Statistical Sampling and Experimental Design Principles

Chapter 8: Sampling Designs and Methods

A basic random sampling design is a simple random sample (SRS) of size n. It consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected.

Voluntary Response Samples and Bias

A voluntary response sample consists of people who choose themselves by responding to a broad appeal. Voluntary response samples are biased because people with strong opinions are most likely to respond.

Stratified Random Sampling

To select a stratified random sample, first classify the population into groups of similar individuals, called strata. Then, choose a separate SRS in each stratum and combine these SRSs to form the full sample.

Undercoverage and Nonresponse

Undercoverage occurs when some groups in the population are left out of the process of choosing the sample. Nonresponse occurs when an individual chosen for the sample cannot be contacted or refuses to participate. A systematic pattern of incorrect responses in a sample survey leads to response bias.

Systematic Sampling Method

Systematic sampling is a type of probability sampling method in which sample members from a larger population are selected according to a random starting point and a fixed periodic interval.

Chapter 9: Experimental Design and Clinical Trials

Key Components of an Experiment

1. Experimental units or subjects
2. Explanatory factor (X): e.g., a drug
3. Treatments: e.g., drug or placebo
4. Treatment structure: One-way (1 factor) or two-way (2 factors)
5. Design structure: Completely Randomized Design (CRD)
6. Response variable (Y): e.g., number of pain episodes
7. Diagram or outline: Visual representation of the study

Confounding and Matched Pairs Design

Two variables (explanatory variables or lurking variables) are confounded when their effects on a response variable cannot be distinguished from each other. A matched pairs design is superior to a Completely Randomized Design (CRD) and is often considered the best approach; in a matched pairs design, we randomize within each pair.

Types of Clinical Trials

• Single-blind trial: In this trial, the patient is unaware of the treatment, but researchers are aware of it.
• Double-blind trial: Here, both the researchers and the patient are unaware of the treatment assignment.
• Randomized trial: Patients are distributed at random to avoid any bias in the results of the trial.
• Controlled trial: A comparator drug or placebo is used to determine the efficacy of the study drug.