sampling techniques Flashcards
What is a stratified sample?
Composition of the sample reflects the proportions of people within each of the sub groups of the target population.
How is stratified sampling obtained?
-The researcher identifies the different stata(subgroups) that make up the population.
-Then calculates the size(relative percentage) of each strata ,as a proportion of the target population
-The number of participants needed from the subgroup are calculated(to ensure the sample is proportional to the sample population)
-Then individuals are randomly selected from each of the strata.
What are the strengths of stratified sampling?
As selection occurs from representative sub groups within in a population and involves random sampling, the selection is unbiased.
Therefore, the sample should be very representative of the target population-making it easier to generalize the findings of the study.
What are the limitations of stratified sampling?
-Dividing the population into stratums and then randomly selecting from each can be time consuming
-Detailed knowledge of the population characteristics are required for stratified samples which may not be available.
What is random sampling?
Every member of the target population has an equal chance of being selected.
How do you obtain random sampling?t
Lottery method-whereby each member of the population is assigned a number
All numbers are placed in a hat and the hat is shaken before drawing each number out the hat;until the required number of participants for the sample is required.
What are the strengths of random sampling?
-Each individual has the same chance of being. Therefore, sample is more likely to be representative of the wider target population. As, a result it is easier to generalize the findings to the wider target population so high population validity.
What are the limitations of random sampling?
-Still a chance that a certain type of people are selected from the target population however this decreases as the population increases.
-More time consuming to collect as the researcher needs to identify all the names of all the members of the target population before selecting a random sample from a wider group.
What is systematic sampling?
Participants are selected using a predetermined pattern or system
How is systematic sampling obtained?
Names of the members of the target population are organized into a list and then every nth person are used to create the sample. The interval is decided after the consideration of the target population and target size.
What are the strengths of systematic sampling
-Once the sampling system is applied, it increases the chances of getting biased (thus representative)sample.
What are the limitations of systematic sampling?
-Unbiased selection can only be ensured as long as the researcher has not intentionally biased the organization of the list/sampling system to include only certain types of people.
-The names of the target population are required which can be time consuming/difficult to obtain.
What is opportunity sampling?
Participants are selected by the researcher.
How is opportunity sampling obtained?
-The researcher decides on the type of participants needed and approaches and asks anyone who is available, willing and fits the research to participate.
This is done until sufficient numbers’ are obtained
What are the strengths of opportunity sampling?
It is relatively quick and convenient to collect an opportunity sample,as the researcher is not required to identify all the members of the target population, making it one of the most commonly used sampling methods.
