Sampling

It is usually impossible to count or measure every individual in a population, so biologists take a sample. The sample is used to estimate the characteristics of the whole population.A sample must be representative of the population. If it is not, any conclusions drawn from it may not be valid.Sampling bias happens when the investigator, consciously or not, chooses individuals that are not typical, for example the largest plants or the most accessible areas. Bias is reduced by using random sampling.Chance also affects a sample. The individuals chosen may, by chance, not be typical of the population. The effect of chance is reduced by using a large sample size.The larger the sample, the more likely it is to be representative and the more reliable the estimate. Taking a large number of samples and calculating a mean also reduces the effect of any unusual results.When investigating biodiversity or genetic diversity within a species, samples should be taken in the same way in each area being compared, so that differences are due to the organisms and not to the method.