9 steps for sketching
• Bars usually drawn vertically
• Bar charts are attractive and easy to understand
• Useful for comparing values
• Warning: Do not forget to label the axes. Bars must be of equal width. Choose a suitable scale for the Y-axis.