statistics Flashcards
What is discrete uniform probability?
When all the probabilities are the same.
What is a random variable?
a variable whose value depends on the outcome of a random event.
What is a discrete variable?
A variable that can only take certain numerical values.
What is a sample space?
the range of values that a random variable can take
When can you model x with a binomial distribution?
when there’s a fixed no.of trials
there’s two possible outcomes
there’s a fixed probability of success
the trials are independent of each other.
What is a population
the whole set of items that you’re interested in
What is a census?
something that observes or measures every member of a population
What is a sample?
it’s a selection of observations taken from a subset of the population which is used to find out info about the population as a whole
What is a simple random sample?
A type of sample where the items in the sample are chosen by a random procedure.
what is a systematic sample?
A sample where the required elements are chosen at regular intervals from an order list
What is a stratified sample?
A type of sample where the population is divided into mutually exclusive strata and a random sample is taken from each
What is quota sampling?
A type of sampling where an interviewer or researcher selects a sample that reflects the characteristics of the whole population
What is an opportunity sample?
A sample where you ask people that are available at the time of the study and fit the criteria you’re looking for
What are the advantages of using a census?
it should give a completely accurate result.
What are the disadvantages of using a census?
- Time consuming + expensive
- cannot be used when the testing process destroys the item.
- Hard to process large quantity of data
What are the advantages of using a sample?
- Less time consuming and expensive than a census.
- Fewer people have to respond
- less data to process than a census
What are the advantages of using a simple random sample.
Free of bias
easy and cheap to use for small populations and small samples.
each sampling unit has a known and equal chance of being choosen
What are the disadvantages of using a simple random sample?
- Not suitable when the population size or the sample size is large as it is potentially time consuming disruption and expensive.
- A sampling frame is needed
what are the advantages of stratified sampling?
Sampling accurately reflects the population structure.
guarantees proportional representation of groups within a population
What are the disadvantages of using stratified sampling?
- Population must be clearly classified into distinct strata.
- selection within each stratum suffers from the same disadvantages as Simple random sampling
What are the advantages of using systematic sampling?
Simple and quick
suitable for large samples and large populations.
What are disadvantages of using systematic sampling?
A sampling frame is needed
it can introduce bias if the sampling frame is not random
What are the advantages of using quota sampling?
Allows a small sample to still be representative of the population.
No sampling frame needed
quick , easy and cheap
allows for an easy comparison between groups within a population.
What are the advantages of using an opportunity sample?
Easy to do
Cheap
