For cohort study what factors are related to exposure and thus might be

For cohort study what factors are related to exposure

This preview shows page 55 - 70 out of 71 pages.

For cohort study, what factors are related to exposure, and thus might be confounders? Who is in the population?
Image of page 55
Age (yrs) 21.9 22.4 Stress fracture (%) 40.0 39.1 Menses in past year 9.5 9.4 No. of lifetime menses 67.4 68.9 Oligo/amenorrhea (%) 35.8 30.0 Amenorrhea (%) 6.2 11.4 Oligomenorrhea (%) 29.6 18.6 Elevated EDI score (%) 21.0 30.0 Whole body BMD (g/cm 2 ) 1.10 1.11 Total hip BMD (g/cm 2 ) .97 .99 Spine BMD (g/cm 2 ) .99 .98 Total bone mineral content (g) 2146 2179 Height (inches) 65.2 65.4 Weight (lbs) 128.0 128.7 BMI (kg/ m 2 ) 21.2 21.1 Percent body fat 23.3 22.7 Calcium per day (mg) 1412 1401 control treatment Stress fracture study Baseline characteristics by randomization assignment
Image of page 56
Summary of events Might be presented as overall incidence rates. If events are heterogeneous (as with stress fractures), tabulate results.
Image of page 57
Stress Fracture 1 Diagnostic test Stress fracture 2 Study Area right tibial bone right tibial bone right tibial bone right tibial bone right tibial bone right tibial bone left tibial bone left tibial bone left tibial bone left tibial bone right foot right foot left third metatarsal right 4th metatarsal left cuboid navicular bone upper right femur right femoral neck 18 bone scan x-ray bone scan bone scan bone scan bone scan bone scan bone scan bone scan bone scan bone scan x-ray x-ray x-ray MRI bone scan MRI MRI right tibial bone right tibial bone right femur left foot 4 Boston Boston Boston Boston Stanford Michigan Boston Michigan Los Angeles Michigan Los Angeles New York Boston Stanford Stanford Stanford Los Angeles Stanford
Image of page 58
Evaluation of primary hypothesis Intention-to-treat analysis for RCT Primary exposure-event hypothesis for cohort study, adjusted for confounding
Image of page 59
Treatment (n=52) 6 fractures Control (n=70) 12 fractures Corresponding Kaplan-Meier curve
Image of page 60
Hazard Ratio (95% CI) Randomized to treatment .82 (0.30, 2.27) Corresponding HR
Image of page 61
Secondary analyses For RCT: any non-intention to treat analyses For RCT and cohort: evaluate other predictors; effect modification; subgroups
Image of page 62
Hazard Ratio (95% CI) Randomized to treatment .82 (0.30, 2.27) Randomized to treatment, on-protocol only (n=82) .63 (0.21, 1.92) Actually took OCs at least 1-month .41 (0.15,1.08) Per month on OCs .92 (0.85, 0.98) Time-dependent treatment variable, when on treatment .50 (0.18,1.40) **All analyses are stratified on site and menstrual status at baseline (amenorrheic, oligomenorrheic, or eumenorrheic), and adjusted for age and spine Z-score at baseline using Cox Regression. Hazard ratios for treatment variables
Image of page 63
<1800 g (n=15) 1800-2199 g (n=55) ≥2200 g (n=52) Kaplan-Meier estimates of stress fracture-free survivorship by BMC at baseline
Image of page 64
<800 mg/day (n=22) 800-1499 mg/day (n=63) 1500+mg/day (n=36) Kaplan-Meier estimates of stress fracture-free survivorship by levels of daily calcium intake at baseline
Image of page 65
Previous fracture (n=39) No previous fracture (n=83) Kaplan-Meier estimates of stress fracture-free survivorship by previous stress fracture
Image of page 66
Lowest quartile of lean mass Highest quartile of lean mass Middle two quartiles
Image of page 67
Image of page 68
Risk Factors Hazard Ratio (95% CI) History of menstrual irregularity prior to baseline 2.91 (0.81,10.43) BMC<1800g 3.70 (1.31, 10.46) Low calcium (<800 mg/d) 3.60 (1.12,11.59) Stress fracture prior to baseline 5.45 (1.48,20.08) Fat mass (per kg) 1.05 (0.91, 1.21) **All analyses are stratified on site and menstrual status at baseline, and adjusted for age and spine Z-score at baseline using Cox Regression.
Image of page 69
Image of page 70

You've reached the end of your free preview.

Want to read all 71 pages?

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture