Nayland College  Mathematics Home . Year 9 . Year 10 . Level 1 . Level 2 . L3 Statistics . L3 Maths . L3 Calculus . About . Links 
10 
Is the observed difference by random chance? (Excellence) Video Chris Wilds overview of sample variation etc, (view from 20:10 for randomisation) Treat the data as completly randomly allocated. Resample from the randomly grouped sample data and find the probability that the observed group difference would happen by random chance. If the chance of the observed difference occurring is low then this indicates that the two group population medians (or means) would be different. If the chance of the observed difference occurring is NOT low then this indicates that the two group population medians (or means) cannot be seen to be different. 
Class notes,
Class notes
Class site

We want to compare a control group to a test group Does the experiment cause the difference seen between the groups (or could it be by random?)
Does exercising a baby lower the age of first walking? The Randomisation test is a way to find out if the observed difference is by chance or not. Resamples are taken from the sample and the groups are randomly allocated to the resample data The difference between the two (randomly allocated) groups is found. This is repeated (1000 times) and a distribution of the differences is formed. The distribution is used to calculate the probability that the actual observed difference would happen. 

If this is a low probability then this would indicate that the ‘test’ group population median (or mean) is statistically different from the control group. If this is not a low probability then this would indicate that the ‘test’ group population median would not statistically different from the control group median (or mean). Using the Mean instead of Median 
