Selecting Research Participants Flashcards
What is the difference between a sample and a population?
Sample - a set of individuals selected from a population meant to represent a population
Population - the entire set of individuals of interest to the researchers
What is a target population?
A group defined by a researcher’s specific interests
Why might target populations not be easily accessible?
The researcher may not have access to most people that are able and willing to be recruited for the study
What is an accessible population?
An easily accessible segment of the target population which most researchers use to select a sample from
What is the extent to which the characteristics of a sample accurately reflect the characteristics of a population called?
Representiveness
To generalize the results of a study to a population, what would a researcher need to select?
A representative sample
What is the most major threat to selecting a representative sample?
Bias - a biased sample has noticeable different characteristics from the population.
What is the type of bias where individuals are selected in a manner that increases the possibility of obtaining a biased sample?
Selection bias (aka sample bias)
In the field of statistics, what is the principle of the law of large numbers?
The larger the sample size, the more accurate the values are to the population
What is the process of selecting individuals for a study called?
Sampling
Sampling methods fall under two basic categories. What are they?
- Probability sampling
- Nonprobability sampling
What are the 3 conditions of probability sampling?
- Exact size of the population must be known
- Each individual must have a specified probability of selection
- Selection must be a random process and each individual has an equal chance of being chosen
In nonprobability sampling, the population and individual probabilities are not completely known. How does the sampling method base itself on to reduce bias?
Based on factors like common-sense or ease, effort towards representativeness
What type of sampling is the starting point for most probability sampling techniques?
Simple random sampling
What are the 3 steps of simple random sampling?
- Clearly define the population from which a sample will be chosen from
- List all members of the population
- Use a random process to select individuals from the list
What are the 2 principal method of random sampling and how do they work?
- Sampling with replacement - an individual selected returns to the population after being recorded, so that the odds of being chosen are consistent throughout selection, ensuring independent selections
- Sampling without replacement - and individual selected is removed from the population, changing the odds of being chosen throughout selections, and independent selections are not produced
What is a concern about simple random sampling?
Because chance determines each selection, it is possible, albeit unlikely, to obtain a distorted and non-representative sample
What is systematic sampling?
Similar to simple random sampling, obtaining a sample by selecting every nth participant from a list containing the total population
Why is systematic sampling less random than simple random sampling?
The principle of independence is violated
What is stratified random sampling?
A sampling technique that identifies specific subgroups to be included into the sample, then selecting equal-sized random samples from those specific subgroups to make up a sample
Why isn’t stratified random sampling considered totally random?
All individuals in the population are not equally likely to be selected, as the subgroup sizes are often different in size
What is proportionate (stratified) random sampling?
A sampling technique that identifies specific subgroups and proportionately selects from them to make up a sample
What is cluster sampling?
A sampling technique that involves random groups as opposed to random individuals from a population
Why is convenience sampling considered weak?
It does not require knowledge of the population nor does it use a random process for selection, therefore the individuals are unlikely to be representative of the population
What is the most commonly used sampling in behavioural science and how does it work?
Convenience sampling - researchers simply select individuals who are able and willing to respond, as they are easy to get
What 2 strategies do researchers use to strengthen the flawed practice of convenience sampling?
- Attempt to ensure samples are reasonably representative and not strongly biased
- Provide a clear description of how the sample was obtained and who the participants were
What nonprobability sampling method involves identifying specific subgroups to be included in the sample and then establish quotas for individuals to be sampled from each group?
Quota sampling
If a researcher does not know the entire list of people in a population, and wants to represent equally sized groups in a sample, what method should be used?
Quota sampling
