Mom and Dad . . . double chins cascading onto their burgerbellies . . . are armed for shopping.

Welcome to the fat and conservative suburbia that our intellectual urbanites loathe for its alleged propensity to burn petrol, disregard for food labels and their conservative family values. To some, our suburbs are what a first circle of Hell would look like were it populated by the ordinary folks.

But how are suburban sprawl and rising obesity . . .and the my-family-is-myfortress philosophy . . . actually related?

The latest figures from the CSO and several surveys suggest that suburban sprawl . . .

increasing share of population living outside compact city centre areas . . . has been positively correlated with higher obesity levels. Furthermore, most of the studies identify suburban locations as the areas with lower rates of divorce and longer duration of marriages than the urban locations.

The real problem with these figures is that as any economics undergraduate knows, correlation does not imply causation. In other words, an observation that more obese and family-centred people live outside the city centre does not mean that suburban existence causes obesity or that moving people into the city makes their values less conservative.

In a paper titled 'Fat City', researchers at the University of Toronto, London School of Economics and Universitat Pompeu Fabra (Barcelona) looked at the relationship between suburbia and obesity.

Using data tracking 6,000 Americans since 1979, the study finds "no evidence that urban sprawl causes obesity". Instead, "previous findings of a positive relationship most likely reflect a failure to properly control for the fact the individuals who are more likely to be obese choose to live in more sprawling neighbourhoods." These results hold for both men and women.

In other words, a person who drives instead of walks is more likely both to be overweight and to live outside the city. Simply forcing such a person to live in a higher density neigbourhood, as often suggested by our public health gurus, will not cause any change in their health.

Another paper published in February this year, titled 'Sin City?' looks at the question of whether couples moving out of the city to more remote areas really signal stronger marriage commitment. Using the data from Denmark, researchers look into the marriage and cohabitation patterns of some 20,000 individuals observed over the period of fifteen years. The authors find "that of the couples who married in the city, the ones who stay in the city have significantly higher divorce rates. Similarly, for the couples who married outside the city, the ones who move to the city are more likely to divorce."

People in more stable marriages are arguably more likely to want kids and to buy a house. Since kids require more space we should find a large proportion of the stable marriages outside the city.

Suburban living also means spending a larger fraction of time together and this requires a stable relationship.

So living outside the city may be preferential for more stable couples.

On the other side of the argument, the rate at which singles meet potential partners is higher in the city.

Therefore, singles will move to the city to exploit this advantage. The same observation suggests that leaving the city can be used as a credible commitment device for couples to stabilise their relationship. These are the causal arguments that tie life outside the city to higher rates of marriage success.

To the chagrin of those who would argue that living in the suburbs causes people to become more conservative, the data analysed in 'Sin City' shows no such relationship.

Instead, just as with obesity, people with more stable familial relationships tend to prefer suburban living as it offers them a wider range of choices in housing, schooling and quality-of-life amenities they care about.

The suburbs may be fat and the cities may be sinminded, but giving the suburbanites better public transport or raising housing density in their areas . . . just a few things proposed to remedy suburban sprawl . . . is unlikely to change the suburbanites.

Yet the real question remains unanswered: since obesity is positively correlated with marriage longevity, is higher body mass causing people to stay married longer or is staying married longer causing people to grow more obese?

Dr Constantin Gurdgiev is an economist and editor of Business & Finance magazine