The difference of median months for baby's walk is the ESTIMATE (Fathom calls it a Measure) which changes (variability due to sampling). In the stop motion video there are two arrows or sticks. The longer one shows the difference of medians between the control and treatment groups. The shorter stick shows the difference of medians after one of the randomisations. Just imagine if we had 1000 of these differences (converted to numerical figures) and plotted them into a distribution, that will give us the final answer: 'is chance alone playing a role?'. That's how I see it, is it only a 'gamble' or is there a real difference?. Then only we will be able to say if the experimentation is effective or not.