The declining returns to higher education in Australia

In yesterday's post, I discussed a recent meta-analysis on the returns to compulsory schooling. That research was necessarily focused on secondary education. What about the returns to higher education? Two recent articles tell an interesting story about the change over time in returns to higher education in Australia.

The first article is this one by Elisa Birch and Alison Preston (both University of Western Australia), published in the journal Economic Record (open access). Using data from the Household, Income and Labour Dynamics in Australia (HILDA) survey, they document a striking decrease in the returns to higher education over the period from 2001 to 2023. They apply a fairly standard Mincer wage equation, comparing hourly earnings between workers aged 28 to 38 years with no post-secondary qualification to those with one of seven categories of education: PhD; Master’s; Graduate Diploma; Graduate Certificate; Honours; Bachelor’s; and Diploma/Certificate. Strictly speaking, these estimates are wage premiums associated with different qualifications, rather than necessarily causal estimates of the returns to obtaining those qualifications. Nevertheless, they do show some interesting trends, and their headline results are summarised in Figure 2 from the paper:

Notice that, in all cases (except, arguably, Graduate Certificates), the general trend in the returns to higher education has been downward. The wage premium between higher education and no post-secondary education is lower in 2019-2023 than it was in 2001-2005. Birch and Preston also look in more detail at the difference in returns between the early period in their data (from 2001-2011) and the later period (from 2011-2023), and the differences by gender, and find that:

...over the study period, the wage premium for a Master’s degree declined by 13.2 per cent for males. For females, the decline in the Master’s wage premium was even more pronounced, falling by 16.6 per cent... The reduction in the return to a Bachelor’s degree was similar for both males and females, with a decrease of approximately 13 per cent in both groups. In Period 2, the wage premium on a Master’s degree was equal to 35 per cent among men and 26 per cent among women (a gender gap of 9 percentage points). Among Bachelor’s degree holders the wage premium in 2012–23 was equal to 27 per cent among men and 22 per cent among women (a gender gap of 5 percentage points).

So, there isn't even anything positive to say about the changes in relation to the gender wage gap. The higher wage premium for male graduates remained the same, or increased, compared to the wage premium for female graduates. Even worse, when looking across the whole wage distribution, Birch and Preston find that:

While the male wage structure appears to have shifted downward and flattened, the female wage structure shows both a downward shift and a notable decline in returns at higher wage levels.

So, the returns to higher education have been declining in Australia (a result that other studies have also found), particularly at the upper end of the wage distribution for women. Birch and Preston largely leave open the question of why. That is where this new article by Michael Coelli and Jeff Borland (both University of Melbourne), published in the journal Australian Economic Review (open access), comes in.

Coelli and Borland first note that the decline in the returns to higher education is concentrated in the period after 2001, using five-yearly Australian Census data from 1981 to 2021, and using income as a measure (rather than hourly earnings, which isn't available in the Census). Then, they explore different explanations for why the returns to higher education changed, focusing on explanations that might explain a decrease starting around 2001. They find little support for a slowdown in skill-biased technical change relative to increases in the supply of skilled workers. Instead, they find that the decrease is associated with a relative increase in the wages of workers with no post-secondary education since 2001, and link that to two main probable causes.

First, the Federal Minimum Wage began increasing in real terms from 1996. On top of that:

The method of setting wages for employees covered by awards during 1993 to 2010 may also have raised the relative wages of low‐skill employees. During that time, the annual increases to rates of pay for employees covered by awards were made in flat dollar amounts, resulting in higher percentage growth in wages for lower wage earners. This may have underpinned stronger wage growth in low‐skill occupations... Award rate increases were above inflation at the lower end of the wage distribution (especially at the minimum wage), but below inflation further up the distribution. Since 2011, a common percentage increase has been set for employees covered by all awards.

So, the process of wages being determined by awards, alongside an increasing real minimum wage, may have compressed the wage distribution, especially before 2011. This would have the effect of raising wages for workers at the bottom of the wage distribution, including many workers without post-secondary education, relative to workers at the top of the wage distribution, including many workers with higher education.

Second, Coelli and Borland note that:

Starting around 2001, Australia experienced a large and extended boom in mining, coinciding with the rise of China in global trade after its accession to the WTO. This affected employment in mining and in construction. Its impact was felt more strongly among low‐skilled workers than among the higher‐skilled.

Since workers with no postsecondary education are more likely to be working in mining and construction than workers with higher education, the former workers likely benefited disproportionately from the mining boom.

Alongside those two explanations, Coelli and Borland also note a phenomenon that they call 'occupational downgrading':

Growth in the supply of workers with a bachelor's degree generally exceeded demand growth throughout the 1981 to 2021 period, leading to them moving down the jobs ladder.

These three explanations (minimum wages and wage awards; the mining boom; and occupational downgrading) are Coelli and Borland's explanations for the decrease in the returns to higher education. They do leave some questions from Birch and Preston unanswered though - why has the decrease in the returns to higher education been concentrated among the top of the wage distribution for female workers? The top of the wage distribution is least likely to be affected by minimum wages and wage awards. However, that leaves the other explanations for the decrease. Is it because female workers are more likely to 'occupationally downgrade'? Or, did female workers miss out on the mining boom? Clearly, there is more research to be done here.

Read more:

• Internal rates of return for college majors in the US
• The returns to each additional year of compulsory schooling

The returns to each additional year of compulsory schooling

This week, my ECONS102 class is covering the economics of education. Part of that topic considers the private education decision - the decision each individual makes about the amount of education they receive. This depends on the private costs and benefits of education. Arguably the primary benefit of education is incremental income - the additional lifetime earnings that education brings.

How big are those gains? Previous studies I have seen (such as a study reported in Paul Oyer's book Everything I Ever Needed to Know about Economics I Learned from Online Dating (which I reviewed here)) have estimated effects in the order of 10 percent per additional year of education. However, that was a single study, which could easily provide a biased view if considered in isolation.

What are the effects more generally? This recent article by Gregory Clark and Christian Nielsen (both University of Southern Denmark), published in the journal Kyklos (open access), provides an answer based on a meta-analysis of 79 causal estimates of the effect of an additional year or years of compulsory schooling on earnings, drawn from 53 other papers that apply methods consistent with causal inference. Meta-analysis provides a method of combining the estimates across many studies into one overall estimate. Importantly, Clark and Nielsen apply various methods to correct for the effects of publication bias (which is the tendency for statistically significant results to be more likely to be published, while statistically insignificant results tend to be missing from the research record).

Clark and Nielsen report baseline results that are somewhat lower than I expected:

With these procedures the average percentage gain in earnings from an additional year of schooling was 8.2% for 79 independent estimates, from 53 papers... If these estimates are weighed by their precision in a random effects estimation, the gains are reduced to 6.0%, and similarly 6.2% for a fixed effects weighting.

Given that the true effect is likely to vary across populations and study settings, I would consider the random-effects estimate of 6.0 percent for each additional year of schooling as the more plausible of the three. However, Clark and Nielsen also employ meta-regression, using PET (Precision Effect Test) and PEESE (Precision Effect Estimate with Standard Error) regression models, which are designed to address imprecision and publication bias in the overall sample of results. After removing some outliers, these approaches suggest:

...a true effect of 6.1%–6.4% to an extra year of education and an insignificant effect of publication selection...

So again, it seems like the effect may be in the order of six percent per additional year of schooling. Interestingly, Clark and Nielsen themselves note that the PET-PEESE evidence for publication bias is highly model-dependent, and that these results could instead reflect genuine heterogeneity in the true effect. However, Clark and Nielsen go a little further, looking in more detail at the distribution of effects across the 79 estimates. They note that if the estimates of the earnings return were normally distributed, then there are a lot of 'missing' studies with negative returns. They also consider whether the underlying returns might be log-normally distributed. Once you consider sampling error, the log-normal distribution can still generate negative estimates, and Clark and Nielsen argue that there are fewer negative estimates in the published literature than the model would predict. Consider Figure 10 from the paper:

In the figure, the yellow bars show a histogram of the 79 estimates in the sample. The blue line shows a log-normal distribution based on the estimates. Notice that, compared with the log-normal distribution, there are more studies than expected with estimates in the 0-4 percent range, and too few in the negative range. Clark and Nielsen argue that, if the 'missing' studies were included, a better estimate of the returns to each additional year of schooling may be in the range of 0-3 percent.

However, I’m not convinced that Clark and Nielsen’s distributional assumptions are justified here. Figure 10 (like Figure 8 in the paper) shows that the observed distribution of estimates doesn’t match their chosen distribution. But they haven’t established that their chosen distribution is what we should expect in the absence of publication bias. That distribution would depend on differences in estimation methods, the precision of the estimates, and genuine differences in returns across the populations studied. A mismatch between their chosen distribution and the observed study estimates therefore does not, by itself, demonstrate that studies with negative estimates are missing. So, while publication bias remains a possible explanation, I would treat Clark and Nielsen’s proposed 0-3 percent range for the average return very cautiously.

Nevertheless, overall it does seem clear from their other results that the returns to an additional year of schooling may be somewhat lower than the 10 percent found in other studies. What would be interesting to know next is whether the estimated returns have been changing over time (which my next blog post will look at, for Australia), and what study features lead to different estimates. Clark and Nielsen do note that instrumental variable regression leads to higher estimates than difference-in-differences or regression discontinuity estimates. However, there are other contextual variables that may matter as well. Hopefully, someone else can pick up on this work and take it to the next step. That might help to distinguish publication bias from the more mundane possibility that there simply isn't a single 'true' return to an additional year of schooling.

Read more:

• Internal rates of return for college majors in the US

The costs of traffic noise

Traffic noise is an example of a negative externality - the impact of an action on a third party (a 'bystander') who has not consented to or played any role in the carrying out of that action. In this case, traffic noise caused by drivers on the road negatively affects people who live nearby, and those people haven't played any role in creating the noise.

To the extent that traffic noise negatively affects people living nearby, it should be reflected in property prices. Under hedonic demand theory, when someone buys a property they are really buying a bundle of characteristics of the property, one of which is the presence of traffic noise. Since traffic noise is a negative characteristic, we would expect properties that are exposed to more traffic noise to have lower prices, ceteris paribus (holding all else constant).

That means that the cost of traffic noise can be evaluated by carefully looking at the relationship between property values and traffic noise. That is what this 2025 NBER Working Paper (ungated here) by Enrico Moretti (University of California, Berkeley) and Harrison Wheeler (University of Toronto), sets out to do. They start by looking at the effect of roadside noise barriers on property prices, noting that these barriers provide an exogenous source of variation in traffic noise. They compare houses that are close to the barrier (within 500 metres directly away from the barrier) with those that are further away (between 500 and 1500 metres), using a difference-in-differences (DiD) strategy. That involves comparing the change in property prices between before and after the barrier was erected, between properties close to and those further away.

Moretti and Wheeler primarily use data from Florida, which provides details about the noise barriers that were completed, but also about barriers that were proposed but not completed. That also allows them to use a 'triple-differences' strategy, by matching areas that had a barrier erected, with those that didn't (but where one was proposed). Now, it turns out that the results from the triple-differences model are similar to the more standard DiD, but that should provide some further comfort with the robustness of the DiD results. The data on house prices and other characteristics comes from CoreLogic and covers the period from 1990 to 2022 (house prices) or 2006 to 2022 (property characteristics). Their final dataset includes nearly 600,000 home sales within 1500m of a noise barrier (and on the same side of the road as the barrier).

Focusing on their results that include parcel fixed-effects (so that time-invariant property characteristics are controlled for), Moretti and Wheeler find that:

For houses within 100 m of the barrier, the estimated effect increases to 8.59%. For houses 100–200 and 200–300 m from the barrier, the estimated effects increase to 5.79% and 4.41%, respectively. The effect on properties 300–400 m from the barrier is marginally statistically significant.

So, reducing traffic noise increases property values, and the effect is largest for properties closest to the road generating the noise. Beyond about 300 metres, the effect is statistically indistinguishable from zero, but within 300 metres, the construction of a noise barrier increases property values by between 4.41 and 8.59 percent. Moretti and Wheeler then note that:

Since our data report the construction cost of each barrier, we can compute the marginal value of public funds (MVPF), defined as the property value appreciation over costs... The average MVPF for barriers that were built amounts to 1.7, while the MVPF for barriers proposed but not built is 1.4. This is to be considered as a back-of-the-envelope calculation that ignores property taxes. Property taxes would reduce both the social benefits (since some of the home value increase gets taxed), and the social costs (since property taxes end up in local government coffers).

So, on this measure at least, noise barriers appear to be a good use of public funds, since the increases in property values exceed the costs of erecting the barriers (although noting that there may be other uses of public funds with even higher MVPF values).

Next, Moretti and Wheeler change their model in order to allow the change in price to vary based on the expected decibel reduction. They use a model where the effect is non-linear in noise reduction, and find that:

The effect plateaus at 10 dB of reduction, which represents the 96th percentile in our sample. The effect is estimated to be zero when noise reductions are 4.9 dB...

The average barrier in our sample reduces noise by 7.15 decibels. At this level of noise reduction, our estimates imply that the average price of a decibel is 0.94%...

That is the result that Moretti and Wheeler use later in their paper to estimate the economic cost of the externality. However, first they need to rule out some competing explanations for their effects. They show that air quality is somewhat better near to the barriers, but the effect is small and not statistically significant. They show that the results do not change when accounting for tree canopy or the presence of other buildings, meaning that noise barriers blocking views of the road is unlikely to explain the results. And, they show that the construction of new homes (with higher unobserved quality) does not explain the results.

Moretti and Wheeler next use their results to estimate the economic cost of the externality for each census tract in the US. From that, they find that there is:

...a negative correlation between the cost of the externality and median family incomes. The slope is -0.10 (0.01), indicating that a 10% lower income is associated with a 1% higher per capita cost. The correlations with the share of residents who are Black and the poverty rate are positive. The slopes are 0.08 (0.01) and 0.63 (0.05), respectively, indicating that a 10 percentage point higher share of Blacks or a 1 percentage point higher poverty rate are associated with 0.8% and 0.6% higher per-capita costs...

That means that the externality cost is regressive. That is, the cost of the externality is a larger proportion of income for low-income families than for higher-income families (taking into account the location of low-income and higher-income families and the property values where they live and the traffic noise they face).

In total, Moretti and Wheeler estimate the cost of traffic noise to be US$7.0 billion in Florida, and $109.75 billion for the US as a whole. Looking across cities, they find that per-capita traffic noise costs increase with urban share of the population and population density, which they suggest is because cities with greater urban share or those that are denser have both higher noise exposure, and higher property values.

Finally, Moretti and Wheeler estimate that a one-off Pigovian tax equivalent to US$974 per car would be equal to the marginal external cost of the traffic noise externality (noting that the optimal Pigovian tax is one that is equal to the marginal external cost). They also estimate the potential benefit of a move to 100 percent electric vehicles (which have lower engine noise) at US$5.39 billion for Florida, and $77.28 billion for the US as a whole.

This research tells us that traffic noise is a costly negative externality. Those costs are capitalised into property values and are borne disproportionately by lower-income households. Fortunately, the research also suggests that there are worthwhile ways of reducing those costs, including erecting noise barriers and rolling out more electric vehicles, and the benefits of those solutions may be substantial.

[HT: Marginal Revolution, last year]

Climate change and the tragedy of the commons

My ECONS102 class covered externalities and common resources this past week. In the final slide of content in my lectures, I talked about the challenges of getting global agreement on climate change, because the atmosphere's limited capacity to absorb emissions without causing harmful climate change provides a special case of the tragedy of the commons.

Why is climate change a common resource problem? Common resources are rival and non-excludable. The atmosphere's capacity to absorb emissions is both rival (one country's emissions reduce the capacity available for other countries) and non-excludable (if the capacity is reduced for one country, it is reduced for all countries). The social incentive is for all countries to reduce emissions to the point where the marginal social cost of emissions is equal to the marginal social benefit. The private incentive for each country is to reduce emissions only to where marginal private cost of emissions is equal to marginal private benefit for that country. Each country’s emissions impose a cost on other countries, meaning that each country doesn’t face the full cost of their emissions (so the marginal social cost of emissions is greater than the marginal private cost for each country), so they will emit too much. And since all countries have the same incentive, there are too many emissions relative to the socially optimal quantity.

Within a country, we might be able to solve a common resource problem like this by relying on the government to assign some form of property rights. However, there is no supra-national government to perform this role, so that means we need to arrive at a 'private solution' (albeit one where the private actors in the negotiation are countries).

The 2009 Nobel Prize winner Elinor Ostrom noted that users of a common resource may be able to solve the problem by working together (a common governance approach). A number of things would likely be necessary for such common governance to work. Ostrom noted a number of principles for common governance, one of which was that the boundary of the common resource and the group of users must be well-defined. In the case of climate change, the boundary is the environment, and the group of users is all countries. So, that principle would be no problem, provided all countries agreed to be involved (and that may be a challenge).

For common governance to be successful, the user community must also be relatively homogeneous, so that they can trust each other and develop common goals (and norms or customs) for protecting and allocating the resource. Here is where the challenge lies. The user community (countries) are not homogeneous at all. Countries at different levels of development have different goals and aspirations, and see the role of emissions in contributing to those goals and aspirations differently. And it seems unlikely that countries will really trust each other to do the right thing in relation to any climate agreement.

Ostrom also noted that protecting the resource would be best achieved through persuasion rather than coercion, since this would maintain trust within the user community. Persuading other sovereign countries to do something that makes them individually worse off is obviously a challenge. And so climate change remains one of humanity's greatest challenges. This isn't to say that it isn't an important challenge to solve, only that there are good reasons why, nearly 50 years on from the First World Climate Conference in Geneva in 1979, we are still looking for an effective agreement to protect the climate.

Don't just take my word for it though. This 2012 article by Niggol Seo (University of Sydney), published in the journal Economic Affairs (sorry, I don't see an ungated version online), outlines the case, supported by some estimates of the globally optimal policy (as it would have been at the time). Seo uses the model results to outline the incentives that each of thirteen world regions face in global negotiations over climate change. Seo compares a business-as-usual (BAU) scenario with a scenario based on the globally optimal policy (GOP). Focusing on the GOP scenario, the net costs of addressing climate change in that scenario for seven of the largest world regions are shown by Figure 2 from the paper:

Notice the large costs that China (green) and the US (blue) would face over the entire period up to the end of the century. It should be little wonder, then, that those two countries in particular would have less incentive to agree to emissions restrictions to address climate change. In contrast, the EU, India, Africa, Latin America, and Russia face more modest costs initially, and by 2075 (or 2065 in the case of Africa), the GOP scenario actually shows net benefits for those regions. Again, it should be little wonder that they have greater incentive to support of climate change agreements. Seo concludes that:

...some countries have a strong incentive to push for global regulation due to the expected reduction in climate related damages. The optimal regulation saves these countries hundreds of billions dollars annually by the century’s end. However, it would cause additional costs to China, Russia, Canada and the USA.

To that, I would observe that it particularly impacts China and the US. Climate change is a challenging problem. For an efficient global agreement that would adequately address this challenge, we need all countries to participate. However, the incentives do not necessarily help us to achieve cooperation.  Countries that face relatively low net costs from addressing climate change may need to offer transfers, concessions, technology, or some other form of compensation to countries that face high net costs, in order to change their incentives and get them on board. We may not think that outcome is fair. However, achieving an efficient and effective agreement may require some compromise on fairness, if that is what is needed to ensure that the incentives encourage all countries to participate.

Read more:

• Reason to be surprised, or not, about the Paris Agreement on climate change coming into force