2.2.5 Sampling Flashcards
(27 cards)
Opportunity sampling
When ptps are recruited based on who is most convinient or most available
e.g people walking by you in the street
e.g students at your school
Give 1 advantage of Opportunity sampling
- the easiest methods - you jsut use the first sutiable ptps you can find
> less time consuming to locate sample
Give 1 disadvantage of Opportunity sampling
- biased > sample is drawn from a small part of target population
e.g selecting sample from people walking around town would likely exclude ptps such as profesionals at work or people in rural areas
Random Sampling
each item in a target population has an equal chance of being selected
- methods can be used such as lottery method and random number generators
what is the Lottery Method of Random sampling
An easy method of random sampling where:
- list of people in target population is obtained
- all the names are put into a hat or barrel
- you select the number of names required
if a researcher is using this method for random allocation of ptps to groups, they might put first 10 names drawn in group A and second 10 names in group B
what is a random number generator and how does it work
a device such as a calcualtor that has the fucntion to gernerate a random number
- every member of the target population gets numbered
- using, for example, mciorsoft excel you can type in a code to get a random number between 1-100
e.g =RAND(100)
give 1 advantage of random sampling
- unbiased (all ptps have equal cahnce of selection)
give 1 disadvantage of random sampling
- time consuming
> need to create list of ptps in target population and contact all
Snowball Sampling
current ptps recruit further ptps from among people they know
> sample group appears to grow like a snowball
give 1 advantage of snowball sampling
- enables a researcher to locate groups of people who are difficult to access
e.g drug addicts
give 1 disadvantage of snowball sampling
- the sample is not likely to be a good cross-section from the population becuase it is friends and family
Self-Selected Sampling
advertisement in a newspaper or on a noticeboard or on the internet
give 1 advantage of self-selected sampling
- gives access to a variety of ptps (e.eg everyone that reads the newspaper)
> may make the same more representative and less biased
give 1 disadvantage of self-selected sampling
- the sample is biased in other ways because ptps are liekly to be more highly motivated to be helpful, and/or with extra time on their hands
> results in volunteer bias
Stratified Sampling
subgroups (strata) within a target population are identified (e.g boys and girls, or age groups: 10-12 years, 13-15 years)
- ptps are obtained from each strata in proportion to their occurence in the target population
for stratified, selected from the strata is done using a random technique
for quote, selcetion is done using a non-random technique
give 1 advantage of stratified/quota sampling
- likely to be more representative than other methods
> there is a proportional representation of subgroups
give 1 disadvantage of stratified/quota sampling
- very time consuming to identify subgroups and then select ptps and contact them
Systematic Sampling
Using a predetermined system to select ptps such as selecting every 6th, 14th, 20th (or whatever?!) person from a phonebook
- the numerical interval is applied consistently
give 1 advantage of systematic sampling
- unbiased as ptps are selected using an objective system
give 1 disadvantage of systematic sampling
- not truly unbiased/random unless you select a number using a random method and start with this person, and then select every Nth person
Sampling Frame
The source material from which a sample is drawn
Target Population
- the group of people the research is interested in
- the group of people from whom a sample is drawn
- the group of people about whome generalisations can be made
Bias
a systematic distortion
Generalisation
applying the findings of a particular study to the target population
