Table 1. Calculation of the odds ratio... | American Society of Hematology

Table 1.

Calculation of the odds ratio for studies investigating the relationship between allogeneic blood transfusion and cancer recurrence or postoperative infection

Group	Adverse outcome: cancer recurrence or postoperative infection		Totals
Group	Occurring	Not occurring	Totals
Exposed to allogeneic transfusion^*	a	b	a + b
Not exposed to allogeneic transfusion^†	c	d	c + d
Totals	a + c	b + d	n^‡

Group	Adverse outcome: cancer recurrence or postoperative infection		Totals
Group	Occurring	Not occurring	Totals
Exposed to allogeneic transfusion^*	a	b	a + b
Not exposed to allogeneic transfusion^†	c	d	c + d
Totals	a + c	b + d	n^‡

Odds of an adverse outcome in those exposed to allogeneic transfusion: [a / (a + b)] / [b / (a + b)] = a / b

Odds of an adverse outcome in those not exposed to allogeneic transfusion: [c / (c + d)] / [d / (c + d)] = c / d

Odds ratio = \frac{Odds of an adverse outcome in those exposed to allogeneic transfusion}{Odds of an adverse outcome in those not exposed to allogeneic transfusion} = \frac{\frac{a}{b}}{\frac{c}{d}} = \frac{ad}{bc}

Treatment arm (patients prospectively randomized to receive transfusion of allogeneic WBCs) in RCTs, or treatment group (patients having transfusion) in observational cohort studies.

†

Control arm (patients prospectively randomized to receive transfusion of autologous or WBC-reduced allogeneic RBCs) in RCTs, or control group (patients not having transfusion) in observational cohort studies.

‡

n = a + b + c + d; a, b, c, and d are the 4 counts of a 2 × 2 contingency table.54

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Odds of an adverse outcome in those exposed to allogeneic transfusion: [a / (a + b)] / [b / (a + b)] = a / b
Odds of an adverse outcome in those not exposed to allogeneic transfusion: [c / (c + d)] / [d / (c + d)] = c / d

$Odds ratio = \frac{Odds of an adverse outcome in those exposed to allogeneic transfusion}{Odds of an adverse outcome in those not exposed to allogeneic transfusion} = \frac{\frac{a}{b}}{\frac{c}{d}} = \frac{ad}{bc}$

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