Inappropriate comparisons – Jehovah’s witness surgery study

A new study about alternatives to blood transfusion, published recently in the Archives of Internal Medicine, seems to rest on a faulty premise.  The study compared outcomes from heart surgery for Jehovah’s Witnesses, who refuse blood transfusions, and are therefore prepared for surgery using strict blood conservation strategies before, during and after surgery, and other patients, about half of whom receive blood transfusions during surgery. The following report from The Melbourne Age is typical of how this has been reported in newspapers world wide:

JEHOVAH’S Witnesses, whose faith forbids them from blood transfusions, recover from heart surgery faster and with fewer complications than those who do get blood, in a study that may change thinking on current practice.

Patients who are Jehovah’s Witnesses had better survival rates, shorter hospital stays, fewer additional operations for bleeding and spent fewer days in the intensive care unit than those who received blood transfusions during surgery, a study in the Archives of Internal Medicine shows.

Interesting finding, but I am not convinced.  And not because there wasn’t an RCT and random assignment, but because of the comparison used.

Researchers in the study included 322 Jehovah’s Witness patients and 87,453 other patients who underwent heart surgery at the Cleveland Clinic from 1983 to 2011. All Jehovah’s Witness patients refused blood transfusions. In the other group, 38,467 did not receive transfusions while 48,986 did.

Within each group, we might expect there would be sicker and less sick patients.  And in the ‘other’ patients these are likely to be the ones who received a blood transfusion.  

What this study has done is to compare the outcomes for ALL of the Jehovah’s Witness patients with the sicker patients in the conventional treatment group.

 Jehovah’s Witness patients had an 86 per cent chance of survival at five years and a 34 per cent chance of survival 20 years after surgery, compared with 74 per cent at five years and 23 per cent at 20 years for non-Jehovah’s Witness patients who had transfusions.

Hmm.  So the average for this group was better than the average for the sickest half of the other group.  Hardly surprising. Or am I missing something?

Well maybe.  More detailed reporting at Heart/Wire ( shows there was a little more to the research design:

In the study, a total of 322 Jehovah’s Witnesses who underwent cardiac surgery at the Cleveland Clinic between January 1, 1983 and January 1, 2011 and who prospectively refused blood transfusions were included. They were compared with the same number of propensity-matched controls, with similar comorbidities, taken from 48 986 patients who underwent cardiac surgery during that period and did receive blood.

Even so, they were being compared to a group who all needed blood transfusions, which is only the case for half of all patients. So unless this reflects differences among surgeons (eg with some using transfusions for all of their patients and some for none) it is likely to indicate something about the nature of their condition or surgery which might make the groups not sufficiently comparable.

The actual article in Internal Medicine has much more detail about the propensity score matching technique and analytical techniques used to compare adverse effects. It also has some clearly stated limitations which are important:


Like all observational studies, our analyses have limitations. We chose to use propensity matching and to identify a control group that received transfusions to minimize selection and referral biases. Nonetheless, propensity methods can account only for those variables that were available and properly recorded. We did not record data on many Witness care-specific practice variables that may have changed over time. Thus, our analyses do not allow us to identify which practices may have contributed to the outcomes. Finally, Witnesses who came to our center and who were accepted by our surgeons likely represent a select group who might have been expected by their physicians to have better outcomes.

2 comments to Inappropriate comparisons – Jehovah’s witness surgery study

  • I’m pby missing something here, but I don’t see quite how the obvious altv explanation is ruled out, ie that it was the extra care with blood conservation, which almost certainly carries with it some extra care in infection control, the leading cause of post-operative morbidity/mortality across all OR patients.

    I’m sure the experimenters at Cleveland Clinic covered themselves against this, but how? Enlighten me!

    Michael Scriven

  • Patricia Rogers

    Good point, Michael. And the actual journal article does acknowledge this, without addressing it.

    I’ve edited the post to provide better links to this and to quote the stated limitations – none of which have been acknowledged in the widespread reporting on the study.