{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

LECTURE 06 2011

# LECTURE 06 2011 - Outline of Stratification Lectures...

This preview shows pages 1–7. Sign up to view the full content.

Outline of Stratification Lectures Definitions, examples and rationale (credibility) Implementation Fixed allocation (permuted blocks) Adaptive (minimization) Rationale - variance reduction

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Stratification A procedure in which factors known to be associated with the response (prognostic factors) are taken into account in the design (e.g., randomization) Pre-stratification refers to a stratified design; post-stratification refers to the analysis
Pre- versus Post Stratification and Precision (Variance Reduction) As a general rule, the precision gained with pre- versus post-stratification is less than one might expect The gain in precision is greatest in small studies (where you need it the most) because the risk of chance imbalance is greater. Covariate adjustment for prognostic factors is usually carried out with regression (e.g., linear, logistic, or proportional hazards regression.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Stratification Can Increase Precision Simple versus stratified random sampling. Snedecor and Cochran note (p. 520): “If we form strata so that a heterogeneous population is divided into parts each of which is fairly homogeneous, we may expect a gain in precision over simple random sampling”. Ref. Snedecor and Cochran, Statistical Methods
Stratification Can Increase Precision Randomized block versus completely random design. Snedecor and Cochran note (p. 299): “Knowledge (about predictors or response) can be used to increase the accuracy of experiments. If there are a treatments to be compared,…first arrange the experimental units in groups of a , often called replications. The rule is that units assigned to the same replication should be as similar in responsiveness as possible. Each treatment is then allocated by randomization to one unit in each replication…Replications are therefore usually compact areas of land…This experimental plan is called randomized blocks.”

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Pre-stratification Does Not Matter.
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

### Page1 / 33

LECTURE 06 2011 - Outline of Stratification Lectures...

This preview shows document pages 1 - 7. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online