Stat A Sampling & Bias Quiz

Sample Survey

A study that collects data from a sample to learn about the population from which the sample was selected. Examples include questionnaires and interviews.

Observational Study

A study that observes individuals and measures variables of interest but does not attempt to the influence responses. This is used to find a correlation between two variables and cannot determine cause and effect. Examples include a classroom observation or traffic inspections.

Experiment

A study in which researchers deliberately impose treatments on individuals to measure their responses. This tries to establish cause and effect. An example is a clinical trial.

Population

The entire group you want to study. An example would be all high school students.

Parameter

A characteristic of a population.

Census

A study that attempts to collect data from every individual in a population. This is difficult to achieve because it is inconvenient and requires extensive resources, time, and money.

Sample

A subset of a population. This is the group used to actually collect data. An example would be 300 high school students.

Statistic

A characteristic of a sample.

Representative

The sample should accurately reflect the characteristics of the population.

Sampling Variability

Statistics from different samples will vary from sample to sample.

Bias

When a statistical study consistently over or underestimates the value you were trying to measure.

Convenience Sampling

Gathering data from those who are easily accessible. Considered a bad sampling method because the sample will not be representative of the entire population. An example is polling individuals as they walk by.

Voluntary Response Sampling

People decide to join a sample by responding to a general invitation. Considered a bad sampling method because people who take the time to respond usually have extreme opinions. An example is when a TV host asks viewers to respond to an online poll, like in Dancing with the Stars.

Simple Random Sample (SRS)

A sampling method where every possible group of any size has an equal chance of being selected. This sampling method is considered better and often utilizes a random number generator (RNG) to select individuals.

Systematic Sampling

Individuals are selected at a fixed interval. An example is randomly selecting one person then selecting every 100th person in line at a concert. This is considered a better sampling method.

Stratified Random Sampling

The population is split into “separated” groups and the sample is made by picking a few people from each group. Considered a better sampling method.

Cluster Sampling

The population is split into “mixed” groups, and the overall sample is made-up of everyone from some of the groups. Considered a better sampling method.

Under – Coverage Bias

Because of the way the study is designed, a group of people are left out of the poll.

Non – Response Bias

People cannot be reached or choose not to respond to the poll.

Response Bias

Interviewer influences responses, often with the wording of questions or their appearance.