When the smoke gets in your lungs: short-term effects of Indonesia's 2015 forest fires on health care use.

BACKGROUND: The forest fires that ravaged parts of Indonesia in 2015 were the most severely polluting of this century but little is known about their effects on health care utilization of the affected population. We estimate their short-term impact on visit rates to primary and hospital care with particular focus on visits for specific smoke-related conditions (respiratory disease, acute respiratory tract infection (ARTI) and common cold). METHOD: We estimate the short-term impact of the 2015 forest fire on visit rates to primary and hospital care by combining satellite data on Aerosol Optical Depth (AOD) with administrative records from Indonesian National Health Insurance Agency (BPJS Kesehatan) from January 2015-April  2016. The 16 months of panel data cover 203 districts in the islands of Sumatra and Kalimantan before, during and after the forest fires. We use the (more efficient) ANCOVA version adaptation of a fixed effects model to compare the trends in healthcare use of affected districts (with AOD value above 0.75) with control districts (AOD value below 0.75). Considering the higher vulnerability of children's lungs, we do this separately for children under 5 and the rest of the population adults (> 5), and for both urban and rural areas, and for both the period during and after the forest fires. RESULTS: We find little effects for adults. For young children we estimate positive effects for care related to respiratory problems in primary health care facilities in urban areas. Hospital care visits in general, on the other hand, are negatively affected in rural areas. We argue that these patterns arise because accessibility of care during fires is more restricted for rural than for urban areas. CONCLUSION: The severity of the fires and the absence of positive impact on health care utilization for adults and children in rural areas indicate large missed opportunities for receiving necessary care. This is particularly worrisome for children, whose lungs are most vulnerable to the effects. Our findings underscore the need to ensure ongoing access to medical services during forest fires and emphasize the necessity of catching up with essential care for children after the fires, particularly in rural areas.

Effects of performance-based capitation payment on the use of public primary health care services in Indonesia.

The Indonesian national health insurance agency BPJS Kesehatan, the largest single-payer system in the world, is among the first to combine capitation-based payments with performance-based financing. The Kapitasi Berbasis Komitmen (KBK) scheme for puskesmas (community health centres) was implemented in province capitals between August 2015 and May 2016. Its main goal was to incentivize the substitution of secondary by primary care use. We evaluate its effect on its three incentivized outcomes: the fraction of insured visiting the puskesmas, the fraction of chronically ill with a puskesmas visit and the hospital referral rate for insured with a non-specialistic condition. We use BPJS Kesehatan claims data from 2015 to 2016 from a stratified one percent sample of its members. Comparable control districts were identified using coarsened exact matching. We adopt a Difference-in-Differences (DID) study design and estimate a two-way fixed effects regression model to compare 27 intervention districts to 300 comparable non-capital control districts. We find that KBK payment increased the monthly percentage of enrolees contacting a puskesmas with 0.578 percentage points. This is a sizeable increase of 48 percent compared to the baseline rate of just 1.2% but it still leaves most puskesmas far below the "sufficient" KBK threshold of 15%. For chronically ill patients, a small increase of 1.15 percentage points was estimated, but it leaves the rate even further below the program's "sufficient" threshold of 50%. We find no statistically significant effect on referral rates to hospitals for conditions not requiring specialist care. While we find positive effects of KBK on two out of three outcomes, all estimated effect sizes leave the actual rates far below the program targets. Our findings suggest that the KBK performance-based capitation reform has not been very successful in substituting secondary care use by greater primary care use.

Has COVID-19 increased inequality in mortality by income in the Netherlands?

BACKGROUND: In the Netherlands in 2020, COVID-19 deaths were more concentrated among individuals with a lower income. At the same time, COVID-19 was a new cause that also displaced some deaths from other causes, potentially reducing income-related inequality in non-COVID deaths. Our aim is to estimate the impact of the COVID-19 pandemic on the income-related inequality in total mortality and decompose this into the inequality in COVID-attributed deaths and changes in the inequality in non-COVID causes. METHODS: We estimate excess deaths (observed minus trend-predicted deaths) by sex, age and income group for the Netherlands in 2020. Using a measure of income-related inequality (the concentration index), we decompose the inequality in total excess mortality into COVID-19 versus non-COVID causes. RESULTS: Cause-attributed COVID-19 mortality exceeded total excess mortality by 12% for the 65-79 age group and by about 35% for 80+ in the Netherlands in 2020, implying a decrease in the number of non-COVID deaths compared with what was predicted. The income-related inequality in all-cause mortality was higher than predicted. This increase in inequality resulted from the combination of COVID-19 mortality, which was more unequally distributed than predicted total mortality, and the inequality in non-COVID causes, which was less unequal than predicted. CONCLUSION: The COVID-19 pandemic has led to an increase in income-related inequality in all-cause mortality. Non-COVID mortality was less unequally distributed than expected due to displacement of other causes by COVID-19 and the potentially unequal broader societal impact of the pandemic.

The health impact of free access to antiretroviral therapy in South Africa.

Since 2004 the South African government has rolled out free antiretroviral therapy (ART) at public health care facilities nationwide. No prior studies have estimated the impact of the ART rollout on health and survival using a longitudinal household survey with national coverage. We match household member deaths and self-assessed health from a large national longitudinal survey to community-level ART availability in clinics to estimate the reduction in mortality and morbidity attributable to ART availability between 2006 and 2016, using a difference-in-difference model. Our analysis focuses on black Africans aged 25-49 because this demographic group represents more than two-thirds of all South African HIV cases. We find that the rollout of free ART has reduced annual mortality by 27% and decreased the likelihood of reporting poor health by 36% for black Africans aged 25-49. These estimates amount to annual reductions in this demographic category of 31% in annual mortality and 47% in individuals reporting poor health. Our findings confirm that making ART treatment freely available nationwide has had a dramatic impact in terms of both prolonged survival and improved health, with most of these gains concentrated in the high HIV prevalence group of black Africans aged 25-49.

Improving maternal and child health in Pakistan: a programme evaluation using a difference in difference analysis.

INTRODUCTION: Pakistan is a country with high maternal and infant mortality. Several large foreign funded projects were targeted at improving maternal, neonatal and child health. The Norway-Pakistan Partnership Initiative (NPPI) was one of these projects. This study aims to evaluate whether NPPI was successful in improving access and use of skilled maternal healthcare. METHODS: We used data from three rounds (2009-2010, 2011-2012 and 2013-2014) of the Pakistan Social and Living Standards Measurement Survey (PSLM). A difference-in-difference regression framework was used to estimate the effectiveness of NPPI and its different programme components with respect to maternal healthcare seeking behaviour of pregnant women. Various parts of the PSLM were combined to examine the healthcare seeking behaviour response of pregnant women to exposure to NPPI. RESULTS: Trends in maternal care seeking behaviour of pregnant women were similar in districts exposed to NPPI and control districts. Consequently, only a weak and insignificant impact of NPPI on maternal care seeking behaviour was found. However, women in districts which used vouchers or which implemented contracting were more likely to seek skilled assistance with their delivery. CONCLUSION: We conclude that the objective to improve access to and use of skilled care was not achieved by NPPI. The small effects identified for vouchers and contracts on skilled birth attendance hold some promise for further experimentation.

Association Between Income and Perinatal Mortality in the Netherlands Across Gestational Age.

Importance: The association between household income and perinatal health outcomes has been understudied. Examining disparities in perinatal mortality within strata of gestational age and before and after adjusting for birth weight centile can reveal how the income gradient is associated with gestational age, birth weight, and perinatal mortality. Objectives: To investigate the association between household income and perinatal mortality, separately by gestational age strata and time of death, and the potential role of birth weight centile in mediating this association. Design, Setting, and Participants: This cross-sectional study used individually linked data of all registered births in the Netherlands with household-level income tax records. Singletons born between January 1, 2004, and December 31, 2016, at 24 weeks to 41 weeks 6 days of gestation with complete information on birth outcomes and maternal characteristics were studied. Data analysis was performed from March 1, 2018, to August 30, 2021. Exposures: Household income rank (adjusted for household size). Main Outcomes and Measures: Perinatal mortality, stillbirth (at ≥24 weeks of gestation), and early neonatal mortality (at ≤7 days after birth). Disparities were expressed as bottom-to-top ratios of projected mortality among newborns with the poorest 1% of households vs those with the richest 1% of households. Generalized additive models stratified by gestational age categories, adjusted for potential confounding by maternal age at birth, maternal ethnicity, parity, sex, and year of birth, were used. Birth weight centile was included as a potential mediator. Results: Among 2 036 431 singletons in this study (1 043 999 [51.3%] males; 1 496 579 [73.5%] with mother of Dutch ethnicity), 121 010 (5.9%) were born before 37 weeks of gestation, and 8720 (4.3 deaths per 1000) died during the perinatal period. Higher household income was positively associated with higher rates of perinatal survival, with an unadjusted bottom-to-top ratio of 2.18 (95% CI, 1.87-2.56). The bottom-to-top ratio decreased to 1.30 (95% CI, 1.22-1.39) after adjustment for potential confounding factors and inclusion of birth weight centile as a possible mediator. The fully adjusted ratios were lower for stillbirths (1.27; 95% CI, 1.20-1.36) than for early neonatal deaths (1.35; 95% CI, 1.14-1.66). Inequalities in perinatal mortality were found for newborns at greater than 26 weeks of gestation but not between 24 and 26 weeks of gestation (fully adjusted bottom-to-top ratio, 0.89; 95% CI, 0.77-1.04). Conclusions and Relevance: The results of this large nationally representative cross-sectional study suggest that a large part of the increased risk of perinatal mortality among low-income women is mediated via a lower birth weight centile. The absence of disparities at very low gestational ages suggests that income-related risk factors for perinatal mortality are less prominent at very low gestational ages. Further research should aim to understand which factors associated with preterm birth and lower birth weight can reduce inequalities in perinatal mortality.

Who is more likely to return for TB test results? A survey at three high-burden primary healthcare facilities in Cape Town, South Africa.

BACKGROUND: In low- and middle-income countries with a high burden of tuberculosis (TB), a large proportion of people who are tested for TB do not return to the health facility to collect their test results and initiate treatment, thus putting themselves at increased risk of adverse outcomes. METHODS: This prospective study aimed to identify predictors of returning to the primary health care (PHC) facility to collect TB test results. From 15 August to 15 December 2017, 1105 people who tested for pulmonary TB at three Cape Town PHC facilities were surveyed. Using multi-variate logistic regressions on an analysis sample of 1097 people, three groups of predictors were considered: (i) demographics, health and socio-economic status; (ii) costs and benefits; and (iii) behavioural factors. RESULTS: Forty-four percent of people tested returned to the PHC facility to collect their test results within the stipulated 2 days, and 68% returned before the end of the study period. Return was strongly and positively correlated with expecting a TB-positive result, cognitive avoidance and postponement behaviour. CONCLUSION: Interventions to improve pre-treatment loss to follow-up should target patients who think they do not have TB, and those with a history of postponement behaviour and cognitive avoidance.

Inequality in mortality between Black and White Americans by age, place, and cause and in comparison to Europe, 1990 to 2018.

Although there is a large gap between Black and White American life expectancies, the gap fell 48.9% between 1990 and 2018, mainly due to mortality declines among Black Americans. We examine age-specific mortality trends and racial gaps in life expectancy in high- and low-income US areas and with reference to six European countries. Inequalities in life expectancy are starker in the United States than in Europe. In 1990, White Americans and Europeans in high-income areas had similar overall life expectancy, while life expectancy for White Americans in low-income areas was lower. However, since then, even high-income White Americans have lost ground relative to Europeans. Meanwhile, the gap in life expectancy between Black Americans and Europeans decreased by 8.3%. Black American life expectancy increased more than White American life expectancy in all US areas, but improvements in lower-income areas had the greatest impact on the racial life expectancy gap. The causes that contributed the most to Black Americans' mortality reductions included cancer, homicide, HIV, and causes originating in the fetal or infant period. Life expectancy for both Black and White Americans plateaued or slightly declined after 2012, but this stalling was most evident among Black Americans even prior to the COVID-19 pandemic. If improvements had continued at the 1990 to 2012 rate, the racial gap in life expectancy would have closed by 2036. European life expectancy also stalled after 2014. Still, the comparison with Europe suggests that mortality rates of both Black and White Americans could fall much further across all ages and in both high-income and low-income areas.

In Appreciation of Adam: Reflections from Friends and Colleagues.

Some of Adam Wagstsaff's colleagues and research collaborators submitted short reflections about the different ways Adam made a difference through his amazing research output to health equity and health systems as well as a leader and mentor. The Guest Editors of this Special Issue selected a set of six essays related to dimensions of Adam's contributions.The first contribution highlights his role early on in his career, prior to joining the World Bank, in defining and expanding an important field of research on equity in health ("Adam and Equity," by Eddy van Doorslaer and Owen O'Donnell). The second contribution focuses on Adam's early work on equity and health within the World Bank and his leadership on important initiatives that have had impact far beyond the World Bank ("Adam and Health Equity at the World Bank," by Davidson Gwatkin and Abdo Yazbeck). The next contribution focuses on Adam's deep dive into providing support, through research, for country-specific programs and reforms, with a special focus on some countries in East Asia ("Adam and Country Health System Research," by Magnus Lindelow, Caryn Bredenkamp, Winnie Yip, and Sarah Bales). The next contribution highlights Adam's many ways of contributing to the International Health Economics Association, from the impressive technical contributions to leadership and organizational reform ("Adam and iHEA," by Diane McIntyre). The next to last contribution focuses on Adam's long-term leadership in the research group at the World Bank and the long-lasting influence on integrating the research produced into World Bank operations and creating an environment that rewarded producing evidence for action ("Adam the Research Manager," by Deon Filmer and Damien de Walque). The last contribution pulls on the thread found in many of the earlier ones, mentorship with honesty, directness, caring, commitment, and equity ("Adam the Mentor," by Agnes Couffinhal, Caryn Bredenkamp, and Reem Hafez).

Changing Inequalities in Health-Adjusted Life Expectancy by Income and Race in South Africa.

Trends in socioeconomic-related health inequalities is a particularly pertinent topic in South Africa where years of systematic discrimination under apartheid bequeathed a legacy of inequalities in health outcomes. We use three nationally representative datasets to examine trends in income- and race-related inequalities in life expectancy (LE) and health-adjusted life expectancy (HALE) since the beginning of the millennium. We find that, in aggregate, (HA)LE at age five fell substantially between 2001 and 2007, but then increased to above 2001 levels by 2016, with the largest changes observed among prime age adults. Income- and race-related inequalities in both LE and HALE favor relatively well-off and non-Black South Africans in all survey years. Both income- and race-related inequalities in (HA)LE grew between 2001 and 2007, and then narrowed between 2007 to 2016. However, while race-related inequalities in (HA)LE in 2016 were smaller than in 2001, income-related inequalities in (HA)LE were greater in 2016 than in 2001. Based on the patterns and timing observed, these trends in income- and race-related inequalities in (HA)LE are most likely related to the delayed initial policy response to the HIV epidemic, the subsequent rapid and effective rollout of anti-retroviral therapy, and the changes in the overall income distribution among Black South Africans. In particular, the growth of the Black middle class narrowed the HA(LE) gap with the non-Black population but reinforced income-related inequalities.

The relative importance and stability of disease burden causes over time: summarizing regional trends on disease burden for 290 causes over 28 years.

BACKGROUND: Since the Global Burden of Disease study (GBD) has become more comprehensive, data for hundreds of causes of disease burden, measured using Disability Adjusted Life Years (DALYs), have become increasingly available for almost every part of the world. However, undergoing any systematic comparative analysis of the trends can be challenging given the quantity of data that must be presented. METHODS: We use the GBD data to describe trends in cause-specific DALY rates for eight regions. We quantify the extent to which the importance of 'major' DALY causes changes relative to 'minor' DALY causes over time by decomposing changes in the Gini coefficient into 'proportionality' and 'reranking' indices. RESULTS: The fall in regional DALY rates since 1990 has been accompanied by generally positive proportionality indices and reranking indices of negligible magnitude. However, the rate at which DALY rates have been falling has slowed and, at the same time, proportionality indices have tended towards zero. These findings are clearest where the focus is exclusively upon non-communicable diseases. Notably, large and positive proportionality indices are recorded for sub-Saharan Africa over the last decade. CONCLUSION: The positive proportionality indices show that disease burden has become less concentrated around the leading causes over time, and this trend has become less prominent as the DALY rate decline has slowed. The recent decline in disease burden in sub-Saharan Africa is disproportionally driven by improvements in DALY rates for HIV/AIDS, as well as for malaria, diarrheal diseases, and lower respiratory infections.

Does geographic spending variation exacerbate healthcare benefit inequality? A benefit incidence analysis for Indonesia.

The Indonesian government has made some ambitious steps to achieve Universal Health Coverage through the newly formed National Health Insurance [Jaminan Kesehatan Nasional (JKN)], establishing a single-payer insurance agency and prospective provider payment mechanism. This study aims to assess the benefit incidence of healthcare funding in the JKN era, and its distribution by socio-economic status considering regional variation in unit costs. We evaluate whether the benefit incidence of funding is skewed towards urban and wealthier households. We also investigate whether standard benefit incidence analysis using national unit costs underestimates regional disparities in healthcare funding. Lastly, we examine whether the design of the JKN provider payment system exacerbates regional inequalities in healthcare funding and treatment intensity. The analysis relies on Indonesia's annual National Socio-economic Survey (Susenas) and administrative data on JKN provider payments from 2015 to 2017, combined at district level for 466 districts. We find that the benefit incidence of healthcare expenditure favours the wealthier groups. We also observe substantial variation in hospital unit costs across regions in Indonesia. As a result, standard benefit incidence analysis (using national average unit transfers) underestimates the inequality due to regional disparities in healthcare supply and intensity of treatment. The JKN provider payment seems to favour relatively wealthier regions that harbour more advanced healthcare services. Urban dwellers and people living in Java and Bali also enjoy greater healthcare benefit incidence compared to rural areas and the other islands.

Health Care Use and Out-of-pocket Spending by Persons With Dementia Differ Between Europe and the United States.

BACKGROUND: Persons with dementia need much care, but what care is used and how the burden of financing is divided between persons with dementia, caregivers, and public programs may differ between countries. OBJECTIVE: The objective of this study was to compare how health care use and out-of-pocket (OOP) spending associated with dementia differ between the United States and Europe, with and without controlling for background characteristics. RESEARCH DESIGN: We use prospectively collected survey data from the United States-based Health and Retirement Study (n=48,877) and the Survey of Health, Ageing, and Retirement in Europe (n=98,971) including all adults over the age of 70 years. Dementia status is imputed using a validated algorithm. After first reporting the observed differences in care use, we analyze how care use is associated with dementia using multivariate regressions, controlling for other health conditions and background characteristics. RESULTS: Persons with dementia in the United States use 50% less formal home care per year than persons living with dementia in Europe [mean (SD)=236.8 h (1047.4) vs. 463.3 h (1371.2)], but use more nursing home care [75.1 d (131.4) vs. 45.5 d (119.4)). Dementia is associated with higher OOP spending in the United States than Europe [4406 USD (95% confidence interval, 3914-4899) vs. 246 USD (73-418)-2017 price levels]. CONCLUSIONS: Health care use and OOP spending differ between Europe and the United States. The far greater reliance on nursing home care in the United States likely causes much higher expenditures for people with dementia and insurance programs alike.

Death by austerity? The impact of cost containment on avoidable mortality in Italy.

Does austerity in health care affect health and healthcare outcomes? We examine the intended and unintended effects of the Italian austerity policy Piano di Rientro aimed at containing the cost of the healthcare sector. Using an instrumental variable strategy that exploits the temporal and geographical variation induced by the policy rollout, we find that the policy was successful in alleviating deficits by reducing expenditure, mainly in the southern regions, but also resulted in a 3% rise in avoidable deaths among both men and women, a reduction in hospital capacity and a rise in south-to-north patient migration. These findings suggest that-even in a high-income country with relatively low avoidable mortality like Italy-spending cuts can hurt survival.

Eligibility or use? Disentangling the sources of horizontal inequity in home care receipt in the Netherlands.

We study horizontal inequity in home care use in the Netherlands, where a social insurance scheme aims to allocate long-term care according to care needs. Whether the system reaches its goal depends not only on whether eligible individuals have equal access to care but also on whether entitlements for care reflect needs, irrespective of socioeconomic status and other characteristics. We assess and decompose total inequity into inequity in (i) entitlements for home care and (ii) the conversion of these entitlements into actual use. This distinction is original and important, because inequity calls for different policy responses depending on the stage at which it arises. Linking survey and administrative data on the 65 and older, we find higher income elderly to receive less home care than poorer elderly with similar needs. Although lower income elderly tend to make greater use of their entitlements, need-standardized entitlements are similar across income, education, and wealth levels. However, both use and entitlements vary by origin and place of residence. The Dutch need assessment seems effective at restricting socioeconomic inequity in home care use but may not fully prevent inequity along other dimensions. Low financial barriers and universal eligibility rules may help achieve equity in access but are not sufficient conditions.

Better off at home? Effects of nursing home eligibility on costs, hospitalizations and survival.

Encouraging and helping elderly to postpone a nursing home admission appears to be a win-win that keeps long-term care spending in check and is in line with the target population's preferences, but there is little evidence about its effects. We study the causal impact of nursing home admission eligibility using Dutch administrative data and exploiting variation between randomly assigned assessors in their tendency to grant eligibility for a nursing home admission. We find a drop in medical care use when eligibility is granted, especially in hospital admissions, while total healthcare spending is unaffected. This suggests that postponing an admission may not always be a win-win after all.

Does price deregulation in a competitive hospital market damage quality?

Regulators may be hesitant to permit price competition in healthcare markets because of its potential to damage quality. We assess whether this fear is well founded by examining a reform that permitted Dutch health insurers to freely negotiate prices with hospitals. Unlike previous research on hospital competition that has relied on quality indicators for urgent treatments, we take advantage of a plausible absence of selection bias to identify the effect on the quality of elective procedures that should be more price responsive. Using data on all admissions for hip replacements to Dutch hospitals and a difference-in-differences comparison between more and less concentrated markets, we find no evidence that price deregulation in a competitive environment reduces quality measured by hip replacement readmission rates.

Thank goodness for stickiness: Unravelling the evolution of income-related health inequalities before and after the Great Recession in Europe.

The Great Recession in Europe sparked concerns that the crisis would lead to increased income related health inequalities (IRHI). Did this come to pass, and what role, if any, did government transfers play in the evolution of these inequalities? Motivated by these questions, this paper seeks to (i) study the evolution of IRHI during the crisis, and (ii) decompose these evolutions to examine the separate roles of government versus market transfers. Using panel data for 7 EU countries from 2004 to 2013, we find no evidence that IRHI persistently rose after 2008, even in countries most affected by the crisis. Our decomposition reveals that, while the health of the poorest did indeed worsen during the crisis, IRHI were prevented from increasing by the relative stickiness of old age pension benefits compared to the market incomes of younger groups. Austerity measures weakened the IRHI reducing effect of government transfers.

Equal long-term care for equal needs with universal and comprehensive coverage? An assessment using Dutch administrative data.

The Netherlands is one of the few countries that offer generous universal public coverage of long-term care (LTC). Does this ensure that the Dutch elderly with similar care needs receive similar LTC, irrespective of their income? In contrast with previous studies of inequity in care use that relied on a statistically derived variable of needs, our paper exploits a readily available, administrative measure of LTC needs stemming from the eligibility assessment organized by the Dutch LTC assessment agency. Using exhaustive administrative register data on 616,934 individuals aged 60 and older eligible for public LTC, we find a substantial pro-poor concentration of LTC use that is only partially explained by poorer individuals' greater needs. Among those eligible for institutional care, higher-income individuals are more likely to use-less costly-home care. This pattern may be explained by differences in preferences, but also by their higher copayments for nursing homes and by greater feasibility of home-based LTC arrangements for richer elderly. At face value, our findings suggest that the Dutch LTC insurance "overshoots" its target to ensure that LTC is accessible to poorer elderly. Yet, the implications depend on the origins of the difference and one's normative stance.

The kids are alright - labour market effects of unexpected parental hospitalisations in the Netherlands.

Unexpected negative health shocks of a parent may reduce adult children's labour supply via informal caregiving and stress-induced mental health problems. We link administrative data on labour market outcomes, hospitalisations and family relations for the full Dutch working age population for the years 1999-2008 to evaluate the effect of an unexpected parental hospitalisation on the probability of employment and on conditional earnings. Using an event study difference-in-differences model combined with coarsened exact matching and individual fixed effects, we find no effect of an unexpected parental hospitalisation on either employment or earnings for Dutch men and women, and neither for the full population nor for the subpopulations most likely to become caregivers. These findings suggest that the extensive public coverage of formal long-term care in the Netherlands combined with widespread acceptance of part-time work provides sufficient opportunities to deal with adverse health events of family members without having to compromise one's labour supply.