S2 - Chapters 6-7 Flashcards
Statistic
A random variable (1) which is some function of the sample and not dependent on any population parameters (1)
Population
The collection of all items
Sample
Some subset of the population which is intended to be representative of the population
Census
When the entire population is sampled
Sampling Unit
Individual member or element of the population or sampling frame
Sampling Frame
A list of all sampling units or all the population
Sampling Distribution
All possible samples are chosen from a population (1); the values of a statistic and the associated probabilities is a sampling distribution (1)
Advantages of taking a census
- every single member of the population is used
- it is unbiased
- gives an accurate answer
Disadvantages of taking a census
- takes a long time to do
- costly
- often difficult to ensure that the whole population is surveyed
Sample Survey
an investigation using a sample
Advantages of sampling
- if a population is large and well mixed, a sample will be representative of the whole population
- sampling is generally cheaper than taking a census
- advantageous where the testing of items results in their destruction
- when using a sample rather than a census, data is generally more readily available
Disadvantages of sampling
- there is an uncertainty about sampling in that there will be natural variation between any two samples due to the natural variation between the individual units that make up the samples
- bias - anything that occurs when taking a sample which prevents it from being truly representative of the population from which it is taken
- bias can occur if you sample from an incomplete sampling frame
- bias can also occur if the person taking the sample allows their personal feelings to influence the choice
Population Parameter
any characteristic of population that is measurable
