Biostatistics 2

What is a sample?

A subset of a population.

What is sampling?

The process of selecting a subset of a population to study.

Why do we sample populations?

Sampling is quicker, cheaper, and often more feasible than studying the entire population.

What is the most important factor in sampling?

Representativeness of the sample.

What is probability sampling?

Sampling where everyone in the population has a known, non-zero chance of selection.

What is a simple random sample?

Every member of the population has an equal chance of being selected.

What is a systematic sample?

Every nth element is selected from a list.

What is a stratified sample?

The population is divided into strata and a random sample is taken from each.

What is a cluster sample?

Entire clusters (e.g., schools) are randomly selected, then all or some within are surveyed.

What is multistage sampling?

Sampling that occurs in stages, often starting broad and becoming more specific.

Advantages of probability sampling?

Results are generalisable, fit statistical assumptions, and can be more precise.

Disadvantages of probability sampling?

Can require a complete list, be complex, and expensive.

What is non-probability sampling?

Sampling where the chance of selection is unknown and not random.

What is convenience sampling?

Using participants who are easiest to access.

What is quota sampling?

Like stratified sampling, but without random selection.

What is purposive sampling?

Researchers select participants based on their judgment.

What is snowball sampling?

Participants recruit other participants.

Advantages of non-probability sampling?

Low cost, quick, simple, and useful for exploratory research.

Disadvantages of non-probability sampling?

Not representative, higher risk of bias, cannot generalise findings.

What are mixed sampling designs?

A combination of judgmental and probability methods to enhance efficiency and representativeness.

What is validity in measurement?

The degree to which a tool measures what it is intended to measure.

What is internal validity?

The extent to which the findings apply to the study sample.

What is external validity?

The extent to which findings can be generalised to other populations.

What is reliability in measurement?

The consistency or repeatability of a measurement.

What causes poor reliability?

Random error.

What is random error?

Error that increases or decreases scores unpredictably. Reduces reliability.

What is systematic error?

Bias that skews results consistently in one direction.

What is selection bias?

Bias introduced from inappropriate selection or exclusion of participants.

What is information bias?

Bias resulting from measurement errors or misclassification.

What is confounding?

A mixing of effects between an exposure, the outcome, and a third variable.

Why can’t systematic error be corrected statistically?

Because it introduces consistent bias that distorts true findings