Participants

• Target Population

  The group of individuals a researcher is interested in

  Sampling Frame

  The smaller group from the target population the researcher is going to sample their ppt from

  Sample Group

  The ppt actually used in the research taken from the sample frame
• Opportunity: Choosing who are available at the time

  +Quicker and easier than stratified, choosing whose available at that time

  +Appropriate when sampling frame is unknown

  -Results in biased sample, small sample taken from a place where all ppts are (same characteristics potentially)

  -Increased researcher bias, approach those who appear to fit reserach, lowers internal validity
• Self-selected: Advertise in newspaper for ppts, they volunteer to take part

  +More ethical, sure they have given consent as they volunteered

  +Quick and easy method since researcher only has to place advertisement, ppts come to them

  -Volunteer bias risk, certain people more likely to participate than others

  -Demand characteristics as some may be eager to help researcher
• Systematic: Use predetermined system (every 14th for example) to select every nth ppt from target population

  +Lowers research bias as ppt selected using objective system

  +Quicker, do not need to establish proportions of different groups within population

  -Results in biased sample, system may result in 'freak' unrepresentative sample

  -Not practical when sample frame is unknown
• Random: List of all in target population, write names on paper and place in hat, select the amount needed

  +Unbiased, all have equal opportunity being selected, generalisable

  +Lowers researcher bias, random selector chooses rather than researcher

  -Time consuming to identify everyone then select randomly

  -Biased sample as chance of 'freak' unrepresentative result
• Snowball: Find one ppt, they recruit further amongst people they know that relate to what you need

  +Useful wehn ppts are difficult to research e.g. addicts

  +Appropriate when sampling frame is unknown

  -Unrepresentative, friends and family may be used, harder to generalise

  -Time consuming, researcher waits for ppts to be referred
• Stratified: Subgroups within target population identified, ppts gained from each in proportion to rate they appear then random technique to select

  +Most representative, proportional representation of subgroups, generalisable

  +Lowers researcher bias as random technique chooses ppt

  -Time consuming as all subgroups need to be identified then selected randomly

  -Some bias as not all subgroups can be identified
• Quota: Subgroups within target population identified, ppts gained from pre-set numbers from each group, then non-random techique

  +Most representative, proportional representation of subgroups, generalisable

  +Quicker than stratified

  -Time consuming as all subgroups need to be identified then selected through opportunity

  -Researcher bias as non-random may choose someone who appears to suit research