Selecting Participants Flashcards
Is participant selection important?
The selection of research participants is a critical issue planning your research
The outcome of a study often depends on how you select your participants
What are the two aspects of a sample selection?
Population and sample
What is the population in a sample selection?
The large group of that you are interested in understanding
What is the sample in sample selection?
The small set of individuals who participate in the study
What is your goal of the sample selection?
Your goal is to be able to use data derived from the sample to infer something about the population
What is the cycle between the population and smaple?
Research begins with a general question about the a population
The population (all of the individuals of interest)
The sample is selected from the population
The sample (the specific set of individuals who participate in the research study)
- The actual research study is conducted with a sample
The results from the sample are generalized to the population
What is a representative sample?
A sample is representative if is has the same characteristics as the population
If your sample is not representative, you cannot generalize to the population very well
What is the sample vs the accessible population vs the target population
The sample: the individuals who are selected to participate in the research study
The accessible population: a portion of the target population consisting of individuals who are accessible to be recruited as participants in the study
The target population: The entire set of individuals who have the characteristics required by the researcher
What is the sample selection?
The way you choose who is going to participate in your research study
How you select a representative sample requires a lot of thought
What are some basic things you can do to ensure representativeness?
Use appropriate language in identifying your target population
- Use an appropriate sample size
- Use appropriate selection processes
How do you give an appropriate description of the population?
Be Explicit About the Sample!!
Instead of overgeneralizing, clearly state that your hypothesis applies to undergraduates from your specific university
- For example, instead of just saying “college students”, which is very general, be
specific!!
Undergraduate students at Stony Brook University who practice mindfulness
meditation will be less likely to get ill during the midterm period.
What is the law of large numbers?
A large sample will probably be more representative than a small sample
- A sample size of 25 to 30 individuals for each group or treatment condition is. a good target
What are two basic categories of sampling section?
Probability sampling
Non probability sampling
What is probability sampling?
The exact size of the population must be known and it must be possible to list all the individuals
- Each individual in the population must have a specified probability of selection
- The selection process must be unbiased; must be a random process
What is non probability sampling?
The odds of selecting a particular individual are completely unknown
What is simple random sampling?
Participants are selected from a list containing the total population
- Equality: each individual has an equal chance of selection
- Independence: choice of one individual does not influence or bias the probability of choosing another individual
Chance determines each selection
- Sampling with replacement: an individual selected for the sample is recorded as a sample member and then returned to the population (replaced) before the next selection
- Sampling without replacement: removes each selected individual from the population before the next selection is made
It is possible (although usually unlikely) to obtain a very distorted sample
What is systematic sampling?
Every nth participant is selected from a list containing the total population
A random starting position is
chosen
Violates the principle of independence
But, it ensures a high degree of representativeness
What is stratified random sampling?
The population is divided into subgroups (strata)
Equal numbers are randomly
selected from each of the subgroups
- Guarantees that each subgroup will have adequate
representation
- Overall sample is usually not
representative of the population
What is proportionate stratified sampling?
The population is subdivided
into strata
- Number of participants from each stratum is selected randomly
- The proportions in the sample correspond to the proportions in the population
Guarantees the sample will be perfectly representative of the population
- Some strata may have limited representation in the sample
What is a non probability sampling methods?
Convenience sampling
Quota Sampling
What is convenience sampling?
Individual participants are obtained by selecting those who are available and willing
An easy method for obtaining a sample
The sample is probably, most definitely BIASED
A weak form of sampling
The researcher makes no attempt to know the population or to use a random process in selection
What is quota sampling?
Another variation of a Convenience Sample BUT Subgroups are identified to be included
- Quotas are established for individuals to be selected through convenience from each subgroup
Allows a researcher to control the composition of a convenience sample
- The sample probably, most definitely is biased…
What does the acronym “WEIRD” describe?
Henrich et al. coined the acronym “WEIRD” to describe
samples comprised of:
- Western
- Educated
- Industrialized
- Rich
- Democratic Individuals
How does the acronym “WEIRD” lead to bias?
Most Psychology findings, which come from convenience samples, are presented as applying to all humans
However, these samples are biased and likely do not apply to people from radically different backgrounds….
