Discounting Ethics in Macroeconomics

For macroeconomists (and perhaps philosophers)

In the Ramsey model (aka the representative agent model, the infinite life model, or what Romer calls the Ramsey-Cass-Koopmans model), agents care about their children’s utility as if it was their own. However, because they are impatient, they discount their children’s utility as they do their own. They therefore act as if they live forever. When teaching this [1] we say that the decentralized equilibrium is identical to the allocation that would be chosen by a benevolent social planner, who maximizes the utility of the representative agent.

When we teach the OLG model, we normally describe this model as involving agents who do not care about their children.[2] We note that the decentralized equilibrium would only be equal to the optimal allocation by chance. This is often done by showing that it differs from the golden rule allocation (the allocation that maximises steady state consumption), but some texts (e.g. Blanchard and Fischer) note that it would also differ from an allocation where the social planner showed some impatience over the utility of the unborn. In either case it is assumed that a benevolent social planner would put some value on the utility of the unborn.

It strikes me that the treatment of the two models is inconsistent. The claim about the Ramsey allocation involves an ethical assumption, which is that we allow the current generation to value the utility of the unborn. The benevolent social planner takes that valuation. Putting it another way, the benevolent social planner only maximizes the utility of the current generation, and makes no independent judgment about the utility of the unborn. Textbooks do not usually put it that way, but it seems to me this has to be what is being assumed.[3]

If we applied the same ethical judgment in the OLG model, where agents were entirely selfish, then the benevolent social planner should aim for an allocation which attempted to exploit the unborn as much as possible for the benefit of current generations. They should not be using a social welfare function which gives any weight to the utility of the unborn, and certainly not be thinking about the golden rule allocation. Instead, they should reflect the preferences of the living generations.

No one as far as I know tries to do this, presumably because it appears morally abhorrent. We want to overrule the selfish preferences of OLG agents. However, why is this acceptable in an OLG context, but not acceptable for agents in the Ramsey model?  If Ramsey agents had impatience (a rate of time preference) of 5% pa, then they are giving the utility of their children a weight of between 0.35 and 0.2 compared to their utility today. That is not so different from a weight of zero.

This point is clearer still if we look at the Blanchard/Yaari Model of Perpetual Youth, where agents do not care about their children but face a constant probability of death. A social planner that maximized the utility of the current living generations would discount at the same rate individuals do: impatience plus the probability of death. However I have not seen any papers that do this. Calvo and Obstfeld take a utilitarian perspective, and explicitly note that there is no necessary connection between the rate (if any) that the social planner uses to discount generations and the personal rate of time preference (with or without the probability of death). Once again, why is this distinction made in the context of this particular OLG model, but not when we look at the Ramsey set up where agents do care about their children?

It seems to me that if macroeconomists want to be consistent[4] they need to do one of two things. If they want to continue to insist that a benevolent social planner should use the personal rate of time preference of the current generation to discount future generations, then they should also make the social planner ignore the utility of the unborn in OLG models where agents are assumed not to care about future generations. They should also be transparent about the ethical assumptions they are making in the Ramsey case. (The potential double meaning in my title was deliberate). Alternatively, if they do not want to adopt this ethical position, they need to allow the rate at which the social planner discounts future generations (if any) to differ from individuals impatience in the Ramsey set-up as well as OLG models.[5] I have my own view on which is the better choice, but the point of this post is to suggest that at the moment macroeconomists are collectively just being inconsistent.

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[1] This post reflects the masters teaching I have just completed. I used to follow Romer in teaching the Ramsey model first, and then the OLG model. This year I have experimented with the reverse order (in the spirit of Obstfeld and Rogoff), which has helped highlight the issue I discuss here.

[2]This is crucial. If we described OLG as involving agents who would like to give Barro bequests but for some reason could not do, then my inconsistency argument does not apply.

[3] Future generations would only be happy with this if they gave the utility of their parents a much higher weight than their own. Somehow I do not think this is very realistic.

[4] The only grounds to be inconsistent would be that agents who give a weight to their children of zero should be treated differently than those that give it a non-zero weight. I cannot see what philosophical argument could be used to justify this, but I am not a philosopher.

[5] This is what the Stern Review on climate change does. 

Paternalism and Irrationality

I have talked before about how most economists have an instinctive dislike of paternalism: a dislike of the idea that someone (usually someone in authority) knows better what is good for people than people themselves. I think this is a very good instinct to have, but sometimes it has to be set to one side. Economists should know this, because they often use economic theory in a paternalistic fashion.

How can I write this last sentence? After all, are economists not very careful to focus on agent’s revealed preferences, rather than any objective model of what is good for people? They prefer what people actually choose as measures of well being (like consumption), rather than some scheme of what is involved in the good life dreamed up by some philosopher.  

However, as Daniel Hausman discusses in a recent book, the idea that a preference based measure of individual welfare can ever be a completely adequate measure of individual well-being is deeply problematic. There are many reasons for this, but the one most economists recognise is where individuals clearly act in ways that are not in their own self interest (or in the interest of others). The example I used before is seat belts.  But behavioural economics and experimental data are giving us many more. For example, an individual’s choice may be influenced by the presence of irrelevant alternatives: the choice between A and B may be influenced by whether C is an option, even though A and B are both preferred over C.

These features of behaviour pose an obvious problem for any preference based measure of well being. What economists typically do, faced with this dilemma, is one of two things. The first may be to deny the premise that agent’s choices in these cases are inconsistent with their own self interest. Failing that, the second response is to try and correct the preference measure of welfare to get round the problem. For example, if someone’s preference for not wearing seat belts is due to ignorance about the statistics, then we might be justified in imagining what their views would be if they did have this information. We can talk about welfare as involving maximising preferences that are not based on false beliefs. The idea is that maximising these purified preferences then maximises individual well-being.

There are a lot of problems with this approach, which Hausman discusses in detail. However, it strikes me that once this attempt is made, economists themselves tend to be paternalistic. Because how do we judge whether preferences need correcting? Often we simply ask whether choices are consistent with rational choice theory i.e. the basic axioms of much of microeconomics. If they are not, then any preferences that violate these axioms need correcting. What we are doing here is elevating rational choice theory, or more generally the micro theory we typically use, to an objective theory of well being.

Let me give one final, and rather more complex, example. There is a lot of evidence (and has been for some time e.g. Ainslie (1992), Picoeconomics, CUP.) that individuals discount over time in a hyperbolic way, rather than in the simple exponential manner which captures impatience as a constant discount factor. Hyperbolic preferences mean that if the choice is between A now and B in x periods time, we may choose A, but if it is between A in y periods time, and B in y+x periods, we choose B. Now hyperbolic preferences cause problems because they are clearly time inconsistent. From a welfare point of view, we have to ask who is the individual whose welfare we are maximising: the individual today with one set of preferences, or the individual tomorrow with different preferences. Faced with this dilemma, economists and governments typically ignore the preferences agents actually have, and carry on using a constant discount rate. Yet if this is not what people actually do, does it make sense to discount at all?    

In this and many other ways, economists appear quite happy to ‘correct’ the preferences people have, and instead make judgements on the basis of the preferences they should have. That may be the sensible thing to do, but it seems pretty paternalistic to me.