Lect2 - CrossoverNotes - CHL 5225 H Crossover Trials The...

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

View Full Document Right Arrow Icon
CHL 5225 H Crossover Trials The Two-sequence, Two-treatment, Two-period Crossover Trial Definition A trial in which patients are randomly allocated to one of two sequences of treatments (either 1 then 2, or 2 then 1) so that within-patient differences can be used to compare treatments ( i.e. patients can be used as their own control) Patients must stop the first treatment, and either start the second or enter a wash- out period, at a predetermined point in time, which is the same for all patients CHL 5225 H Crossover Trials Period 1 2 1 2 Patient receives 1 Patient receives 2 Sequence (order) 2 1 Patient receives 2 Patient receives 1 2 1
Background image of page 1

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

View Full DocumentRight Arrow Icon
CHL 5225 H Crossover Trials Blocking Blocking may be employed to ensure roughly the same number of patients in each sequence Stratification Blocking within strata to balance for prognostic factors is usually not necessary since patients are their own contro since patients are their own control CHL 5225 H Crossover Trials Appropriate Diseases and Conditions Chronic, relatively stable Manifest as patient symptoms or disability Cyclical conditions such as nausea/vomiting with chemotherapy Appropriate Treatments Transient, non-curative Meant for symptom relief Short hal lives Short half-lives
Background image of page 2
CHL 5225 H Crossover Trials Appropriate Measurements Subjective – symptom scores, ratings of pain, etc Objective – strength Preference which treatment period did the patient prefe Preference – which treatment period did the patient prefer CHL 5225 H Crossover Trials Blinding Whenever possible patients, clinicians and observers should be blinded (masked) to treatment sequence and, if possible, unaware of the time at which the crossover from one treatment to the other occurs Other Design Features Possible “wash out” period between treatmen Possible wash-out period between treatment Possible baseline measurements prior to both treatment periods
Background image of page 3

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

View Full DocumentRight Arrow Icon
CHL 5225 H Crossover Trials Advantages Treatments are compared within patients, thereby the influence of patient factors (age sex disease severity) are “subtracted out” of patient factors (age, sex, disease severity) are subtracted out ; that is, the between-patient variance is removed, leading to: - smaller variances - increase power - smaller required sample sizes CHL 5225 H Crossover Trials Advantages  1 2 n N where n = number of patients required for a crossover trial N = number of patients required for a parallel groups trial, and = is the correlation between measurements made on the same patient Typically is between 0.3 and 0.6 For = 0.5 n1 N4
Background image of page 4
CHL 5225 H Crossover Trials Advantages Permits the use of preference data, which is particularly useful if a validated instrument for measuring outcome or disease status is not available CHL 5225 H Crossover Trials Disadvantages Short time frame does not permit the assessment of long term benefits and harms Crossover trial can be used because patients are more likely to consent Period effect – disease not a stable as expected
Background image of page 5

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

View Full DocumentRight Arrow Icon
CHL 5225 H Crossover Trials Disadvantages Bad press:
Background image of page 6
Image of page 7
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/23/2012 for the course CHL 5225H taught by Professor Andrewwillian during the Spring '12 term at University of Toronto- Toronto.

Page1 / 24

Lect2 - CrossoverNotes - CHL 5225 H Crossover Trials The...

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

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