Unit 2 Flashcards
What is a population?
A group/set of things you are interested in.
What is a sample?
A subset of a population
What is a parameter?
A number that describes the while population.
What is a statistic?
It is taken from a single sample and can estimate a parameter.
How do a census and sample compare?
A census considers all members of a population, whereas a sample only considers some of the population.
What are the advantages and disadvantages of a census?
Adv:
- guarantees an accurate view of the population
Disadv:
- not possible for an infinite population
- unrealistic when it damages the thing being investigated, e.g. battery lifetime
- time consuming and expensive
What are the advantages and disadvantages of a sample?
Adv:
- can be used for larger or infinite populations
- quicker and cheaper than a census
Disadv:
- can give a misleading view on the population
What is simple random sampling?
Every member of the population is equally likely to be chosen. For example, you could assign each member a number, and then use a random number generator to decide the members of the sample.
What is systematic sampling?
When you divide the population by the sample size (let it be n), and then use every nth member in your sample. For example, with a population size of 100 and a sample size of 5, 100/5 = 20, so you would use every 20th member in your sample.
What us stratified sampling?
When you separate a population into subpopulations, e.g. by age group. You then sample within each group in proportion to size. The formula is (sample size/population size) x stratum.
What is opportunity sampling?
Taking samples from members of the population you have access to until you have a sample of a desired size, e.g. standing in town centre and handing out questionnaires.
What is quota sampling?
When you want distinct groups to be represented in your sample, decide how many members you want in each and do opportunity sampling until you have enough samples for each.
What the qualitative data?
Non numerical data, such as hair colour
What is quantitative data and what are the two types?
Numerical data
Discrete: data that can only take specific values, e.g. how many pets you own
Continuous: data that can take any value in a given range, e.g. mass
What is left/negative skew?
It is when there are more extreme values on the left and most values are found on the right, and the tail is more pronounced on the left.
Mean < median < mode
E.g. 1 2 3 4 100
