sampling Flashcards
what is random sampling
each member of the target pop has a mathmatically equal chance of being in the experiments sample
how to conduct a random sample
1) list of target pop
2) names into database
3) computer randomly generates
strength of random sample
- avoids researcher bias as they cant choose whose in the sample
- confounding and extraneous variables are equally divided bet diff groups enhancing internal validity
weakness of random sample
- picking by chance means sample could be unrepresentative
- difficult and time consuming to get a full list of target population
what is systematic samping
ppt chosen from list of target pop, eg every 5 th person
strengths of systematic sampling
- avoids researcher bias as they cant choose whose in the sample
- if target pop list already exists (eg register) then it can be a quick method of selecting a sample
limitations of systematic sample
- could result in unrepresentative sample
- hard/time consuming to get a full list of names if target pop is big
opportunity sampling
researcher asks members of pop to take part in research
strength of opportunity sample
- fastest way to get a sample for psychological research reducing time and cost
weaknesses of opportunity sample
- researcher bias, they decide who to ask so could avoid ppl they dont like the look of
- unrepresentative sample which cannot be generalised to wider pop eg asking ppl on one specific street
volunteer sample
ppt offer to take part through advert or online
strengths of volunteer sampling
easy and less time consuming as ppt come to you and easy to distrubute an ad which can reach a large number of people
weaknesses of opportunity sample
volunteer bias - may not be generalisable to wider pop as it attracts a certain type of ppl eg more curious and wants to please reseacher
what is a stratisfied sample
characteristcs of ppt within the sample are on the same proportion as the target population
how to conduct stratisfied sample
stratas are identified along with their proportion in the target pop
use random sampling to generate the correct number of ppt
strength of systematic sampling
- representative of the target pop so can generalise
- randomly chose ppt so no researcher bias
weakness of stratisfied
- not every possible characteristic can be included in stratisfied sample and as researcher decides which strata is important may be some bias
- time consuming to establish strata and then randomly select ppl
