This piece of “reportage” from the SMH is typical of the coverage of a paper summarising research done by obstetricians and published in the Medical Journal of Australia:
Private birth has benefits for babies
Babies born to women in private hospitals are less likely to need resuscitation at birth or admission to intensive care than those born in a public hospital, a national study has found.
Obstetricians say the study, published in the Medical Journal of Australia, debunks widespread criticism of the high intervention rates for women in private hospitals.
The authors, from the Australian National University and University of NSW, say the findings challenge the long-held orthodoxy that increased rates of obstetric intervention, such as caesarean and induction, are “bad” for women and their babies.
Only as an afterthought does the SMH article mention that the study is comparing apples and oranges (although the information they highlight is actually more like comparing apples with cheese).
Neonatal death rates were 1 in 1000 in private hospitals and 3 in 1000 in public hospitals. The study took into into account that public hospitals deal with a higher proportion of riskier births. Younger women, smokers, indigenous women, rural women and women with medical conditions such as hypertension or diabetes are more likely to be cared for under the public system.
Women booked to deliver in a public hospital because serious adverse outcomes were predicted were excluded from the study
The second paragraph above seems to have been included to make it look like the populations of public and private patients have actually been matched for this study, when in fact only one of many criteria that make the two populations different is mentioned. How exactly did the study “take into account” the population differences other than by excluding the “predicted serious adverse outcomes”? Did they match for socioeconomic status, which is kinda crucial given that middle-class and wealthier populations are healthier than poorer populations anyway?
It doesn’t surprise me one little bit that a middle-class and wealthier population is going to have healthier babies, because they have the privilege of discretionary income to devote to supplementary aspects of pregnancy, while most people who don’t have private healthcare do not (one of the reasons they don’t have private healthcare, in fact).
To bring Bayes’ Theorem actually into the post: the researchers have taken a narrowly sampled sub-population already predisposed to having healthier babies, compared them to a far more broadly sampled population not generally sharing that same predisposition, and having discovered that their subpopulation does indeed have healthier babies, have then concluded that it is actually something they are doing to this subpopulation that is making a crucial difference. They have ignored nearly all the prior and conditional probability factors in their analysis of two populations.
For example, say that we have 100 women each from private and public hospital populations.
- In the private hospital population, no births are excluded from this study due to predicted serious adverse birth outcomes because those women have already been referred to the specialty team at the public teaching hospital, because these women are receiving frequent prenatal health checks.
- In the public hospital, as they have indicated, there are a certain number of predicted serious adverse birth outcomes referred prior to delivery, so that perhaps 5/100 births are excluded due to this.
- in the public hospital, many women have not been having regular prenatal health checks due to affordability or remoteness issues, so often no adverse birth outcome has been predicted even though they belong to an at-risk population as described above – “younger women, smokers, indigenous women, rural women and women with medical conditions such as hypertension or diabetes” – these women without predictions of trouble are not excluded from this study – let’s say 5/100 are only discovered to be having adverse birth outcomes after they have started delivery.
- Of the 100 women in the private hospital, a large number will be undergoing planned pregnancies where they built their bodies up for gestation while pre-pregnant by taking supplements such as folic acid and quitting smoking and drinking. These women are in the lowest risk category for birth complications.
- Of the 100 women in the public hospital, many of the poorest women will be undergoing an unplanned pregnancy (due to difficulties obtaining affordable reliable contraception) and will not have had the opportunity to stop drinking/smoking or take dietary supplements before the time of conception, and may have continued drinking/smoking for weeks or even months afterwards until they discovered that they were pregnant. Again, as they are less likely to have frequent prenatal checks and thus less likely to become “predicted adverse birth outcomes” – their adverse outcome will be a nasty surprise, and will be included in the study. Let’s say another 5/100 births fall into this category.
I’m sure you can all think of a few other aspects where the public hospital population has a higher prior probability of adverse birth outcomes no matter what intervention obstetricians put in place.
Sure, I’ve built in some assumptions above, and if my suggested rates are way off I’d be grateful for better information (especially if the ratio of unpredicted to predicted serious adverse outcomes is horribly inverted). But I hope you can see that excluding only “predicted” serious adverse outcomes ignores the glaring disparity between one population containing a large number of higher-obstetric-risk women who don’t come into the hospital’s radar until after they have presented for delivery, while the other population does not, and presenting the two populations as directly comparable.
Have peer review committees just given up on actually including a statistician these days? or do the statisticians need to do more sociology classes?
There are still middle-class women who have an ideological commitment to public healthcare, and who have all the health advantages that discretionary income provides. Let’s see a direct comparison between their birth outcomes compared to the private hospital birth outcomes, shall we? And just to placate the feminists, let’s also include maternal health outcomes in our study, beyond just the incidence of perineal tears (which tend to heal better than perineal cuts anyway) – how have the middle-class public hospital mothers who had low-intervention births recovered two weeks, four weeks, six weeks after birth? compared to the private hospital mothers recovering from their higher rates of abdominal surgery?