Probability Sampling

INFO

every individual from the population has a chance of being selected as part of the sample

• gives a result that is more indicative of the whole group
• Types of probability sampling

Simple Random Method

• every individual from the group has an equal chance of being selected in the sample
• Example:
  • Rolling a Dice
  • chance of rolling a 4 is $\frac{1}{6}$

Systematic Method

• individuals are assigned numbers, and are selected based on the numbers at regular intervals
• Example:
  • Employees of a company are lined up in the order of the alphabet
  • every 10th person is selected starting from 6th employee
  • sample: 6th, 16th, 26th, etc.

Stratified Method

• individuals are divided into strata or subgroups based on certain criteria (gender, age, income, profession, etc.)
• Ensures that there is a representation from each of the subgroups in the sample
• Example:
  • 100 female and 50 male employees
  • wants to find gender ratio
  • divide the employees into 2 subgroups based on gender
  • sample: around 50 female and 25 male

Cluster Method

• involves dividing the group into subgroups
• the whole subgroup is selected at random
• Example
  • several offices around the country with a similar number of employees in each office
  • Instead of going to each office, only 3-4 offices are selected randomly to get the desired result