Tools Used in Statistics : Graphs , Charts, Pictograms and Histograms

Bar Graphs

It is a chart with rectangular bars with lengths proportional to the values that they represent.

external image gr2bargraph3d.jpg

  • Usually, the y-axis (vertical) shows the quantity and the x-axis (horizontal) shows the time.
  • It is very useful as you can compare several kinds of subjects at different times. (uses different colours to represent different subjects)
  • When interpreting a bar graph, you will need a ruler to get the correct value. Do NOT estimate the value.
  • Draw dotted lines when need or write down the values of each bar when interpreting a bar graph. These are useful tips to get accurate measurements.
  • It shows comparison of subjects at different times, which mkes it useful to detect trends.


It is an ideogram that conveys its meaning through to physical objects, but it is not accurate in showing exact numbers.


  • It is useful as it allows quick comparisons of different categories.
  • Each subject (unit) can represents a certain quantity. (i.e. A picture of a basketball is equal to 5 basketballs)
  • However, it is troublesome as the exact quantity is not given and calculation is needed to achieve the exact amount


It is a vertical bar graph with no space in between the bars.

external image img140.jpeg

  • The y-axis determines the frequency, whereas the x-axis determines the quantity of the subject.
  • The frequency refers to how numbers fall into that certain range (look at the examples if you are unsure about this part)
  • The bars of a histogram must touch each other as the numbers are grouped to form a continuous range from left to right
  • It is different from a bar graph as the bar graph shows the frequency of each items on a set of data, but a histogram shows the set of data which was grouped and arrange to display in continuous manner.
  • It is useful in detecting the trend.

Pie Charts

It is a circle that is divided into different sectors and each sectors correspond to the percentage of each category.

external image blog-earnings-pie-chart.jpg
  • The angle of each sectors is propotional to its actual value and the angle can be easily found.
  • Different colours are used to represent different subjects. The legend is written beside the pie chart.
  • It is very useful as it uses percentage instead of actual numbers, which makes it easier to compare.
  • It can be difficult to interpret if there are too many sectors.
  • If the percentage is not given for each sector, a protractor will be needed to find the angles and percentage for each sector.
  • It is very useful, yet time-consuming.

Line Graphs

It is a graph that is obtained by plotting the points corresponding to the data and then joining the points.

external image commom_line_graph.jpg

  • It is suitable to show a rising or falling trend in a set of data over a period of time.
  • The x-axis usually shows the period of time, whereas the y-axis shows the quantity.
  • When using line graphs in statistics, it is usually to present a research over a long period of time. (i.e. human population over the years, sales over the months)
  • It is difficult to get the exact quantity as it is used to show the trend instead of the actual values
  • A ruler is also needed to be more accurate to get the value.

Look at the examples to get a clearer overview of these tools.