Interspecific variation = when one species differs from another.
Intraspecific variation = when members of a species differ from members of the same species.
- usually measuring aspect of living organisms and all living organisms are different.
- need lots of measurements.
- can't accurately measure using just one, and can't measure all in existence.
- to get around this, biologists use samples.
Sampling = taking measurements of individuals from the population of organsims being investigated.
Theoretically, individuals are representative of population. However, sample could be unreliable:
- Sampling bias: unrepresentative choices by investigators, intentionally or unintentionally e.g. likely to pick buttercups from area covered in nettles or cow dung?
- Chance: by pure chance may not be representative.