Data Collection and Sampling Flashcards
To learn all sampling methods and other definitions in statistics.
What is a population?
The whole group.
What is a sample?
A selected group from the population.
What is a sampling frame?
A list of items available to be sampled.
What is a sampling fraction?
The proportion of items available that are actually sampled.
Census - Collect information on every member of population - Method?
Send a survey out to all members of a population.
Simple Random - Every item has an equal chance of being in the sample, each selection independent from others - Method?
- Give number to every member of population (from 1 to n).
- Generate list of random numbers and match them to members to select sample.
- Ignore any repeats.
Systematic - Every nth item in population is selected - Method?
- Give number to every member of population.
- Calculate regular interval to use (pop. size / sample size).
- Generate a random starting point to chose first member, and keep adding the interval to select sample.
Stratified - If population in categories, sample uses same proportions of each category in sample as in population - Method?
- Divide population into categories.
- Calculate number needed for each one (category size / pop. size) x total sample size.
- Randomly select the sample for each category.
Quota - Given a quota of people in each category to interview - Method?
- Divide population into categories.
- Give each category a quota.
- Collect data until all quotas are met (without random sampling).
Opportunity / Convenience - Sample chosen from population is most convenient for sampler - Method?
Choose members of population that are the easiest to sample.
Cluster - When population can be divided into distinct groups, can randomly select groups to survey - Method?
- Divide population into clusters.
- Randomly select clusters to use in sample.
- Use all members of selected clusters (one-stage cluster sample) or randomly sample within clusters to form sample (two stage cluster sample).
Self-Selection / Volunteer - People choose to be part of the sample - Method?
- Advertise or appeal to whole population for participation in sample (could offer payment).
- Either use everyone who responds or take a sample of them to best represent the population.
Probabilities Distributions:
Total of all probabilities in a probability distribution is 1 - expressed as P(X=𝑥) = 1. You can use figures in a distribution to find the mean, or expectation, of the random variable - Σ𝑥 x P(X=𝑥).
