sampling

• what is opportunity sampling?

  recruiting those who are readily accessible and available 

  For example someone walking down street 
• what is sampling?

  the method used to select participants
• strength and limitation of opportunity sampling

  Strength - less time consuming, easy to collect lots of data which is easier to see the consistency of results

  Limitation - biassed , sample only drawn from small part of population, not representative
• what is Random sampling?

  Selecting participants where everyone in the population has an equal chance of being picked
• random techniques

  1. Lottery technique - draw names out of hat

  2. Random number table - every person has a number, blindly place finger and read number from that point

  3. Random number generators 
• what is Stratified sampling -  researchers divide subjects into subgroups called strata based on characteristics that they share (e.g., race, gender, educational attainment). Once divided, each subgroup is randomly sampled 
• strengths and limitations of stratified sampling

  strength - proportional representation of subgroups (representative) whilst still being random

  limitation - very time consuming to identify sub groups and then select and contact
• • what is Systematic? using predetermined system like phonebook to select from an number interval which is applied consistently (eg 1st person 3rd 5th 7th)
• strength and limitation of systematic

  • Strength Unbiased - selected using an objective system
  • Limitation - not truly unbiased unless you select starting number randomly
• what is the difference between a population and a sample

  A population is the entire group that you want to draw conclusions about.

  A sample is the specific group that you will collect data from.

  The size of the sample is always less than the total size of the population.

  eg. Undergraduate students in the UK

  300 undergraduate students from three UK universities who volunteer for your psychology research study
• strengths and limitations of random sampling

  unbiased as everybody has an equal chance of selection

  • make take some time and you have little control of participant variables
  • not completely unbiased as some people who were selected mayh not want to take part
  • not proportional representation of subgroups
• what is a volunteer sample 


  a sample which relies soley on people putting themselves forward for the study

  eg. adverstising in a newspaper
• volunteer strengths and limitations

  strength- acess to lots of partcipants, representative

  less ethical issues as they volunteered so will give full informed consent

  limitation -volunteer bias- those vokunteering will have special characteristics like being especially motivated and confident
•  Using this method, the researcher has to put each name (or an assigned number) on a separate slip of paper and place them all in a container. The researcher then selects 100 slips from the container. The following conditions could apply: the container should be shaken between each draw; the slips of paper should all be the same size and folded in the same way so that one does not feel different from another; the selector draws 'blind' ie cannot see the actual slips of paper.