INTRODUCTION TO STATISTICS
DESCRIPTIVE STATISTICS AND DATA
ANALYSIS STUDY GUIDE 2026
◉ Stratified Random Sample
Answer: A random sampling method where individuals are
separated into homogeneous groups, then simple random samples
are taken within each group.
◉ Stratum/Strata
Answer: The homogeneous groups in a stratified random sample. All
individuals in each stratum have something in common, and we
would like to see how that affects the outcome of the sample.
◉ Cluster Sample
Answer: A sampling method where the population is separated into
groups, typically geographically, and a random selection of clusters
is made. Each individual in the cluster becomes part of the sample.
◉ Clusters
Answer: Smaller subgroups of the population, not necessarily
similar in any way besides all being together in one
place, making the individuals easier to sample together.
, ◉ Multi-stage sampling
Answer: A sampling design which combines elements of cluster
sampling, stratified random sampling, and simple random sampling.
It "zooms in" on smaller areas to sample so that sampling becomes
more feasible.
◉ Observational Study
Answer: A type of study where researchers can observe the
participants, but not affect the behavior or outcomes in any way.
◉ Retrospective Study
Answer: A study that observes what happened to the subjects in the
past, in an effort to understand how they became the way they are in
the present.
Researchers look to the past to see what has already happened; also
known as a case-control study.
◉ Prospective Study
Answer: A study that begins by selecting participants, tracking them,
and keeping data on the subjects as they go into the future.
DESCRIPTIVE STATISTICS AND DATA
ANALYSIS STUDY GUIDE 2026
◉ Stratified Random Sample
Answer: A random sampling method where individuals are
separated into homogeneous groups, then simple random samples
are taken within each group.
◉ Stratum/Strata
Answer: The homogeneous groups in a stratified random sample. All
individuals in each stratum have something in common, and we
would like to see how that affects the outcome of the sample.
◉ Cluster Sample
Answer: A sampling method where the population is separated into
groups, typically geographically, and a random selection of clusters
is made. Each individual in the cluster becomes part of the sample.
◉ Clusters
Answer: Smaller subgroups of the population, not necessarily
similar in any way besides all being together in one
place, making the individuals easier to sample together.
, ◉ Multi-stage sampling
Answer: A sampling design which combines elements of cluster
sampling, stratified random sampling, and simple random sampling.
It "zooms in" on smaller areas to sample so that sampling becomes
more feasible.
◉ Observational Study
Answer: A type of study where researchers can observe the
participants, but not affect the behavior or outcomes in any way.
◉ Retrospective Study
Answer: A study that observes what happened to the subjects in the
past, in an effort to understand how they became the way they are in
the present.
Researchers look to the past to see what has already happened; also
known as a case-control study.
◉ Prospective Study
Answer: A study that begins by selecting participants, tracking them,
and keeping data on the subjects as they go into the future.
