Biostat 215Clarifying the Causal Question

Thomas B. Newman, MD, MPH

Take-home message

In order to know how to get the answer, you need to be clear on the question

Often this means not only what question is being asked, but why it is important. What decisions might be affected by the results?

Examples Phototherapy for newborns TPA and death in stroke patients (Kurth)

– Different models addressed effect of TPA on different groups of patients

MSM for effect of ASA on CV mortality (Cook)– Total Effect ASA, including benefit from starting

after ASA after MI Hormone Replacement Therapy in nurses to

prevent CV mortality (Hernan)– Effect of starting vs being on HRT

New Example: Cerebral Palsy A group of nonprogressive disorders of

movement and posture caused by abnormal development of, or damage to, motor control centers of the brain.

Incidence about 2/1000 live births One (uncommon) cause is kernicterus. RQ: What are risk factors for cerebral palsy in

the Northern CA Kaiser Permanente Medical Care Program?

Late Impact of Getting Hyperbilirubinemia or photoTherapy

Late Impact of Getting Hyperbilirubinemia or photoTherapy (LIGHT) Study

Design: Historical cohort Subjects: 573,899 newborns born alive 1995-

2011 Predictor variables: hospital, prenatal,

perinatal variables from electronic record Outcome: CP, obtained from diagnoses in KP

Virtual Data Warehouse (VDW) or California Dept of Developmental Services (DDS), confirmed by chart review by child neurologist

?What variables should I include/control for?

Facility? Mother’s education? Gestational age? Birth weight?

I am interested in PREVENTABLE causes of CP

Particular interest in differences by facility, since there may be practice differences leading to differences in CP

Should I control for birth weight? Should I control for gestational age?

Depends on perspective, i.e., what interventions are envisioned

Pediatrics Obstetrics Public health

Starting with live births (especially ≥ 35 wks gestation) already reflects a pediatric perspective!

Starting with pregnancies reflects an obstetric prespective

Course review