A powerful way of looking at your data and getting to know it, as well as engaging other people in discussing it, is visualisation. In the case of SPSS, this means creating graphs.
We have just (on the Aggregates page) created a time line for the number of people enslaved per year by ships based in Liverpool. We can, of course, scan the column of numbers to try to find out what is going on, but we can easily miss trends by doing that. It is much easier to look at a graph.
To create a graph, go to Graphs and select Chart Builder.
A dialog box will open giving you friendly warnings about making publication quality charts. For the moment, click on OK.
The Chart Builder dialog opens. This works by dragging a dropping elements in the main part of the box. First, select the sort of graph you want (bar, line, etc) and drag the specific graph type to the window – in this case we have a simple line chart. Then drag the axes from the leftmost box the the x-axis (yearam) and the y-axis (number_sum).
When you are ready, click on OK. The graph will be drawn in the output window.
The graph can be copied or exported for the pop-up menu obtained by right clicking on it in the output window.
Already we can see some features which would be harder to observe from the list of years and numbers. We can see that the slave trade peaked in around 1800, for example, and we can also check the precise date by referring to the dataset (specifically the peak was in 1799). We can also see a large feature which should intrigue us as researchers around 1780. While we might have spotted this in the numbers it is far easier to see that it is a major feature in the trajectory of the Liverpool slave trade, and would need further investigation – the probability is that as the dates coincide with the American Revolutionary Wars, the dip in the slave trade is as a result of the war.
We can also see that the Liverpool slave trade ended in 1807, the year when the slave trade was banned within the British Empire, although slaves were not freed until 1834 in the Empire, and even then it took some years for slaves to be even technically free – they became unpaid ‘apprentices’, a system that was only abolished in 1838.
Durham SPSS 