Variables, Sampling, and Study Design (PT)

Flashcards covering independent/dependent/modifying variables, sources of variance, populations vs samples, sampling methods (convenience, random, stratified, multi-stage, block), inclusion/exclusion criteria, and randomization concepts relevant to physical therapy research.

What is the independent variable in a research study?

The variable the researcher modifies/changes/manipulates; it can be one or multiple and is also called the intervention or predictor.

What is the dependent variable?

The outcome or endpoint that is measured; any level of measurement can be used as the dependent variable; its variance is influenced by the independent variable and other factors.

What are modifying variables?

Factors not manipulated but may affect the dependent variable; examples include exercise frequency (none, 2 days/wk, 4 days/wk, 6 days/wk) and nutrition/diet.

What are the three sources of variance in a dependent variable?

1) Effect of interest: variance due to the independent variable; 2) Moderating effect: variance due to other moderating variables; 3) Noise: variance due to measurement error.

Population vs. Sample

Population is the entire group of interest; a sample is a subset drawn from the population to study.

What is convenience sampling?

A fast, cheap non-probability sampling method; may have high response rate but is not representative of the population.

What is true random sampling?

A sampling method where every member of the population has a known, non-zero chance of selection; aims to produce a representative sample.

What is stratified random sampling?

Divides the population into strata based on characteristics, then randomly samples from each stratum; can be proportional to the strata’s size to reflect population structure.

What is multi-stage random sampling?

A sampling method that randomly samples from large clusters, then from smaller clusters within those clusters, and so on until individuals are selected.

Differentiate random sampling and random assignment

Random sampling is how you select the sample from the population; random assignment is how you allocate trial participants within the sample to control/experimental groups.

Clinical trials vs cohort studies

Clinical trials involve prospective assignment to an intervention; random assignment to groups is the most rigorous method, distinguishing them from observational cohort studies.

What is block randomization?

Random assignment conducted in blocks of predetermined size; ensures some balance in group sizes within each block; slots for control and treatment are filled from a fixed plan.

What is stratification in randomization?

Dividing participants into strata based on key characteristics and randomizing within strata to ensure balanced group characteristics.

What is adaptive randomization?

A randomization approach where allocation probabilities are adjusted during the trial to maintain balance on specified characteristics.

Inclusion criteria

The specific characteristics that define who is eligible to participate in the study; used to include appropriate participants.

Exclusion criteria

Specific characteristics that disqualify potential participants from participating; used to protect safety and study validity.

What does prospective assignment distinguish?

Prospective assignment to an intervention is what distinguishes clinical trials from observational studies; random assignment is the most rigorous form of this.