Chapter 6: Samples and observational studies — Vocabulary

Vocabulary flashcards covering key terms related to observational studies, sampling methods, study designs, and common biases from the lecture notes.

Observational study

A study that records data on individuals without attempting to influence responses; cannot confidently establish causation due to potential confounding.

Experimental study

A study that deliberately imposes a treatment and uses random assignment to control groups; allows control of influential factors and supports causal conclusions.

Population

The entire group of individuals of interest for a study.

Sample

The part of the population that is actually observed or studied.

Parameter

A numerical value that summarizes a characteristic of the population.

Statistic

A numerical value that summarizes a characteristic of a sample.

Simple random sample (SRS)

A sample in which every individual has the same probability of being chosen and all possible samples of size n are equally likely.

Randomness

A process that uses chance to select individuals, aiming to avoid bias in the sampling.

Bias

A systematic tendency for a study to favor certain outcomes.

Confounding

When the effects of two variables on a response cannot be distinguished from each other.

Undercoverage

Part of the population is systematically left out of the sampling frame.

Nonresponse

Selected individuals do not participate, potentially biasing results.

Wording effects

Differences in responses caused by how questions are phrased.

Response bias

Tendency for respondents to misreport or forget information, often amplified by the survey method.

Randomization

Assigning treatments to subjects by chance to reduce bias and confounding.

Stratified random sample

A probability sample that splits the population into strata and samples from each stratum to ensure known proportions.

Multistage sample

A sampling design that selects samples in successive stages, often within sampled units.

Primary Sampling Unit (PSU)

The first-stage unit chosen in a multistage sampling design (e.g., a county in a national survey).

Sample surveys

Observational studies relying on a random sample from the population, often used for polls and estimating incidence/prevalence.

Incidence

The rate at which new cases of a condition occur in a population over a period of time.

Prevalence

The proportion of individuals with a condition at a given point in time.

Case-control study

An observational study starting with cases (with the outcome) and controls (without) to look backward for exposures; retrospective and good for rare conditions.

Cohort study

An observational study that follows a group over time to compare exposures and outcomes; prospective and good for studying common conditions; often expensive.

Retrospective

Looking backward in time to study exposures relative to outcomes.

Prospective

Following subjects forward in time to observe future outcomes.

Aflatoxicosis

Poisoning caused by aflatoxins from fungi in damaged crops; studied in an outbreak example with case-patients and controls.

Placebo

An inactive treatment used as a control in experiments.

Form A / Form B (Wording effects)

Two versions of a question phrased differently to demonstrate how wording can shift responses and reveal wording effects.

Probability Sampling

individuals or units are randomly selected.

case-control studies

compares individuals with a specific condition (cases) to those without it (controls) to identify potential causes or risk factors.

cohort studies

follows a group of individuals over time to assess the development of outcomes based on various exposures or risk factors.

Quantative variable

A variable that can be measured on a numerical scalle

Qualitative variable

A variable that describes categories or qualities, rather than numerical values