Analysing graphical data

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

  • 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 regular 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 odd (or 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. 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.

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.

Graph for finding more dataData was only measured for 50 seconds but by extrapolating the line a value can be read for 60 seconds