Ceteris Non Paribus

Ceteris Non Paribus is my personal blog, formerly hosted at nonparibus.wordpress.com and now found here. This blog is a place for me to put the ideas I have, and the stuff I come across, that I’ve managed to convince myself other people would be interested in seeing. See the About page for more on the reasons why I maintain a blog and the origin of the blog’s name.

My most recent posts can be found below, and a list of my most popular posts (based on recent views) is on the right.

Ceteris Non Paribus

One in five

HIV may be harder to measure than anything else we study in public health and social science. It is largely invisible to the naked eye, its transmission is low-probability and highly variable, and perhaps most importantly, people have strong incentives to hide their status and avoid testing. These incentives arise from everything from stigma to a desire to maintain access to sex partners to a perception that HIV testing is just a death sentence, with tests highly likely to be positive and bringing no benefits. We’ve gotten a lot better at measuring things like the prevalence of the virus, but even now our estimates have to be taken with a grain of salt.

Despite all that, we do have a decent sense of how common it is in different regions of the world. In urban Malawi, which includes the place I’m currently sitting, the answer is that a little over 20% of the population has the virus. For historical reasons, those rates are typically computed for the population aged 15-49, so the overall rate might differ, but that’s still a decent range for prime-aged adults (and indeed there’s no reason to think the prevalence drops drastically above that age range). HIV takes around ten years to lead to death, with visible AIDS lasting for something like one year. So as a basic estimate, 20% of people are carrying the virus, but just 2% would be visibly ill. That second number is small enough to ignore, so about one out of every five people in Lilongwe is infected with HIV.

This is a nearly-incomprehensible figure for me. Sometimes if I pass through crowds I try to imagine that every fifth person I pass has an incurable virus (although many don’t know it). I honestly can’t do it – they all look like regular people to me, because that is exactly what they are. But all the evidence I’ve seen indicates that people here do manage to wrap their minds around the idea that one in every five people in the street (or one in every five potential sex partners, or one in every five people on their soccer team) is infected with HIV. I have no idea how they manage it, either psychologically or in terms of making important life decisions about stuff like whom to marry. People often wonder what an economist is doing studying HIV prevention. The answer is that the choices people make about sex and marriage in the face of HIV constitute what I would argue is the hardest – and the most interesting – decisionmaking problem in the world.

High dispersion in inflation rates

Last night I met a former hotel employee who hand-calculated inflation figures for the region around his resort, using year-on-year price changes for the official consumer price basket. He came up with an annual inflation rate (if memory serves) of 28%, which is nearly two and a half times the official Reserve Bank of Malawi figure of 11.4% (as of March).

I’m really surprised that the local rate would be so much higher than the national one, since a lot of the goods in the basket are fairly tradeable. I don’t, however, suspect that things are being intentionally gamed: I know lots of folks who currently or formerly worked at central banks and even interned at one myself, way back when, and they’re uniformly well-intentioned data geeks like myself. But this is a way bigger spread than we see, for example, across US regions, so I’m at a loss to explain what’s going on.

Out with the new

I spotted this sign of renewal on my way out of Kamuzu International Airport:

That’s the original Malawi flag, featuring a red, rising sun. The late President Bingu wa Mutharika changed it to a new version with a white sun in the middle in 2010, in a widely unpopular move that allegedly cost on the order of twenty million dollars.

The BBC reports that the Malawi parliament voted to change the flag back to the red-sun original in late May of this year, but that the new President, Joyce Banda, still had to sign the bill into law. I can’t find any confirmation online that she actually did so, which is a pattern common to many news stories in Malawi – there’s often just an initial report, and no followup. But I’ve seen it with my own eyes, which is good enough.

As an added bonus, I’ve heard that the change back won’t be nearly as expensive: all they have to do is take the pre-2010 flags back out of storage.

Why I'm back

This post marks my triumphant return to the blogosphere after a too-long hiatus from writing over at MethodLogical. Why? In short, I’ve found myself wanting my own independent forum to store my thoughts and throw up links to cool stuff and pictures of what I’m up to. This is all detailed in the about page, which I will quote wholesale because no one can stop me:

  This blog is a place for me to put the ideas I have, and the stuff I come across, that I’ve managed to convince myself other people would be interested in seeing. It also serves as a way for folks who care what I’m doing (hi, mom!) to keep track of what I’m up to when I’m on another continent or otherwise out of touch. I’ve done stuff like this in the past, but my previous blogs have been trip-specific (Jason Does India) or joint efforts with other people (Positive Impact Institute, Methodlogical). This time, it’s a solo effort, and one I intend to last. That means that I am aiming a bit lower – at one-off opinions without tons of research or effort, rather than the kind of thorough, thoughtful analysis that the bloggers at Development Impact put up each week. In this I am inspired by Chris Blattman’s thoughts on staying power and blogs. He was probably being facetious when he said that “sometimes I even read part of the papers I reference”, but in my posts here I may do that quite literally. Carefully thinking things through what my day job is for (sort of – I’m a graduate student, but the point still stands); this blog is intended for stuff that’s just a bit too highbrow for facebook. “Ceteris Paribus” is Latin for “other things equal”, and is the implicit assumption in all causal analyses. Suppose I observe groups A and B, seeing that group A does X while B does not, and therefore deduce that the different outcomes in A are attributable to X. This is true so long as ceteris paribus holds – if X is the only difference between the groups. Scientists can use randomized experiments to ensure that all else is in fact equal, but in the absence of an experiment it is almost always the case that ceteris non paribus: tons of other stuff is going on. I’ve named my blog after my obsession with this basic inferential error, because, while people make it everywhere, my research areas (public health and development economics) are especially plagued by failures to hold all else equal. Articles on Yahoo! News treat people who don’t drink red wine as a valid comparison group for people who do, and find all kinds of spurious health benefits. NGOs and advocates select the best schools located closest to roads for a pilot intervention, then tout the big advantage in test scores between the intervention schools and the rest of the country. 90% of my academic work boils down to saying “not so fast – what’s your comparison group?”, and one major purpose of this blog is for me to vent my frustrations about people constantly getting it wrong.

Who am I? If you’re reading this then you probably already know me, but you can still check out one of those false-third-person biographies here.