Statistics C1 Flashcards
Definitions
Population
The whole set of items that are of interest
Census
Observes or measures every member of a population
Sample
A selection of observations taken from a subset of the population which is used to find out information about the population as a whole
Adv of a Census
It should give a completely accurate result
Dis of Census
Time consuming
Expensive
Cannot be used if it destroys the item
Adv of a sample
Less time consuming
Less expensive
Less data to process
Did of a sample
May not be accurate
May not be large enough to give information about all sub groups of a population
Sampling units
Individual units of a population
Name 3 methods of random sampling
Simple random sampling
Systematic sampling
Stratified sampling
Systematic sampling
The required elements are chosen at regular intervals from an ordered list.
EG- sample size of 20 from population of 100
100÷20=5 interval
Stratified sampling
The population is divided into mutually exclusive strata (males and females) and a random sample is taken from each
Number samples in a stratum = (number in stratum/number in population)×overall sample siza
Adv of Simple random sampling
Free of bias
Easy and cheap for SMALL populations and samples
Did of Simple random sampling
Not good for BIG populations or samples
A sampling frame is needed
Adv of Systematic sampling
Simple and quick
Good for large samples and populations
Dis of Systematic samplinf
A sampling frame is needed
It can introduce bias if sampling frame isn’t random
Adv of stratified sampling
Accurately represents population
Guarantees proportional representation
Dis of stratified sampling
Population must be classified in strata
A sampling frame is needed
Quota sampling
An interviewer selects a sample that reflects the characteristics of the whole population
Opportunity/convenience sampling
A sample is taken from people available at the time who fit the criteria
Adv of quota sampling
No sampling frame needed
Inexpensive and quick
Easy comparison between groups
Allows small sample to be representative
Dis of quota sampling
Non-random could be biased
Population must be in groups
Increasing scope makes it expensive
Dependent on an individual researcher
Quantitative variables
Numerical data
Qualitative variables
Non numerical values
Continuous variable
Can take any value
Discrete variable
Can only take specific values
EG: Number of girls in value cannot be 2.85 it has to be 2 or 3
Sampling frame
A list of the names or number of every unit in a population
