3
There are ā¦ types of random sampling
simple random, systematic, stratified
examples of random sampling
when every member of the population has an equal change of being selected
random sampling isā¦
2
There are ā¦ types of non-random sampling
quota, opportunity
examples of non-random sampling
when a subjective method is used to select members from a population
non-random sampling isā¦
sampling where every member has an equal chance of being selected
simple random sampling definition
number each member of the population
use a calculator/random generator to pick X numbers at random
select the members that correspond to the numbers drawn out
simple random sampling steps (3)
free of bias
easy and cheap for small samples/populations
advantages of simple random sampling
a sampling frame (a list of everyone in the population) is needed
ā“ not suitable for larger samples/populations
disadvantages of simple random sampling
sampling where the required members are chosen at regular intervals from an ordered list
systematic sampling definition
number the list in an order (of some sort)
pick a member of the list at random to start at
divide the size of the population by the sample size to find the interval between each member
pick each member that are Y interval apart until sample size is full
systematic sampling steps (4)
simple and quick to use
suitable for large samples/populations
advantages of systematic sampling
a sampling frame (a list of every member in the population) is needed
bias is introduced if the sampling frame is not randomly ordered
disadvantages of systematic sampling
sampling where the population is split into disjointed, representative groups (such as by ethnicity, by age, by gender) in order to allow sampling to be more proportionate
stratified sampling definition
find the overall population size
split the population into smaller groups
divide each group by the total, to find out what proportion of the population the group takes up
times that percentage by the sample size to find out how many data values to take from each group
use a random number generator to produce the required quantity of random numbers in each category
stratified sampling steps (5)
the sample accurately reflects the population structure
there is a proportional representation of any group in the population
advantages of stratified sampling
the groups must be distinct - if they are not, the method becomes inefficient
a sampling frame is still needed
this is not suitable for large samples/populations
disadvantages of stratified sampling
a researcher selects a sample based on who is available at the time of study (e.g. the first 50 people that walk past, the last 20 people in the shop)
opportunity sampling definition
the researcher identifies criteria for their participants
they then ask anyone who falls into that criteria whether they would be a part of the investigation
opportunity sampling steps
easy and inexpensive
advantages of opportunity sampling
unlikely to provide a representative result
highly dependent on individual researcher and situation
disadvantages of opportunity sampling
sampling when the population is split into groups (like stratified sampling) and members of the population are selected until each quota is filled
quota sampling definition
The population is divided into groups according to a given characteristic (e.g. age). The size of each group determines the proportion of the sample that should have that characteristics
An interviewer meets people, assess their group and then (after interview) allocate them into the appropriate quota (e.g. 10 participants age 18-22 don't like ice-cream)
This continues until all the quotas have been filled - if a person refuses to be interviewed, or the quota which they fit into is full, they are ignored, and the interviewer moves onto the next person
quota sampling steps
allows a small sample to be representative of the population
no sampling frame is needed
quick, easy and inexpensive
advantages of quota sampling
population must be divided into groups, which can be costly and inaccurate
non-responses are not recorded, making the data more bias
disadvantages of quota sampling
collects data aboutĀ allĀ the members of aĀ population
census
used to collect data from aĀ subset of the population
sampling