PROGNOSIS Cohort studies

Distressed 3100g male newborn At delivery Limp, cyanotic, no spontaneous respiratory effort, heart rate 50 beats/min. Suction - no grimace, cough or sneeze Vigorous resuscitation At 1 minute: Apgar score = 1 At 5 minutes: Apgar score = 2, 110 beats/min. At 10 minutes: Apgar score = 3

APGAR SCORE FOR EVALUATION OF NEONATAL ASPHYXIA Adapted from Apgar V, James LS. Am J Dis Child 1962; 104:419

Distressed 3100g male newborn At delivery Limp, cyanotic, no spontaneous respiratory effort, heart rate 50 beats/min. Suction - no grimace, cough or sneeze Vigorous resuscitation At 1 minute: Apgar score = 1 At 5 minutes: Apgar score = 2, 110 beats/min. At 10 minutes: Apgar score = 3 PROGNOSIS??

Objectives Cohort study describe structure and analysis interpret and calculate relative and absolute measures of effect identify potential for bias

RCT / Cohort

Apgar scores as predictors of chronic neurologic disabilities Nelson KB, Ellenberg JH, Pediatrics, 1981; 68: infants followed for 7 years. Apgar scores recorded at 1 and 5 minutes (and for infants with AS<8 at 10, 15 & 20 minutes) Histories recorded at 4, 12, 18 months and then yearly to age 7

Relationship between 10-minute Apgar scores and risk of death in the 1st year of life among children with birth weight of at least 2500g Risk in ‘exposed’ = ? Risk in ‘less’ exposed= ? Relative risk = ? Risk difference = ? Attributable risk % = RD/ R(exp) = ?

Relationship between 10-minute Apgar scores and risk of death in the 1st year of life among children with birth weight of at least 2500g Risk in exposed = 42 / 122 = = 34.4% Risk in less exposed = 43 / 345 = = 12.5% Relative risk = / = 2.8 Risk difference = = 21.9% Attributable risk % = RD / R(exp) = / = 64%

55% of cerebral palsy (CP children had 1 minute scores >= 7 99 survivors with scores (at 10, 15 or 20 minutes, all birth weights) 80% free of major handicap 12 had CP 11 mentally retarded, 1 normal 10 had had seizures on day of birth 1 in 8 asphyxiated neonates have CP and developmental delays << 1in 8 of those without seizures

What is key difference between RCT and cohort study? RCT Random allocation of intervention/exposure by investigator Cohort Self selection of exposure/risk factor