This variation makes it difficult for us to be certain about our results. It also causes problems when we wish to compare beech leaf size in different habitats. Beech trees vary in age and condition. Sampling may vary. In the case of beech leaves it may rain one day and be sunny the next.
Chance plays a part, especially with small sample sizes.
A twig may just happen to have only large leaves. To get this you add up all your results and divide by the number in the sample. Work out the average length and mass of the beech leaves from the sun and shade branches in the space below. Tabulate your results and leave plenty of space on the right hand side of your table so that you can add more columns later. In order to get an idea of how much they vary we calculate what is called the standard variation.