(5) Sampling

• in psychological research, people are needed to study human behaviour
• participants = groups of people
• the participants that form part of a research studies are selected through the process of sampling
• the five different sampling techniques are :

  • random sampling
  • systematic sampling
  • stratified sampling
  • opportunity sampling
  • volunteer sampling
• sampling techniques are used to accurately represent a 'population'
• population = a large group individuals that are particular researcher is interested in studying
• Target Population = the people or groups that are the focus of the research - subset of the general population
• sample = participants in a study who are selected to take part in a study.
• researchers uses a sample for practical and economic reasons as it usually not possible to include all members of a target population
• target population = group of people that are being studied
• ideally the sample that is drawn will be representative of the target population so that generalisation of findings become possible
• in reality, it is quite difficult to represent a population in any given sample due to the inevitably diverse nature of populations of people
• most samples have a degree of bias thus sample techniques aim to produce a representative sample
• Random Sample :

  • sophisticated form of sampling
  • all members of the target population have an equal chance of being selected
• Process of Random Selection

  • first : a complete list of all members of the target population is obtained
  • secondly : all members of the list are assigned a number - helps reduce bias + confidentiality
  • thirdly : sample is generated through the use of some lottery method [eg random number generator or number from a hat (until you have a full sample)]

  used in random sampling
• EVALUATION of Random Sampling

  Strength :

  • free from researcher bias
  • researcher has no influence over who is selected - prevents them from choosing people who they think may support their hypothesis
• EVALUATION of Random Sampling

  Weaknesses :

  • difficult and time consuming to conduct - complete list of target population may be difficult to obtain
  • may end up with a sample that is unrepresentative - still possibility to select people with similar characteristics
  • selected participants may refuse to take part - so possibly end up with something similar to a volunteer sample - unrepresentative
• Systematic Sample :

  • every nth number of a target population is selected
  • sampling frame is produced - a list of every person in the target population organised into a specific order (usually alphabetical)
  • sometimes researcher starts from a random selected point on the list to reduce bias
  • researcher works through the sample frame until the sample is complete (when they get to the end of the list)
• EVALUATION of Systematic Sample

  Strength :

  • avoids researcher bias
  • researcher has not influence over who is chosen once the system for selection has been established
  • fairly representative
• EVALUATION of Systematic Sampling

  Weaknesses :

  • People can still refuse to take part - result in an unrepresentative sample
  • possible to get a sample with the same characteristics (eg all male), despite using a systematic method
• Stratified Sampling :

  • the composition of the sample reflects the proportions of people in certain sub groups (strata) within the target population
  • Researcher first identifies the different stratas that make up the population
  • secondly : proportions needed for the sample to be representative are worked out
  • thridly : participants from different stratas are selected using random sampling
• EVALUATION of Stratified Sampling

  Strengths :

  • avoids researcher bias : participants are randomly selected - beyond the influence of the researcher
  • produces a representative sample : accurately reflects the composition of the population (directly proportional) - generalisation of findings become possible
• EVALUATION of Stratified Sampling

  Weaknesses :

  • the identified strata cannot reflect all the ways that people are different
  • complete representation of the target population is not possible
  • participants could refuse to take part
  • time consuming : long process to find the different stratas/ participants
• Opportunity Sampling :

  • researchers select who are willing and available
  • the researcher asks who is around at the time of their study (eg in the street)
• EVALUATION of Opportunity Sampling

  Weaknesses :

  • sample suffers from bias
  • sample is unrepresentative of the target population as it is drawn from a specific area - findings cannot be generalised to target population
  • biased : common sample that is used is students who happen to be studying psychology - are available to researchers
  • researcher bias : researcher has complete control over the selection of participants - may avoid people they do not like the look of (eg drunk people of the streets)
• Volunteer Sampling :

  • participants select themselves to be part of the sample - self selection
  • Researcher may place an advert in a newspaper/ online/ TV adverts
  • willing participants may raise their hand when the researcher asks
• EVALUATION of Volunteer Sampling

  Strength :

  • easy to collect a volunteer sample - requires minimum input from the researcher
  • less time consuming
• EVALUATION of Volunteer Sampling

  Weaknesses :

  • volunteer bias is a problem : may attract a certain 'profile' of person - someone who is helpful, keen and curious
  • demand characteristics - participants with these characteristics will try to please the experimenter - unnatural behaviour affects the DV
  • presence of demand characteristics may affect how far findings can be generalised