Variation - BIOL2 AS

INTERSPECIFIC VARIATION - when one species differs from another. 

INTRASPECIFIC VARIATION - when members of the same species differ from one another. 

SAMPLING - not all measurements can be classed as representative: 

Sampling Bias - The selection process may be biased, investigators may be making unrepresentative choices, deliberately or unwittingly. 

Chance - Even if sampling bias is avoided, the individuals chosen, may be by pure chance, unrepresentative. 

To reduce sample bias, random sampling is carried out: 

1. Divide the study area into a grid of numbered lines, e.g by stretching two long tape measures at right angles to each other. 

2. Using random numbers, from a table or generated by a computer, obtain a series of coordinates. 

3. Take samples at the intersection of each pair of coordinates. 

To minimise the effects of chance: 

Large Sample Size…