What processes are needed to draw conclusions from data?Analysing graphical data

A graph helps to analyse data and can be used to draw a conclusion.

When plotting a graph:

• choose axis scales so that the plotted points occupy at least half the space available (this will help make the graph easier to read)
• label both axes, including the units
• think about whether the line should pass through the origin (0,0)
• choose intervals along the scale that make it easy to plot the points and read off values, eg increments of 2, 5 or 10
• a point that is not near the best fit line is anomalous - it needs to be explained before it can be ignored
• after plotting the point, draw a line of best fit - remember this can be curved

Reading the shape of a graph

A lot can be learnt by looking at the shape of a graph. The gradient is the slope of the graph. For example, when looking at a graph of mass produced against time, the gradient of the graph shows the mass produced per second. This is the rate of reaction.

Example

Finding more data from a graph

Finding values within the range originally measured is called interpolation.

To interpolate a graph, read up from the horizontal axes, then across to find the new value.

Finding values beyond the range that was originally measured is called extrapolation.

To extrapolate a graph, first extend the line. Then read up from the horizontal axis and across to find the new value.