3.2c Sampling and reliability Flashcards
When is a representative sample of the population selected?
where it is impractical to measure every individual
What determines the appropriate sample size?
the extent of the natural variation within a population
When is a larger sample size required?
more variable populations
What should a representative sample have?
- it should share the same mean and the same degree of variation about the mean as the population as a whole
What are the 3 types of sampling?
- random
- systematic
- stratified
What is random sampling?
members of the population have an equal chance of being selected
What is systematic sampling?
members of a population are selected at regular intervals
What is stratified sampling?
the population is divided into categories that are then sampled proportionately
What may variation in experimental results be caused by?
- reliability of measurement methods
- and / or inherent variation in the specimens
How can the reliability of measuring instruments or procedures be determined?
by repeated measurements or readings of an individual datum point
the variation observed indicated the precision if the measurement instrument or procedure but not necessarily its accuracy
How can the natural variation in the biological material be determined?
by measuring a sample of individuals from the population
What does the mean of these repeated measurements give?
the mean of these repeated measurements will give an indication of the true value being measured
What is a measure of the extent of variation in the results?
the range of values
What is the variation if there is a narrow range of results?
low
Why should independent replication be carried out?
to produce independent data sets
