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 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 .

Example

Question

How does the rate of reaction change over time?

Finding more data from a graph

Finding values within the range originally measured is called .

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

Figure caption,
No data was gathered for the mass produced by 25 seconds, but it can be interpolated from the graph

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

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

Data was only measured for 50 seconds but by extrapolating the line a value can be read for 60 seconds. — Figure caption,
Data was only measured for 50 seconds but by extrapolating the line a value can be read for 60 seconds

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