Reading Graphs and Charts

Reading Graphs and Charts

• are more attractive and easy to understand than tables

• enable the reader to ‘see’ patterns in the data• are easy to use for comparisons and analysis• allow information to be presented in various

ways using different types of charts allow for special designs like demographic pyramids and thematic maps

Charts and graphs have the following advantages. They:


The main purpose of charts or graphs is to visually impart information that cannot be easily read and interpreted from a table of data.

it can be sometimes difficult to ’see’ patterns, trends and contrasts in a table that has many data points. using charts can be a good method of showing trends and changes in statistical data.

Charts can also be used to make predictions and forecasts, and to compare two or more data sets.


Basic components of a chart

• Title

• Axis labels (including the units of measurement), Tick marks on the axes (with labels for some tick marks and subgroups)

• footnotes and references to the source data.


An effective chart also has the following characteristics

• Clear objective and key messages to be presented

• Good choice of graph type for the information that is to be presented

• Appropriate level of simplicity or complexity, depending on the readers’ abilities to analyse, interpret and understand


Types of chart

• Pie chart• Line chart• Bar chart• Area chart• Scatter plot

Pie chart

Pie charts are useful for illustrating percentage distributions of components within a total and are therefore suitable for presenting overviews of data.

The area of each slice of the pie is proportional to the relative share, or frequency, of each item that makes up the total

Pie chart

Pie chart

The pie chart however is not suitable for displaying data with a high degree of accuracy.

This is especially true when an item represents a very small share of the total, in which case its slice may be very thin and difficult to measure.

it can also be difficult to see the difference between two items with similar but slightly different shares of the total. it is usually necessary to clearly label the value of each slice of the pie in order to overcome this limitation.

Line graph

A simple way to show time-series or trends.

A single graph can display multiple lines, with one line for each data series or sub-population, such as the number of students by sex.

Horizontal grid- lines make it easier for the eye to follow the plotted lines, to identify the data values along the data series, and to get a clearer picture of the trend and changes in the values for different data series.

Line graph

Bar chart

• A bar chart displays data as rectangular bars with lengths proportional to the values that they represent.

• Bar charts are useful for comparing two or more values, such as the gross enrolment ratios by sex and region in a region.

• The bars can be vertically or horizontally oriented Horizontal bar charts are often used when there are many bars and each bar requires a long label, which would overlap or be truncated in vertical bar charts

Bar chart

Area graph

• Area graphs are an alternative to the stacked bar chart.

• An area graph is created by drawing lines to connect the values of component data series, and then stack them one on top of another.

• Area graphs are particularly effective for showing changes in total (and component) values over time.

• When designing an area graph, make sure that the time scale is drawn correctly, using a linear scale for the time points

Area graph

Scatter-plot

Scatter plots are used for showing the relationship between two variables, or data series, by plotting pairs of values.

Time-series data

• Sometimes, it is needed to present information about changes over time.

• To present time-series data, summary tables and charts can be used to effectively show changes in values from one time period to the next in chronological order.

• As long as the definition of the data and the collection methods were consistent over time, tables and charts can be used to study past trends and estimate future values.

Time-series data

Frequency histogram and polygon

The frequency histogram is like a column graph without the spaces between columns.

The frequency polygon is a special line graph used in statistics.

These graphs can be drawn separately or combined.

The information in a frequency distribution table can be used to draw these graphs.


The frequency polygon is drawn on axes the same as the histogram – the scores on the horizontal axis and the frequency on the vertical axis.


When both the frequency histogram and polygon are drawn on the same axes they look like this:

The area under the polygon is the same as the area of the histogram.


Misleading graphs

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Misleading graphs


Misleading graphs

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Misleading graphs


Misleading graphs

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Misleading graphs


Misleading graphs

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Misleading graphs

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For graph axis not starting from zero


Misleading graphs

Changing the y-axis maximum affects how the graph appears. A higher maximum will cause the graph to appear to have less-volatility, less-growth and a less steep line than a lower maximum.

Changing y-axis maximum 6


Misleading graphs

Changing the ratio of a graph's dimensions will affect how the graph appears.

Changing ratio of graph dimensions

Reading Graphs and Charts

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