EXAMPLE E9.13 Blood clots in immobilized patients Patients immobilized for a sub

Q: EXAMPLE E9.13 Blood clots in immobilized patients Patients immobilized for a sub

Drug Placebo complication 42 73 No complication 1476 1400 1518 1473 For Placebo, Risk= 73/1473=0.0496 or 4.96% Odds =0.0496/(1-0.0496) =73/1400 =0.0521 Compared to drug group, risk and odds are more for the placebo group. Drug Placebo complication 42 73 No complication 1476 1400 1518 1473

ID: 3128043 • Letter: E

Question

EXAMPLE E9.13 Blood clots in immobilized patients Patients immobilized for a substantial amount of time can develop deep vein throm bosis (DVT), a blood clot in a leg or pelvis vein. DVT can have serious adverse health efects and can be difficult to diagnose. On its website, drug manufacturer Pfizer reports the outcome of a study looking at the effectiveness of the drug Fragmin (dalteparin) in preventing DVT in immobilized patients. Of the 1518 randomly chosen immobilized patients given Fragmin, 42 experienced a complication from DVT (the remaining 1476 patients did not ). 2 The proportion of patients experiencing DVT complications is 42/1518 = 0.0277, or 2.77%. We can use this information to compute the risk and odds of experiencing DVT complications for immobilized patients treated with Fragmin : risk = 0.0277, or 2.77% odds = 0.0277/(1 - 0.0277) = 42/1476 = 0.0285 The odds of experiencing DVT complications among immobilized patients given Frag min are 42:1476or about 135. That is, for every such patient experiencing a DVT complication, about 35 do not experience a DVT complication. E The numerical values for the risk and odds in this example are very close, 0.277 and 0.0285. In general, when the sample size is very large and the undesirable event not very frequent, risk and odds give similar numerical values. In other situations, risk and odds can be very different.

Explanation / Answer

Drug

Placebo

complication

No complication

1476

1400

1518

1473

For Placebo,

Risk= 73/1473=0.0496 or 4.96%

Odds =0.0496/(1-0.0496)

=73/1400

=0.0521

Compared to drug group, risk and odds are more for the placebo group.