15. Sampling Flashcards
1
Q
Basic key terms of selecting a sample
A
- The part of a population that you’re interested in studying is called the target group (eg. all the ppl in a particular city, or all ppl of a certain age).
- Usually you cant include everyone in the target group in a study, so you choose a certain sample of participants.
2
Q
What should a sample be
A
- The sample should be representative (it should reflect the variety of characteristics that are found in the target group) so that the results can be generalised to the whole target group.
- A sample that is unrepresentative is biased & cant reliably be generalised to the whole target group.
3
Q
5 main ways of selecting a sample
A
- Random sampling
- Opportunity sampling
- Volunteer sampling
- Systematic sampling
- Stratified sampling
4
Q
What is Random sampling
A
- This is when every member of the target group has an equal chance of being selected for the sample.
- This is done either manually or by a computer. MANUALLY: each person could be assigned a no. Each no. could be put in a hat, & then no.’s selected at random from it. USING A COMPUTER: everyone in the target group could be given a no., then the computer could randomly pick no.’s to select P’s (rand. no. generator).
5
Q
ADVANTAGES of Random sampling
A
- Random sampling is ‘fair’. Everyone has an equal chance of being selected & this sample is likely to be representative.
6
Q
DISADVANTAGES of Random sampling
A
- This method doesnt guarantee a representative sample - theres still a chance that some subgroups in the target group may not be selected (eg. ppl from a minority cultural group).
- ALSO, if the target group is large, it may not be practical (or possible) to give everyone a no. that might be picked. So in reality, completely random samples are rarely used.
7
Q
What is Opportunity sampling
A
- This is when the researcher samples whoever is available & willing to be studied.
- Since many researchers work in universities, they often use opportunity samples made up of students.
8
Q
ADVANTAGES of Opportunity sampling
A
- This is a quick & practical way of getting a sample.
9
Q
DISADVANTAGES of Opportunity sampling
A
- The sample is unlikely to be representative of the target group or population as a whole. This means that we cant confidently generalise the findings of the research.
10
Q
What is Volunteer sampling
A
- When ppl actively volunteer to be in a study by responding to a request for P’s advertised by the researcher.
- The researcher may then select only those who are suitable for the study.
(eg. used by MIlgram)
11
Q
ADVANTAGES of Volunteer sampling
A
- If an advert is placed prominently (eg. in a national newspaper) a large no. of ppl may respond, giving more P’s to study. This may allow more in-depth analysis & more accurate statistical results.
12
Q
DISADVANTAGES of Volunteer sampling
A
- Even though a large no. of ppl may respond, these will only include ppl who saw/heard abt the advertisement - no one else would have a chance of being selected.
- ALSO, ppl who volunteer may be more cooperative than others, so the sample is unlikely to be representative of the target population.
13
Q
What is Systematic sampling
A
- This is where every nth name from a sampling frame (a record of all the names in a population) is taken (eg. every 3rd name from register, or every 50th name from a phone book).
- This is useful IF there is a sample frame available.
14
Q
ADVANTAGES of Systematic sampling
A
- This is a simple & effective way of generating a sample w a random w a random element.
- It also means the population is more likely to be evenly sampled than by using opportunity or volunteer samples.
15
Q
DISADVANTAGES of Systematic sampling
A
- Subgroups might be missed. It will not be representative if the pattern used for the samples coincides w a pattern in the population.
16
Q
What is Stratified sampling
A
- Where all of the important subgroups in the population (eg. different age or ethnic groups) are identified & a proportionate no. of each is randomly obtained.
- Eg. in a class of 20 students, ten are 16yrs old, eight are 17yrs old, & two are 18yrs old.
If you take a Stratified sample of 10 students, the no. of 16, 17, 18yr olds in the sample will need to be 50% of the full class. So you’ll need five 16, four 17, & one 18yr old in your stratified sample.
17
Q
ADVANTAGES of Stratified sampling
A
- This can produce a fairly representative sample. It can also be used w random & systematic sampling.
18
Q
DISADVANTAGES of Stratified sampling
A
- It can take a lot of time & money to do, & some subgroups may be missed.
- It can often be difficult to identify traits & characteristics (such as ppl’s ages or backgrounds) effectively enough to stratify the sample properly.
