Sampling (Part II)

Weighted Sampling

A random sampling method where some items are given greater chances of being selected, like a lottery with different ticket counts.

Stratified Random Sampling

The population is divided into subgroups (strata), and a simple random sample is drawn from each stratum.

Cluster Sampling

Items are selected in groups or clusters, often used when the population is too large or spread out for simple random sampling.

statistical theory, random variation, systematic bias

Advantage of a Simple Random Sampling is that it provides a foundation for _________________ because sample differences arise only from ________________, not ________________.

One-Sample Experiment

An experiment involving one population where a single sample is drawn to study one characteristic.

Like, tensile strength from one process.

Multi-Sample Experiment

Involves two or more populations, a sample is drawn from each to make comparisons between them.

Factorial Experiment

An experiment where two or more factors are varied systematically, and a simple random sample is drawn for each factor combination.

Controlled Experiment

Experiment type where the experimenter controls factor levels to study their effect on a response, allowing reliable cause-and-effect conclusions.

Observational Study

The experimenter observes existing conditions without controlling factors;

weaker for determining cause and effect.

Example of a Controlled Experiment

A chemical engineer varies reagent and catalyst concentrations to observe yield changes.

Example of an Observational Study

Comparing lung cancer rates between smokers and non-smokers without controlling who smokes.

Numerical (Quantitative) Data

Data that represents measurable quantities such as “How much” or “How many”

Categorical (Qualitative) Data

Data that classifies items into categories or groups rather than numerical values.

Example of a Quantitative Data

Failure pressure and thickness of wood panels.

Example of a Qualitative Data

Sheathing type and wood species of the same panels.