© SSER Ltd. How Science Works Types of Graph

This presentation looks at the following types of graph: 1.Bar Chart 3.Line Graph4.Pie Chart 5.Scatter Graph Presenting Data 2.Histogram 6.Kite Diagram 7.Rose Diagram Having carried out your investigation, you will need to give careful thought as to how you are going to present the data. There are a variety of ways to present data and you must select the most appropriate way for the data you have collected.

 The gap between the columns makes it easy to distinguish between the separate categories. Bar Chart A bar chart is used to display categorical (qualitative) data, e.g. favourite colours, names of river, type of vehicle.  All the columns have the same width, but the width of the columns has no meaning.  The ‘labels’ on the x-axis should be written centrally under the bars.

Bar Chart There is often no natural order for the columns, so it can be helpful to arrange them in order of descending frequency.

A multiple bar chart is useful for comparing different, yet related groups of data, e.g. data from different years. Multiple Bar Chart

A compound bar chart splits the bars into further categories. Compound Bar Chart

Histogram (In Maths, this is called a frequency chart or frequency diagram - A mathematical histogram looks very similar but has frequency density on the vertical column, not frequency.) A histogram looks like a bar chart, but shows the frequency for grouped data. A histogram has no gaps between the columns.  The x-axis is either a continuous scale or a sequence of consecutive intervals. Intervals should be written centrally under the columns.  A histogram uses frequency on the y-axis. Frequency is indicated by the height on the vertical scale.  The columns (and therefore the group intervals) must be of equal width.

Histogram A histogram with a continuous scale on the x-axis...

Histogram A histogram with a sequence of consecutive intervals on the x-axis...

A line graph is used to display quantitative data, e.g. temperature, electrical current or population. Line Graph When drawing a line graph, the points may joined by a straight line. However, when displaying results from experiments, it is sometimes appropriate to draw a ‘line of best fit’ - a curve which is a better indication of the overall trend in the data. This also helps to identify possible errors in measurement, since an error may be a long way from the ‘line of best fit’.

Line Graph

The Use of Error Bars The error bars indicate the maximum and minimum readings, and give an indication of the consistency achieved. The mean of the readings can be plotted to draw the line graph. The highest and lowest reading at any point can be shown using error bars. When carrying out an experiment, it is common to take 3 or more readings of the dependent variable for each value of the independent variable. Error bars also help to show anomalous results, e.g. if one error bar is particularly large, it may indicate that something has gone wrong with the measuring at that point, or that something changed in the experiment, e.g. did someone turn up the bunsen?

The Use of Error Bars Small error bars across the graph indicate that readings were taken consistently.

Pie Chart A pie chart is drawn to show how the total frequency is divided up between the possible values of categorical, or grouped data. It shows the relative proportions of each value of the variable. Pie Chart to Show the Heat Loss from a Typical UK House

Pie Chart  The angle at the centre of the sector should be proportional to the frequency for that particular category.  Each sector should be coloured or shaded to distinguish it from others. The category name should be written on the sector or beside it. If colouring alone is used to identify the sectors, then a key should be provided.  The percentage for each sector should be written clearly on the pie chart, either with the label or on the sector of the pie chart. In a pie chart...

Scatter Graph A scatter graph is used to show an association between two variables, such as height and weight.

Data in scatter graphs is plotted as a pair of co-ordinates, e.g. a single piece of data might be (164cm, 45kg). If the majority of the points form an elliptical shape, a ‘line of best fit’ is drawn, roughly between the centre of the points, usually having an equal number of points above and below the line. The line of best fit may pass through some points but it does not join up points as in a line graph. It is then used to assess the correlation between the data, and to predict the value of one variable from another. Scatter Graph The line of best fit on a scatter graph is always a straight line.

If the line of best fit points upwards from bottom left to top right, then we say that a positive correlation exists between the two variables... Scatter Graph

If the line of best fit points downwards from top left to bottom right then we say that a negative correlation exists between the two variables... Scatter Graph

If there is no clear pattern between the plotted points, then we say that there is no correlation between the two variables...

Kite Diagrams A kite diagram is commonly used to display the distribution of animals and plants down a shoreline. The data plotted is usually an abundance scale (1-5) or % cover of a quadrat.

There can be gaps in the distribution of a species, e.g. this can be due to sandy outcrops amongst rocks as is the case for F. spiralis in the above chart. Therefore, care must be taken when interpreting kite diagrams – but they are good at showing zonation. Kite Diagrams The data is plotted on both sides of a median line - thus kite diagrams always have a symmetrical aspect. The y-axis shows distance from a fixed reference, e.g. low water mark. Lower shore showing Laminaria distribution

The bars usually do not extend to the origin (centre) of the radial y-axis as the ‘hole’ is needed to prevent their overlap. Two or more sets of data can be displayed as in a compound bar chart. Rose Diagrams A rose diagram is commonly used for cyclic data, e.g. in situations where the day, month, year or compass bearings are of importance. The data can be grouped or categorical. In Diagram 1 the data is related to compass bearings and in Diagram 2 it is related to the month of the year. Diagram 1Diagram 2

Rose Diagrams Prevailing wind directions An example of the use of rose diagrams is in the biological monitoring of air pollution. A study of the prevailing wind directions can help identify the source of any pollution. Lichen grow on certain tree trunks, gravestones and brickwork. Many lichen species have disappeared in cities and surrounding areas. This is because the lichens are sensitive to sulfur dioxide - over 65% of SO 2 is produced by fossil fuel burning power stations.

Choosing Which Type of Graph to Draw For each of these tables of data, select the most appropriate form of graph to use...

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