[LBOLYTC] Unit 3: Sampling Methods

Random Sampling

select n elements from a population in such a way that every set of n elements in the population has the same chance of being selected

Random Sampling

In order to select a random sample of n elements from a population, we make n random selections- 1 at a time – from the population.

2 Types of Random Sampling

Sampling w/ Replacement
Sampling w/o Replacement

Sampling w/ Replacement

• Placing the element (ex. individual) chosen on any particular selection back into the population

• The element has a chance to be chosen on any succeeding random selection

Sampling w/o Replacement

• Not placing the element chosen on a particular selection back into the population

• The element no longer has a chance to be chosen on

  any succeeding random selection

Probability Sampling

A sampling where we know the chance (or probability) that each element in the population will be included in the sample

Probability Sampling

sample obtained can be used to make valid statistical inferences about the sample population

4 Types of Probability Sampling

Simple
Systematic
Stratified
Cluster

Simple Random Sampling

all subjects of a population have a chance to be chosen

Systematic Random Sampling

picking the nth person

Stratified Random Sampling

dividing the population into smaller groups; randomly selecting from these groups proportionally

Cluster Random Sampling

used when natural groups occur in a population; population is subdivided into groups and random samples are then gathered from each group

3 Types of Non-Probabilistic Sampling

Convenience
Voluntary Response
Purposive

Convenience Sampling

we select elements because they are easy or convenient to use

Voluntary Response Samples

A type of convenience sampling where participants self-select – that is, whoever wishes to participate does so 

Purposive Sampling

a person who is extremely knowledgeable about the population under consideration selects population elements that he or she feels are most representative of the population

Slovin’s Formula

n = N / (1 + Ne²)