Thesis Thursday: Matthew Quaife

On the third Thursday of every month, we speak to a recent graduate about their thesis and their studies. This month’s guest is Dr Matthew Quaife who has a PhD from the London School of Hygiene and Tropical Medicine. If you would like to suggest a candidate for an upcoming Thesis Thursday, get in touch.

Using stated preferences to estimate the impact and cost-effectiveness of new HIV prevention products in South Africa
Fern Terris-Prestholt, Peter Vickerman
Repository link

Stated preferences for what?

Our main study looked at preferences for new HIV prevention products in South Africa – estimating the uptake and cost-effectiveness of multi-purpose prevention products, which protect against HIV, pregnancy and STIs. You’ll notice that condoms do this, so why even bother? Condom use needs both partners to agree (for the duration of a given activity) and, whilst female partners tend to prefer condom-protected sex, there is lots of evidence that male partners – who also have greater bargaining power in many contexts – do not.

Oral pre-exposure prophylaxis (PrEP), microbicide gels, and vaginal rings are new products which prevent HIV infection. More importantly, they are female-initiated and can generally be used without a male partner’s knowledge. But trials and demonstration projects among women at high risk of HIV in sub-Saharan Africa have shown low levels of uptake and adherence. We used a DCE to inform the development of attractive and usable profiles for these products, and also estimate how much additional demand – and therefore protection – would be gained from adding contraceptive or STI-protective attributes.

We also elicited the stated preferences of female sex workers for client risk, condom use, and payments for sex. Sex workers can earn more for risky unprotected sex, and we used a repeated DCE to predict risk compensation (i.e. how much condom use would change) if they were to use HIV prevention products.

What did you find most influenced people’s preferences in your research?

Unsurprisingly for products, HIV protection was most important to people, followed by STI and then pregnancy protection. But digging below these averages with a latent class analysis, we found some interesting variation within female respondents: over a third were not concerned with HIV protection at all, instead strongly caring about pregnancy and STI protection. Worryingly, these were more likely to be respondents from high-incidence adolescent and sex worker groups. The remainder of the sample overwhelmingly chose based on HIV protection.

In the second sex worker DCE, we found that using a new HIV prevention product made condoms become less important and price more important. We predict that the price premium for unprotected sex would reduce by two thirds, and the amount of condomless sex would double. This is an interesting labour market/economic finding, but – if true – also has real public health implications. Since economic changes mean sex workers move from multi-purpose condoms to single-purpose products which need high levels of adherence, we thought this would be interesting to model.

How did you use information about people’s preferences to inform estimates of cost-effectiveness?

In two ways. First, we used simple uptake predictions from DCEs to parameterise an HIV transmission model, allowing for condom substitution uptake to vary by condom users and non-users (it was double in the latter). We were also able to model the potential uptake of multipurpose products which don’t exist yet – e.g. a pill protecting from HIV and pregnancy. We predict that this combination, in particular, would double uptake among high-risk young women.

Second, we predicted risk compensation among sex workers who chose new products instead of condoms. We were also able to calculate the price elasticity of supply of unprotected sex, which we built into a dynamic transmission model as a determinant of behaviour.

Can discrete choice experiments accurately predict the kinds of behaviours that you were looking at?

To be honest, when I started the PhD I was really sceptical – and I still am to an extent. But two things make me think DCEs can be useful in predicting behaviours.

First is the data. We published a meta-analysis of how well DCEs predict real-world health choices at an individual level. We only found six studies with individual-level data, but these showed DCEs predict with an 88% sensitivity but just a 34% specificity. If a DCE says you’ll do something, you more than likely will – which is important for modelling heterogeneity in uptake. We desperately need more studies following up DCE participants making real-world choices.

Second is the lack of alternative inputs. Where products are new and potential users are inexperienced, modellers pick an uptake number/range and hope for the best. Where we don’t know efficacy, we may assume that uptake and efficacy are linearly related – but they may not be (e.g. if proportionately more people use a 95% effective product than a 45% effective one). Instead, we might assume uptake and efficacy are independent, but that might sound even less realistic. I think that DCEs can tell us something about these behaviours that are useful for the parameters and structures of models, even if they are not perfect predictors.

Your tread the waters of infectious disease modelling in your research – was the incorporation of economic factors a challenge?

It was pretty tricky, though not as challenging as building the simple dynamic transmission model as a first exposure to R. In general, behaviours are pretty crudely modelled in transmission models, largely due to assumptions like random mixing and other population-level dynamics. We made a simple mechanistic model of sex work based on the supply elasticities estimated in the DCE, and ran a few scenarios, each time estimating the impact of prevention products. We simulated the price of unprotected sex falling and quantity rising as above, but also overlaid a few behavioural rules (e.g. Camerer’s constant income hypothesis) to simulate behavioural responses to a fall in overall income. Finally, we thought about competition between product users and non-users, and how much the latter may be affected by the market behaviours of the former. Look out for the paper at Bristol HESG!

How would you like to see research build on your work to improve HIV prevention?

I did a public engagement event last year based on one statistic: if you are a 16-year old girl living in Durban, you have an 80% lifetime risk of acquiring HIV. I find it unbelievable that, in 2018, when millions have been spent on HIV prevention and we have a range of interventions that can prevent HIV, incidence among some groups is still so dramatically and persistently high.

I think research has a really important role in understanding how people want to protect themselves from HIV, STIs, and pregnancy. In addition to highlighting the populations where interventions will be most cost-effective, we show that variation in preferences drives impact. I hope we can keep banging the drum to make attractive and effective options available to those at high risk.

IVF and the evaluation of policies that don’t affect particular persons

Over at the CLAHRC West Midlands blog, Richard Lilford (my boss, I should hasten to add!) writes about the difficulties with the economic evaluation of IVF. The post notes that there are a number of issues that “are not generally considered in the standard canon for health economic assessment” including the problems with measuring benefits, choosing an appropriate discount rate, indirect beneficiaries, and valuing the life of the as yet unborn child. Au contraire! These issues are the very bread and butter of health economics and economic evaluation research. But I would concede that their impact on estimates of cost-effectiveness are not nearly well enough integrated into standard assessments.

We’ve covered the issue of choosing a social discount rate on this blog before with regards to treatments with inter-generational effects. I want instead to consider the last point about how we should, in the most normative of senses, consider the life of the child born as a result of IVF.

It puts me in mind of the work of the late, great Derek Parfit. He could be said to have single-handedly developed the field of ethics about future people. He identified a number of ethical problems that still often don’t have satisfactory answers. Decisions like funding IVF have an impact on the very existence of persons. But these decisions do not affect the well-being or rights of any particular persons, rather, as Parfit terms them, general persons. Few would deny that we have moral obligations not to cause material harm to future generations. Most would reject the narrow view that the only relevant outcomes are those that affect actual, particular persons, the narrow person-centred view. For example, in considering the problem of global warming, we do not reject its consequences on future generations as being irrelevant. But there remains the question about how we morally treat these general, future persons. Parfit calls this the non-identity problem and it applies neatly to the issue of IVF.

To illustrate the problem of IVF consider the choice:

If we choose A Adam and Barbara will not have children Charles will not exist
If we choose B Adam and Barbara will have a child Charles will live to 70

If we ignore evidence that suggests quality of life actually declines after one has children, we will assume that Adam and Barbara having children will in fact raise their quality of life since they are fulfilling their preferences. It would then seem to be clear that the fact of Charles existing and living a healthy life would be better than him not existing at all and the net benefit of Choice B is greater. But then consider the next choice:

If we choose A Adam and Barbara will not have children Charles will not exist Dianne will not exist
If we choose B Adam and Barbara will have a child Charles will live to 70 Dianne will not exist
If we choose C Adam and Barbara will have children Charles will live to 40 Dianne will live to 40

Now, Choice C would still seem to be preferable to Choice B if all life years have the same quality of life. But we could continue adding children with shorter and shorter life expectancies until we have a large population that lives a very short life, which is certainly not a morally superior position. This is a version of Parfit’s repugnant conclusion, in which general utilitarian principles leads us to prefer a situation with a very large, very low quality of life population to a smaller, better off one. No satisfying solution has yet been proposed. For IVF this might imply increasing the probability of multiple births!

We can also consider the “opposite” of IVF, contraception. In providing contraception we are superficially choosing Choice A above, which by the same utilitarian reasoning would be a worse situation than one in which those children are born. However, contraception is often used to be able to delay fertility decisions, so the choice actually becomes between a child being born earlier and living a worse life than a child being born later in better circumstances. So for a couple, things would go worse for the general person who is their first child, if things are worse for the particular person who is actually their first child. So it clearly matters how we frame the question as well.

We have a choice about how to weigh up the different situations if we reject the ‘narrow person-centred view’. On a no difference view, the effects on general and particular persons are weighted the same. On a two-tier view, the effects on general persons only matter a fraction of those on particular persons. For IVF this relates to how we weight Charles’s (and Diane’s) life in an evaluation. But current practice is ambiguous about how we weigh up these lives, and if we have a ‘two-tier view’, how we weight the lives of general persons.

From an economic perspective, we often consider that the values we place on benefits resulting from decisions as being determined by societal preferences. Generally, we ignore the fact that for many treatments the actual beneficiaries do not yet exist, which would suggest a ‘no difference view’. For example, when assessing the benefits of providing a treatment for childhood leukaemia, we don’t value the benefits to those particular children who have the disease differently to those general persons who may have the disease in the future. Perhaps we do not consider this since the provision of the treatment does not cause a difference in who will exist in the future. But equally when assessing the effects of interventions that may cause, in a counterfactual sense, changes in fertility decisions and the existence of persons, like social welfare payments or a lifesaving treatment for a woman of childbearing age, we do not think about the effects on the general persons that may be a child of that person or household. This would then suggest a ‘narrow person-centred view’.

There is clearly some inconsistency in how we treat general persons. For IVF evaluations, in particular, many avoid this question altogether and just estimate the cost per successful pregnancy, leaving the weighing up of benefits to later decision makers. While the arguments clearly don’t point to a particular conclusion, my tentative conclusion would be a ‘no difference view’. At any rate, it is an open question. In my rare lectures, I often remark that we spend a lot more time on empirical questions than questions of normative economics. This example shows how this can result in inconsistencies in how we choose to analyse and report our findings.



Sam Watson’s journal round-up for 26th March 2016

Every Monday our authors provide a round-up of some of the most recently published peer reviewed articles from the field. We don’t cover everything, or even what’s most important – just a few papers that have interested the author. Visit our Resources page for links to more journals or follow the HealthEconBot. If you’d like to write one of our weekly journal round-ups, get in touch.

Affordability and availability of off-patent drugs in the United States—the case for importing from abroad: observational study. BMJ [PubMedPublished 19th March 2018

Martin Shkreli has been frequently called “the most hated man in America“. Aside from defrauding investors and being the envied owner of a one-of-a-kind Wu-Tang Clan album, the company of which he was chief executive, Turing Pharmaceuticals, purchased the sole US approved manufacturer of a toxoplasmosis treatment, pyrimethamine, and hiked its price from $13 to $750 per tablet. Price gouging is nothing new in the pharmaceutical sector. An episode of the recent Netflix documentary series Dirty Money covers the story of Valeant Pharmaceuticals whose entire business was structured around the purchase of drug companies, laying off any research staff, and then hiking the price as high as the market could bear (even if this included running their own pharmacies to buy products at these inflated prices). The structure of the US drug market often allows the formation of monopolies on off-patent, or generic, medication, since the process for regulatory approval for a new manufacturer can be long and expensive. There have been proposals though that this could be ameliorated by allowing manufacturers approved by other trusted agencies (such as the European Medicines Agencies) to sell generics in the US while the FDA approvals process takes place. The aim of this paper is to determine how many more manufacturers this would allow into the US drugs market. The authors identify all the off-patent drugs that have been approved by the FDA since 1939 and all the manufacturers of those drugs that were approved by the FDA and by other trusted agencies. No analysis is given of how this might affect drug prices, though there is a pretty obvious correlation between the number of manufacturers and drug prices shown elsewhere. The results show that the proposed policy would increase the number of manufacturers for a sizeable proportion of generics: for example, 39% of generic medications could reach four or more manufacturers when including those approved by non-FDA bodies.

Why internists might want single-payer health care. Annals of Internal Medicine [PubMedPublished 20th March 2018

The US healthcare system has long been an object of fascination for many health economists. It spends far more than any other nation on healthcare (approximately $9,000 per capita compared to, say, $4,000 for the UK) and yet population health ranks alongside middle-income countries like Cuba and Ecuador. Garber and Skinner wondered whether it was uniquely inefficient and identified or questioned a number of issues that may or may not explain the efficiency or lack thereof. One of these was the administrative burden of multiple insurance companies, which evidence suggests does not actually account for much of the total expenditure on health care. However, Garber and Skinner say this does not take into account time spent by clinical and non-clinical staff on administration within hospitals. In this opinion piece, Paul Sorum argues that internists should support a move to a single-payer system in the US. One of his four points is the administrative burden of dealing with insurance companies, which he cites as an astonishing 61 hours per week per physician (presumably spread across a number of staff). Certainly, this seems to be a key issue. But Sorum’s other three points don’t necessarily support a single-payer system. He also argues that the insurance system is leading to increasing deductibles and co-payments placed on patients, limiting access to medications, as drug prices rise. Indeed, Garber and Skinner note also that high deductibles limit the use of highly cost-effective measures and actually have the opposite effect of reducing productive efficiency. A single payer system per se would not solve this, it would need significant subsidies and regulation as well, and as our previous paper shows, other measures can be used to bring down drug prices. Sorum also argues that the US insurance system places an unnecessary burden from quality measures and assessment as well as electronic medical records used to collect information for billing purposes. But these issues of quality and electronic medical records have been discussed in the context of many health care systems, not least the NHS, as the political and regulatory framework still requires this. So a single-payer system is not a solution here. A key difference between the US and elsewhere that Garber and Skinner identify is that the US permits much more heterogeneity in access to and use of health care (e.g. overuse by the wealthy and underuse by the poor). Significant political barriers stand in the way of a single payer system, and since other means can be used to achieve universal coverage, such as the provisions in the Affordable Care Act, maybe internists would be better directing their energy at more achievable goals.

Social ties in academia: a friend is a treasure. Review of Economics and Statistics [RePEcPublished 2nd March 2018

If you ever wondered whether the reason you didn’t get published in that top economics journal was that you didn’t know the right people, you may well be right! This article examines the social ties between authors and editors of the top four economics journals. Almost half of the papers published in these journals had at least one author with a connection to an editor, either through working in the same department, co-authoring a paper, or PhD supervision. The QJE appears to be the worst offender with (if I’ve read this correctly) all authors between 2000 and 2006 getting their PhD in either Harvard or MIT. So don’t bother trying to get published there! This article also shows that you’re more likely to get a paper into the journals when your former PhD supervisor is editing it. Given how much sway a paper published in these journals has on the future careers of young economists, it is disheartening to see the extent of nepotism in the publication process. Of course, one may argue that it just so happens that those that work at the top journals associate most frequently with those who write the best papers. But given even a little understanding of human nature, one would be inclined to discount this explanation. We have all previously asked ourselves, especially when writing a journal round-up, how this or that paper got into a particularly highly regarded journal, now we know…