Maths
Define a 'population'
A group that we want to find information about
Define a 'Census'
Where information about every member in the population is collected
Define a 'Sample Survey'
where information is collected from a small representation of a population
Define a 'Sampling Unit'
A person/object from a population being sampled
Define a 'Sampling Frame'
The collection of all sampling units from a population
Give advantages and disadvantages of Random Sampling
Advantages - Can be completely unbiased as everyone has an equal chance of being selected
Disadvantages - The sample may not represent the population due to random fluctuations
Give advantages and disadvantages of Systematic Sampling
Advantages - Simple and quick to use
- Suitable for large samples & populations
Disadvantaged - Needs a Sampling Frame
- Can be biased if the sampling frame isn't needed
Give Advantages and Disadvantages of Stratified sampling
Advantages - Accurately reflects population structure
- Guarantees proportional representation of group within a population
Disadvantages - population must be clearly classified into distinct strata
Name 2 types of non-random sampling
- Opportunity Sampling
- Quota Sampling
Give advantages and disadvantages of quota sampling
Advantages - No sampling frame needed
- Quick, easy and inexpensive
- Allows a small sample to still be representative of the population
- Allows easy comparison between groups in a population
Disadvantages - non-random can introduce bias
- population must be divided into groups which can be costly
- Increasing scope of study increases the noof groups, which adds time and expense
Give advantages and disadvantages of opportunity sampling
Advantages - Easy to carry out
- Inexpensive
Disadvantages - unlikely to give a representative sample
- Dependent on researcher
Define a 'Simple Random Sample'
a sample (size n) where every sample of size n has an equal chance of winning
Define a 'Systematic Sample'
A sample where elements are chosen in regular intervals of an ordered list
Define a 'Stratified Sample'
A sample where the population is divided into mutually exclusive strata & a random sample is staken from each
Define a 'Quota Sample'
Where an interviewer selects a sample that reflects the entire population
Define a 'Opportunity Sample'
Taking a sample from people who are available at the time the study is carried out
How can the probability of a random variable be described
- A probability mass function
- A table
- A diagram
What is the distribution called if all probabilities are the same
discrete uniform distribution
When can you model X with a binomial distribution
- If there are a fixed no of trials
- If there are 2 possible outcomes
- There's a fixed probability of success
- The trials are independent of each other