LECTURE 18 2011

LECTURE 18 2011 - Sample Size Estimation 1. Continuous...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Sample Size Estimation 1. Continuous response variable Parallel group comparisons Comparison of response after a specified period of follow-up Comparison of changes from baseline Crossover study 2. Success/failure response variable Impact of non-compliance, lag Realistic estimates of control event rate (Pc) and event rate pattern Use of epidemiological data to obtain realistic estimates of experimental group event rate (Pe) 3. Time to event designs and variable follow-up
Background image of page 1

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

View Full DocumentRight Arrow Icon
Usual Situation for “Time-to-Event” Clinical Trials 1. Recruitment extends over several months or years. 2. Trial design usually specifies minimum period of follow-up for all patients. 3. Total trial duration = Recruitment period + minimum follow-up period following enrollment. 4. Not all patients experience primary endpoint (censored observations). 5. Trial is terminated on a common closing date that either corresponds to minimum follow-up specified or planned no. of events.
Background image of page 2
Usual Situation (cont.) 6. Patients are followed for a variable length of time as a consequence of recruitment period and common closing date. 7. Time to event methods (e.g., Cox models and log rank statistics are used to compare groups) 8. Sample size based on tests of proportions may not be appropriate as proportion with event is considered over a variable follow-up period, not fixed (need to consider length of follow-up). Note: For studies in which the study duration is short compared to average event time (e.g., survival time), sample size using proportions is similar to that using time to event . When this is not the case, using proportions generally results in a larger sample size than considering time to event.
Background image of page 3

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

View Full DocumentRight Arrow Icon
Reasons for Censoring End of follow-up (administrative) Lost to follow-up (bias is a concern) Competing event (e.g., death from an accident in a CVD study; in some cases bias is also a concern)
Background image of page 4
Typical Enrollment in Trial x x x 1 2 3 4 5 6 7 8 9 April 30 1977 x x A B B A B B A A A B 1 2 3 4 5 6 7 8 9 10 Patient Acc. No. Treatment End of Study x – Death – Censored Calendar Time from Start of Study (Months) 0
Background image of page 5

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

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/21/2011 for the course PUBH 7420 taught by Professor Ph7420 during the Spring '07 term at Minnesota.

Page1 / 25

LECTURE 18 2011 - Sample Size Estimation 1. Continuous...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online