The ‘right’ level of mobility
26/01/2012 § 9 Comments
Oh dear. Tyler Cowen has suggested that class mobility might not be that bad, and John Quiggin has taken him to task. The underlying question is, what level of mobility would indicate a meritocracy? Or at least the level of meritocratic reward we prefer? Does low mobility in itself indicate lack of meritocracy?
In the last year or two, I have joined both Mensa and the Triple Nine Society. It turns out that high IQ societies are obsessed with IQ measurements and what they mean. For example, the last TNS newsletter had a great article on the Flynn effect (named for NZ’s own Prof Flynn, University of Otago). I have therefore been reading and thinking lately about what IQ is and what it profits a person.
This debate about mobility and meritocracy touches on three issues:
- selection of breeding partner
- heritability of intelligence/IQ
- correlation of earnings and IQ.
Conceptually, if people select breeding partners with similar IQs, IQ is totally inherited, and earnings correlate perfectly with IQ, then society will be both rigid and meritocratic. Relax any of the conditions, and you introduce mobility into a meritocratic society. If we then take as given:
- individuals are allowed to select their preferred partners
- individuals will prefer partners similar to themselves
- heritability is biologically determined, rather than decided by social policy,
we are left with asking, what should be the reward for a given level of IQ?
I built a small spreadsheet model to try to understand this. I generated 100 people with random IQs (mean=100, SD=15) and gave them incomes equal to exp(IQ/10). I paired them so as to minimise the sum of the squares of the differences in IQ across all breeding pairs (1000 random draws). Then, each pair had two children. Their IQs were 50% random and 50% inherited. Their incomes were also equal to exp(IQ/10).
I put both the parents and children into quintiles and calculated the class mobility of the children. Here is the result:
All the inputs to the model are subject to debate. How inheritable is IQ? How do we select mates? How much should or does income depend on IQ? What are social preferences for equality of outcomes?
The key point is that, given the right parameters, you can have both class rigidity and meritocracy.