Sampling, Observations, Self Report & Correlations

What are the sampling techniques?

• opportunity

• Random

• Systematic

• Stratified

• Volunteer

Define opportunity sampling

recruit those people who are the most convenient, or who are available at the time

Define random sampling

• all members of the target population have an equal chance of being selected

• Uses a lottery method - out of hat or random number generator

Define systematic sampling

use a predetermined system to select participants; every nth member of the target population. The interval (n) consistently throughout the population

Define stratified sampling

• strata (subgroups) within the population are identified

• Ps are randomly selected from each of the strata in proportion to the strata's occurrence in the population

• Sort your population into subgroups - these are your strata

• Work out proportions of each strata in the population

• Work out the number that needs to be randomly selected from each strata

• Use a lottery number method to randomly select

Define volunteer sampling

An advert is placed somewhere for participants to respond to it (self-select)

What are strengths of opportunity sampling?

quick, easy, convenient - takes less time to locate your sample

What are the strengths of random sampling?

everyone in the population has an equal chance of being selected (unbiased)

What are the strengths of systematic sampling?

Likely to be more representative - consistent (unbiased)

What are the strengths of stratified sampling?

Likely to be more representative - more proportional and randomly selected representation of subgroup

What are the strengths of volunteer sampling?

• Gives access to a variety to participants

• May make sample more representative and less biased

What are the limitations of volunteer sampling?

• Sample is biased in other ways - higher chance of highly motivated participants with extra leisure time

• Volunteer bias - might be more highly motivated to be helpful

What is the imitation of stratified sampling?

Very time consuming to identify subgroups then randomly select participants

What are the limitations of systematic sampling?

• Need to have list of all members of population

• Almost excluding the first few people in the list - not truly unbiased unless you have a random starting point

What are the limitations of random sampling?

• biased sample by chance

• Time consuming

What are the limitations of opportunity sampling?

• it is inevitably biased - sample drawn from small part of population

  • e.g. going into Abingdon at 10am on a Monday morning, anyone who works full time or is in education won't be there