Annual rainfall in Samaru
Drag the red vertical line to highlight the crosses to the left. The proportion of values is displayed at the bottom — the cumulative proportion.
Use the diagram to explain that the proportions below the lower quartile, median and upper quartile are 0.25, 0.5 and 0.75 respectively.
Choose Larger values from the pop-up menu and explain that this is one minus the cumulative proportion.
You could also mention that we need to be careful about equality in this for discrete data — strictly we should use P(X ≤ x) and P(X > x).
In most of Africa, the most important climatic variable is rainfall. Rainfall is usually highly seasonal and failure of crops is normally associated with late arrival of rain or low rainfall. A better understanding of the distribution of rainfall can affect the crops that are grown and when they are planted.
The data set contains the annual rainfall in Samaru, Northern Nigeria, for each year between 1928 and 1983.
We will assume that there was no climate change in this period. From a time series plot of the data, the magnitude of any such trend was much less than the natural year-to-year variation in the rainfalls so it is reasonable to ignore it here.