jamesz

How do habits help?

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We’ve posted over the past couple of days about habit persistence and you might be wondering why anyone would care. It turns out that habit persistence is extremely powerful in explaining some important macroeconomic dynamics:

When habits are formed at the level of individual goods, firms take into account the fact that the demand they will face in the future depends on their current sales. This is because higher consumption of a particular good in the current period makes consumers, all other things equal, more willing to buy that good in the future through the force of habit. Thus, when habits are deeply rooted, the optimal pricing problem of the firm becomes dynamic.

[This paper embeds] the deep-habit-formation assumption in an economy with imperfectly competitive product markets. This combination results in a model of endogenous, time-varying markups of prices over marginal cost [with] markups [that] behave counter-cyclically. In particular, expansions in output driven by demand shocks are accompanied by declines in markups. This implication …is in line with the existing empirical literature. In addition, …because of the strong counter-cyclical movements of markups, [habit persistence] is capable of explaining increases in wages and consumption in response to a positive demand shock as is observed in the data. This latter empirical regularity has proved difficult to explain with standard models of the transmission of demand shocks.

jamesz

Why do people form habits?

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Matt stormed back on to the blog yesterday with a post on the importance of habits in explaining human behaviour. Here I want to explore the way in which economists describe habits in a bit more depth. In particular, Matt asked why economists talk about habit persistence in such an ad hoc way. I don’t think it’s very ad hoc at all and I’ll try to explain why.

What are habits?

Having a habit means that you’re more likely to do something the more you’ve done it in the past. You’ve done it before, so that makes you more likely to do it now. The implication is that your current payoff from the activity depends upon how much you’ve done it in the past. The ‘how much you’ve done it in the past’ is what Matt refers to as ‘capital’, in the vein of Becker and Murphy’s seminal discussion of cigarettes.

How do economists describe habits?

Now the description in economic models is fairly obvious: your ‘utility’ depends not just on how much of something you get today, but also how much you got in the past. The easiest way to model that is to take the difference of today’s consumption and yesterday’s. That way, you want to consume more of something than you did yesterday, and consuming less than yesterday will make you less happy. Essentially, yesterday’s consumption can be thought of as the stock of ‘capital’ that Matt referred to. The more capital you’ve built up over time, the more you want to do the thing again today. Hence, with this simple mechanism, we get habit formation and persistence.

What I’ve just described is called ‘internal’ habit persistence because it depends on your personal consumption levels. However, it is easily generalised to societal habits by taking the stock of built up consumption to be average social consumption, or the consumption of one’s neighbours. Then we call it ‘external’ habit persistence.

Why do they do it that way?

So far so good, but the question Matt asked is why it’s modelled that way. As he pointed out, it’s not enough just to say it fits the observed behaviour: we also have to ask why. Now that we’ve got this far it’s actually fairly straightforward. Habit persistence is simply the dependence of your personal payoff on a reference level of consumption, as opposed to being dependent on the level of consumption.

Economists have studied reference dependence ever since the canonical work of Kahneman and Tversky on prospect theory back in 1979. They drew on the psychological evidence to show that people care not about the level of consumption but the change in consumption relative to some reference point. Now, there is a lot of discussion about what an appropriate reference point is. Depending on what the reference point is you can get very different behaviours, and there can hardly be a dozen different reference points (although some weighting across them may be plausible).

The main point for our discussion is that viewing habit persistence as the result of reference-dependent utility allows us to sheet it back to some empirical literature on psychology and behaviour.

Matt Nolan

Habit formation and the economic core

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I have repeatedly been informed that the “economic man” is a poor description of individuals, and given this economic models provide a poor description of the world we live in.  As I have said previously, I don’t agree with this conclusion – and we really need to ask what an economic model is, and why we are using it, to understand the scope of economics and the appropriateness of the assumptions.

In essence my view is that we use economic models to describe, and in some way explain, tendencies that exist (from induction) using assumptions about choice that satisfy two conditions:

  1. They are as weak and loosely binding as possible
  2. They are appealing in the sense that, when I ask myself about my actions I can deduce laws that guide them.  I could go a step further and say that we can set up “ideal experiments” in our minds, but I’ll leave that for now.

This is all well and good.  But then someone will say “what about habit formation“.  This is an important issue, people obviously develop habits and these habits bind and constrain behaviour.

In fact, I would go as far as to say that habits, and the formation of habits, provide the key to tying together a lot of different strands in experiments and behavioural economics – and that an understanding of habits and habit formation is an important part of improving economists way to describe the world and give advice.

So how do we “describe habits”?

Read more

jamesz

Why do Nigerian scammers admit they are from Nigeria?

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Abstract:

False positives cause many promising detection technologies to be unworkable in practice. Attackers, we show, face this problem too. In deciding who to attack true positives are targets successfully attacked, while false positives are those that are attacked but yield nothing. This allows us to view the attacker’s problem as a binary classification. The most profitable strategy requires accurately distinguishing viable from non-viable users, and balancing the relative costs of true and false positives. We show that as victim density decreases the fraction of viable users than can be profitably attacked drops dramatically. For example, a 10x reduction in density can produce a 1000 reduction in the number of victims found. At very low victim densities the at- tacker faces a seemingly intractable Catch-22: unless he can distinguish viable from non-viable users with great accuracy the attacker cannot find enough victims to be profitable. However, only by finding large numbers of victims can he learn how to accurately distinguish the two. Finally, this approach suggests an answer to the ques- tion in the title. Far-fetched tales of West African riches strike most as comical. Our analysis suggests that is an advantage to the attacker, not a disadvantage. Since his attack has a low density of victims the Nigerian scammer has an over-riding need to reduce false positives. By sending an email that repels all but the most gullible the scammer gets the most promising marks to self-select, and tilts the true to false positive ratio in his favor.