Today’s “More or Less” covers fantasy takeover valuations (featuring my colleague John Gapper, for real this time), immigration and crime, music and maths, and whether the official inflation figures are a fudge.

4.30pm BST, Radio 4 - or thereafter streaming from the website.

Which nation produces the richest people in the world? You might think that an easy question to answer: just grab the latest figures from the International Monetary Fund, and you’ll see that the answer is Luxembourg ($102,000 gross domestic product per head in 2007). The US is in ninth place ($46,000) and the UK in 11th ($45,000).

There are some methodological wrinkles to iron out: what exchange rate to use, for instance. And for the poorest countries such as Liberia ($200 per person in 2007) or Burundi ($130), the numbers involve some guesswork. But overall, these are not controversial statistics – unless you are Lant Pritchett or Michael Clemens.

Pritchett, of Harvard’s Kennedy School, and Clemens, of the Washington, DC, think-tank the Center for Global Development, argue that my opening question should be answered in a radically different way. Rather than measuring the income of people who are now residents of Liberia, Clemens and Pritchett have produced a research paper estimating the income earned by people who were born in, say, Liberia, regardless of where they now live – what Clemens and Pritchett call “income per natural” of Liberians.

The remainder of this column can be read here. Please post comments below.

Dear Economist,
I have fallen in love with a wonderful man, and on Valentine’s Day he proposed to me. We’re planning to marry next summer. The question is: should we live together over the next year, or wait until we’re married? The financial impact is relatively small either way, and I am not afraid of scandal. I am just trying to work out whether some time living together is likely to make our marriage stronger or not.
Elspeth
Boston MA

Dear Elspeth,

For many years, theory pointed in one direction and evidence in the other. The theory – going back to Nobel laureate Gary Becker’s work in the 1970s – is that a period of cohabitation lets you learn more about one another and thus avoid a bad match. Your man may be charming on a date, but if he leaves his underpants lying around or eats toast over the sink to save washing up, forget it.

The overwhelming evidence, on the other hand, used to be that marriages preceded by cohabitation were more likely to break down – in the US, at least. The question is whether this was a causal relationship, or whether the cohabitation and the marital breakdown were caused by a third factor, such as social class or a lack of religious belief.

Fortunately, new empirical research from economist Steffen Reinhold suggests both that the relationship between cohabitation and divorce is not causal, and also that it has faded over time as more educated, middle-class couples choose to live together before marriage.

I recommend following Becker’s theory: learn about the marriage before it is too late by moving in together now. Keep an eye out for discarded underpants.

Questions to economist@ft.com

I read too many American blogs. They use words such as “smackdown”. Anyway, the debate between me and Dan “Predictably Irrational” Ariely continues - the collected posts are being gathered here.

In my reply to Dan’s first post, I finish by challenging him:

The weaknesses of laboratory experiments are not always quite so evident, especially when they are described as compellingly as in Predictably Irrational. So, let me point them out. While laboratory experiments are great for creating controlled conditions, they also create artificial conditions. There are several examples of important clashes between what happens in the laboratory and what happens outside. We know, for example, that procurement managers systematically screw up when bidding in a laboratory auction, but they do much better job in the (apparently identical) real life auctions situations they face everyday.
The economist John List has tried to replicate some famous “predictably irrational” results from the laboratory; the results tend to evaporate in more realistic settings. In one example I describe in The Logic of Life, List shows that the “irrational” result (which is that people given an unexpected raise work much harder than they could get away with) only lasts for ninety minutes. A gratitude effect that lasts ninety minutes is not the basis on which to rewrite your company’s human resources policy.
I’m not aware that any of Dan’s experiments have been challenged in this way, and I was pleased to see that he often tried to carry out his work in realistic settings such as restaurants and bars. So this isn’t an attack on his work–it’s more of a question. Dan, how can we be confident that these experimental results hold up in real life? And what further work would you like to see, to make us more confident in them?

Dan’s reply will be excellent, I am sure, and is due on Monday.

The Centre for Economic Policy Research reports that:

Soap operas (novelas) are watched by the vast majority of the population in Brazil, and often portray families that are much smaller that the reality for the country. The authors of CEPR DP6785 use this to examine the effects of television, and of role models portrayed in these novelas, on individual behaviour, specifically fertility choices.

Rede Globo has a virtual monopoly on the production of novelas, and an analysis of differences in the timings of Globo’s entry into areas of the country, coupled with census data, reveals that areas reached by the Globo signal had significantly lower fertility than comparable areas not reached by Globo. The magnitude of the effect is about one tenth of the effect of being married on fertility, and is comparable to that associated with an increase of 1 doctor or nurse per 1,000 people.

The authors find that the effect is strongest for women of lower socioeconomic status, and (a) is insignificant for women aged 15-24; (b) leads to an 8% decrease in the mean probability of giving birth for women aged 25-34; and (c) leads to an 11% decrease in the mean probability for women aged 35-44.

Further evidence from naming patterns and the impact of the introduction of foreign soap operas that are not seen as realistic portraits of Brazilian life indicates that it is novelas, not just televisions per se, that are behind the results.

Question - is this good news or bad news? Steve Landsburg would say bad news.

I’ll be debating with Dan Ariely (author of Predictably Irrational) on Amazon’s Omnivoracious blog. After all, our books do seem to contradict each other. Sadly, we’re both far too nice to tear strips off each other, but I suspect there will be a few disagreements…Dan’s first post is here; the Omnivoracious introduction is here. My first reply will be going up tomorrow, or perhaps Friday. And in case you were wondering, the photograph didn’t come from me: perhaps Dan was overly impressed by tales of my economics-based exercise regime.

At the Royal Economic Society conference a couple of weeks back, I sat in on an interesting overview of the Mirrlees Review of taxation in the UK. Time constraints - and fire alarms - stood in the way of a detail discussion, but lots of early position papers are up here, and I am told that the latest drafts are to follow very shortly. Here is the original Meade Review.

I have stumbled upon Raghuram Rajan’s semi-popular writings from IMF mag “Finance and Development”. Ragu, co-author of “Saving Capitalism from the Capitalists” and former Chief Economist of the IMF, is a hugely impressive thinker. These articles, neither heavy peer-reviewed stuff nor fluffy newspaper journalism, are well worth a browse. (This is the one in which Ragu not only all-but forecasts the credit crunch, but also explains the mechanisms involved, back in 2005.)

Today’s “More or Less” asks whether it matters who your child goes to school with, and explores the mathematical legacy of Gary Gygax with Michael Gove MP and Ian Livingstone of “Fighting Fantasy” fame. 4.30pm BST, Radio 4 - or thereafter streaming from the website. Photo: Scogle.

My family’s experience of the local hospital has been mixed. Sometimes it is impressive; at others it falls below the standard one would expect in the capital of a developed country. Our rule of thumb is that it’s much safer to get sick in Cumbria, where my wife’s parents live.

Although we have had our fair share of dashes to Accident and Emergency, they have been not been so frequent as to constitute a statistically rigorous study of the local facilities. Still, such studies do exist, and one recently published investigation suggests that patients in London have indeed been suffering unduly.

The reason is that many skilled workers in London have decided they have better things to do than work for the National Health Service: in the private sector they can expect to earn 50 or 60 per cent more in London than further north; in the NHS, wages for London staff are relatively meagre. As a result, hospitals in booming areas such as London have more staff vacancies, seem to over-promote staff as a way of giving them more competitive pay, and use more temporary staff hired through private agencies.

The remainder of this column can be read here. Please post comments below.