PSYCH 505 Final Exam Study Guide Questions with Correct Answers Latest Update
2026/2026
Describe the difference between probability and non-probability sampling. - Answers
PROBABILITY: KNOWN chance of being selected NON-PROBABILITY: UNKNOWN chance of
being selected
Sampling unit - Answers -unit of analysis based on research objectives
-basic unit for sampling
-ex. schools in educational psychology
Population - Answers entire group under study as specificied in the research objectives
-ex. US Census population
-ex. 2022 on-campus MAPP cohort
Sample - Answers subset of the population that should represent the entire group --> used to
estimate population values
-ex. 2022 on-campus MAPP cohort OUT OF masters students at USC
Census - Answers accounting of everyone in the population
**mutually exclusive from a sample
Sampling error - Answers -any error in a survey that occurs because a sample is used
-difference between the population value and the sample estimate (usually unknown)
CAUSES
-method of sample selection
-sample size (the larger the sample size, the closer you get to the population, smaller sampling
error)
,Sampling frame - Answers master list of all the members of the population
Sampling frame error - Answers over/under-representation of true population in the sampling
frame
-ex. SC Edison: particularly hot month in September, new users --> there is an error because they
came into sampling frame after August when it was measured
Random sample - Answers when every member (sampling unit) of the population has an equal
chance, or probability, of being selected into the sample
Non-probability sample - Answers when every member (sampling unit) of the population have
not been enumerated and do not have an equal chance of being selected
Probability sampling - Answers -random sample
-key component of study design
-all members of the population have been enumerated
-chance selection can be expressed as a probability
-probability samples are based on random sampling
-only probability samples will result in representative samples
-probability samples have high generalizability
EXAMPLE
-USC students, everyone has one email address associated with USC
-can be selected within THIS POPULATION because there is only 1 email
-know the probability of being accepted into sample has high generalizability
Non-probability sample - Answers all members (sampling unit) of the population have NOT been
enumerated and do not have an equal chance of being selected
Non-probability sampling - Answers -non-probability sample
-non-generalizable
-low to no external validity
, USED BECAUSE
-faster than probability sampling
-cheaper than probability sampling
-generalizability may not be important
-some info is better than no info
QUITE COMMON IN MARKET RESEARCH/PSYCHOLOGY STUDIES
EXAMPLE
-multiple Amazon accounts
-not 2 individuals
-having multiple emails in 1 system
What are the 4 probability sampling methods? - Answers 1. simple random sampling
2. Nth selection (systematic sampling)
3. cluster sampling
4. stratified sampling
Simple random sampling - Answers DEFINITION: randomly sample some number of individuals
to participate in a study from the population
-random digit dialing (RDD) --> not what it used to be --> former gold standard
-best for generalizability/representativeness
Nth selection (systematic sampling) - Answers -can be biased
-best for paper/non-computerized lists --> pick every 5th person
-must divide the list into equal Nth intervals
-Nth intervals = (sample size/list length)
2026/2026
Describe the difference between probability and non-probability sampling. - Answers
PROBABILITY: KNOWN chance of being selected NON-PROBABILITY: UNKNOWN chance of
being selected
Sampling unit - Answers -unit of analysis based on research objectives
-basic unit for sampling
-ex. schools in educational psychology
Population - Answers entire group under study as specificied in the research objectives
-ex. US Census population
-ex. 2022 on-campus MAPP cohort
Sample - Answers subset of the population that should represent the entire group --> used to
estimate population values
-ex. 2022 on-campus MAPP cohort OUT OF masters students at USC
Census - Answers accounting of everyone in the population
**mutually exclusive from a sample
Sampling error - Answers -any error in a survey that occurs because a sample is used
-difference between the population value and the sample estimate (usually unknown)
CAUSES
-method of sample selection
-sample size (the larger the sample size, the closer you get to the population, smaller sampling
error)
,Sampling frame - Answers master list of all the members of the population
Sampling frame error - Answers over/under-representation of true population in the sampling
frame
-ex. SC Edison: particularly hot month in September, new users --> there is an error because they
came into sampling frame after August when it was measured
Random sample - Answers when every member (sampling unit) of the population has an equal
chance, or probability, of being selected into the sample
Non-probability sample - Answers when every member (sampling unit) of the population have
not been enumerated and do not have an equal chance of being selected
Probability sampling - Answers -random sample
-key component of study design
-all members of the population have been enumerated
-chance selection can be expressed as a probability
-probability samples are based on random sampling
-only probability samples will result in representative samples
-probability samples have high generalizability
EXAMPLE
-USC students, everyone has one email address associated with USC
-can be selected within THIS POPULATION because there is only 1 email
-know the probability of being accepted into sample has high generalizability
Non-probability sample - Answers all members (sampling unit) of the population have NOT been
enumerated and do not have an equal chance of being selected
Non-probability sampling - Answers -non-probability sample
-non-generalizable
-low to no external validity
, USED BECAUSE
-faster than probability sampling
-cheaper than probability sampling
-generalizability may not be important
-some info is better than no info
QUITE COMMON IN MARKET RESEARCH/PSYCHOLOGY STUDIES
EXAMPLE
-multiple Amazon accounts
-not 2 individuals
-having multiple emails in 1 system
What are the 4 probability sampling methods? - Answers 1. simple random sampling
2. Nth selection (systematic sampling)
3. cluster sampling
4. stratified sampling
Simple random sampling - Answers DEFINITION: randomly sample some number of individuals
to participate in a study from the population
-random digit dialing (RDD) --> not what it used to be --> former gold standard
-best for generalizability/representativeness
Nth selection (systematic sampling) - Answers -can be biased
-best for paper/non-computerized lists --> pick every 5th person
-must divide the list into equal Nth intervals
-Nth intervals = (sample size/list length)
