Glossary
Bias
Any systematic error in a study design or data collection that causes the sample results to differ systematically from the true population parameter. It can lead to inaccurate conclusions.
Example:
If a survey about internet usage is only conducted via landline phones, it would introduce bias because it systematically excludes individuals who only use cell phones or have no phone.
Census
A study that collects data from every individual in the entire population. It aims to gather complete information rather than relying on a sample.
Example:
The U.S. government conducts a census every ten years to count every person living in the country, gathering demographic information from the entire population.
Confounding
Occurs when the effects of two or more variables on a response variable cannot be distinguished from each other. It makes it difficult to determine which variable is truly causing an observed effect.
Example:
If a study finds that people who drink more coffee tend to live longer, but also notes that coffee drinkers often exercise more, then exercise could be a confounding variable, making it hard to say if coffee or exercise causes longer life.
Experiment
A study design where researchers intentionally impose a treatment on individuals to observe their responses. It allows for the establishment of cause-and-effect relationships.
Example:
To test a new pain medication, researchers randomly assign patients to receive either the new drug or a placebo, then compare their pain relief, making this an experiment.
Generalizability
The extent to which the findings from a study's sample can be accurately applied or extended to the larger population from which the sample was drawn. It depends heavily on the sampling method.
Example:
If a study on a new teaching method was conducted only in private schools, its generalizability to public school students might be limited.
Observational Study
A study where researchers observe and measure variables of interest without manipulating or imposing any treatments. It aims to describe a group or situation.
Example:
A study tracking the dietary habits and health outcomes of a group of people over several years to see if certain foods are associated with specific diseases is an observational study.
Population
The entire group of individuals or instances about which we want to gain information. It represents the complete set of data points of interest.
Example:
If a researcher wants to study the average height of all high school students in the United States, then all high school students in the U.S. constitute the population.
Prospective Study
A type of observational study that follows individuals forward in time, collecting data as events unfold. It tracks participants to observe future outcomes.
Example:
A long-term study that enrolls healthy individuals and monitors their lifestyle choices and health status over decades to see who develops heart disease is a prospective study.
Random Sampling
A method of selecting a sample from a population where every individual has an equal chance of being chosen. This technique helps ensure the sample is representative and reduces bias.
Example:
To select students for a school survey, putting all student names into a hat and drawing out 100 names is an example of random sampling.
Retrospective Study
A type of observational study that looks back in time to collect data on past events or exposures. It uses existing records or participant recall.
Example:
Researchers reviewing medical records from the last 20 years to identify common factors among patients who developed a rare disease are conducting a retrospective study.
Sample
A smaller, representative subset of individuals selected from the population. Data is collected from the sample to make inferences about the larger population.
Example:
To estimate the average height of all high school students, a researcher might measure the heights of 500 randomly selected high school students, forming a sample.
Sample Survey
A type of observational study that collects data from a sample of individuals, typically through questionnaires or interviews, to gather information about a population's characteristics or opinions.
Example:
A polling organization contacts a random group of 1,500 registered voters to gauge their opinions on an upcoming election, which is a classic sample survey.