Time-invariant Characteristics Research Articles

Food insufficiency, depression, and the modifying role of social support: Evidence from a population-based, prospective cohort of pregnant women in peri-urban South Africa

RationaleFood insecurity has emerged as an important, and potentially modifiable, risk factor for depression. Few studies have brought longitudinal data to bear on investigating this association in sub-Saharan Africa. ObjectiveTo estimate the association between food insufficiency and depression symptom severity, and to determine the extent to which any observed associations were modified by social support. Methods and resultsWe conducted a secondary analysis of population-based, longitudinal data collected from 1238 pregnant women during a three-year cluster-randomized trial of a home visiting intervention in Cape Town, South Africa. Surveys were conducted at baseline, 6 months, 18 months, and 36 months (85% retention). A validated, single-item food insufficiency measure inquired about the number of days of hunger in the past week. Depression symptom severity was measured using the Xhosa version of the 10-item Edinburgh Postnatal Depression Scale. In multivariable regression models with cluster-correlated robust estimates of variance, lagged food insufficiency had a strong and statistically significant association with depression symptom severity (β = 0.70; 95% CI, 0.46–0.94), suggesting a 6.5% relative difference in depression symptom severity per day of hunger. In stratified analyses, food insufficiency had a statistically significant association with depression only among women with low levels of instrumental support. Using quantile regression, we found that the adverse impacts of food insufficiency were experienced to a greater degree by women in the upper end of the conditional distribution of depression symptom severity. Estimates from fixed-effects regression models and fixed-effects quantile regression models, accounting for unobserved confounding by time-invariant characteristics, were similar. ConclusionsFood insufficiency was associated with depression symptom severity, particularly for women in the upper end of the conditional depression distribution. Instrumental social support buffered women against the adverse impacts of food insufficiency.

Professional Networks and Client Tax Avoidance: Evidence from the Italian Statutory Audit Regime

Under the Italian statutory audit regime, three individual accountants are appointed to jointly audit each client. Working together on multiple engagements, individual auditors form professional networks that can be conduits of knowledge spillover. We use network measures of centrality to capture auditors’ ability to acquire and apply expertise across engagements. We demonstrate that clients engaging better-connected individual auditors have comparatively lower effective tax rates. Our results are robust to controlling for characteristics of the client, individual auditor, and auditor’s firm, as well as audit quality and fees. Moreover, we use individual auditor fixed effects to examine the effect of time-invariant individual auditor characteristics. Our fixed effects analyses indicate that both time-invariant individual auditor characteristics and changes in auditor centrality over time are associated with client tax outcomes. Our findings suggest that an environment encouraging individual cross-appointments over multiple engagements can facilitate the transfer of expertise between members of professional teams.

The Impact of Trade Agreements: New Approach, New Insights

The Trans-Pacific Partnership (TPP) has reinvigorated research on the ex-ante impact of trade agreements. The results from these ex-ante models are subject to considerable uncertainties, and needs to be complimented by ex-post studies. The paper fills this gap in recent literature by employing synthetic control methods (SCM) – currently extremely popular in micro and macro studies – to understand the impact of trade agreements in the period 1983–1995 for 104 country pairs. The key advantage of using SCM to address selection bias – one of the persisting issues in trade literature – is that it allows the effect of unobserved confounder to vary with time, as opposed to traditional econometric methods that can deal with time-invariant unobserved country characteristics. Using SCM approach, the paper finds that trade agreements can generate substantial gains, on average an increase of exports by 80 percentage points over ten years. The export gains are higher when emerging markets have trade agreements with advanced markets. The paper shows that all the countries in NAFTA have substantially gained due to NAFTA. Finally, there is some evidence that trade agreements can potentially lead to slight import diversion, but not export diversion.

Differences in polysubstance use among youth in the child welfare system: Toward a better understanding of the highest-risk teens

The current study extended limited prior work on polysubstance use among youth in the child welfare system (CWS) by addressing their potentially greater risk of engaging in polysubstance use, the causes of interpersonal variation in use, and changes in use over time, particularly at later points of involvement in the CWS. Using longitudinal data from the National Survey of Child and Adolescent Well-Being (n=1,178), a series of time-invariant and time-varying demographic and contextual factors were explored to assess their role both overall and at unique points of involvement in the CWS. A series of unconditional and conditional curve-of-factor models were estimated and results indicated that time-invariant characteristics of ethnicity and gender were not related to polysubstance use. Time-variant characteristics of age and placement were associated with polysubstance use and highlighted the dynamic nature of age as a risk factor. Out-of-home placement was protective against later substance use for youth who had been removed from contexts with their original caretaker where there were higher levels of reported violence. Our results suggest that in the child welfare population, the modeling of multiple substances rather than a single substance in isolation is more informative because it yields information on the confluence of behaviors that tend to occur and evolve together.

A Longitudinal Analysis of Violence and Housing Insecurity

Violence and housing insecurity are horrible events that may be intertwined, with violence possibly forcing victims to abandon their accommodations and housing insecurity depriving people of the safety of a home or placing them in compromised circumstances. This study uses national, prospective, longitudinal data from the Journeys Home Survey to examine how violence, housing insecurity, and other characteristics in one period affect disadvantaged Australian men’s and women’s chances of experiencing violence and housing insecurity in subsequent periods. The study is one of the first to investigate these relationships prospectively and unusual in considering how violence among adult men contributes to their housing insecurity. We estimate dynamic multivariate models that control for observed and time-invariant unobserved characteristics and find that men’s chances of being housing secure without experiencing violence are 24-45 percent lower and women’s chances are 12-20 percent lower if they experienced housing insecurity, violence or both in the previous period. Heavy drinking, marijuana use, psychological distress, and a history of childhood abuse and neglect also increase the risks of violence and housing insecurity for both genders, while the presence of children reduces these risks. Women who are bisexual or lesbian and women with homeless friends also face elevated risks of housing insecurity, while men’s sexual orientation and friend networks seem less relevant.

Panel Quantile Regressions and the Subjective Well-Being in Urban China: Evidence from RUMiC Data

Using RUMiC data and a simple panel quantile regression method, this paper accounts for the time-invariant individual specific characteristics and investigates the heterogeneous effects of factors on the distribution of subjective well-being (SWB, measured by GHQ-12) in urban China. Comparing results from the pooled regression and fixed effect regression, we find that most results from pooled regressions are likely overestimated. Panel quantile regression results show that income affects the least happy 10 % group twice as much as the happiest 10 % people. Being unemployed brings down the happiness level by 0.97 points on average, but individuals with high SWB seem to be not significantly affected. The complete picture of the relationship between SWB and various factors would have been veiled without using quantile techniques. This paper therefore not only contributes to the happiness literature in China, but also adds evidence to stylized findings going beyond the average.

Association Between Sedentary Work and BMI in a U.S. National Longitudinal Survey.

Technological advancements have made life and work more sedentary, and long hours of sitting are known to be associated with many health concerns. Several studies have reported an association between prolonged sitting time at work and weight gain, but the results are inconsistent. This study examined the relationship between sitting time at work and BMI using data from a large prospective cohort of U.S. men and women from 2002 to 2010. Initial analyses were performed in 2013, with additional analyses in 2014 and 2015. The sample size at the base year (2002) was 5,285 and the age range 38-45 years. The outcome, BMI, was based on self-reported measures of height and weight. Estimates of workplace sitting time were linked from an external database (Occupational Information Network), and the occupation-wide rating for sitting time was linked to survey participants by occupation. Fixed-effects models controlling for time-invariant effects of all time-invariant characteristics were employed to examine the association, controlling for age, education, work hours, and hours of vigorous and light/moderate physical activities. Longer sitting time was significantly associated with higher BMI for the overall sample (β = 0.054; p<0.05) and men (β = 0.086; p<0.01). For women, the association was not statistically significant. The findings provide further support for initiatives to reduce workplace sitting time as a means of reducing the risk of weight gain and related health conditions.

Exchange Rate Fluctuations and the Margins of Exports

This paper examines the relationship between exchange rate fluctuations and New Zealand export performance. To isolate the impact of the exchange rate, as opposed to contemporaneous (and related) fluctuations in New Zealand's economic performance or overseas market characteristics, we focus on bilateral export relationships at the firm level and control for both time-invariant country characteristics and changes in aggregate economic conditions. We examine two key margins of export adjustment – the probability of exporting (the extensive margin) and the average value of exports per firm (the intensive margin) – and distinguish between impacts on market incumbents and new or potential entrants. Finally, we specifically take account of the potential for interaction between the level and volatility of the exchange rate to affect exporting, as implied by theories of exchange rate hysteresis.

Association between medical home enrollment and health care utilization and costs among breast cancer patients in a state Medicaid program.

The patient-centered medical home (PCMH) is increasingly being implemented in an effort to improve and coordinate primary care, but its effect on health care utilization among breast cancer patients remains unclear. The objective of this study was to examine health care utilization and expenditures as a function of PCMH enrollment among breast cancer patients in North Carolina's Medicaid program. North Carolina Medicaid claims linked to North Carolina Central Cancer Registry records (2003-2007) were used to examine monthly patterns of health care use and expenditures. Controlling for a selection bias for time-invariant characteristics, fixed effects regression models analyzed associations between PCMH enrollment and utilization of outpatient, inpatient, and emergency department (ED) services and Medicaid expenditures during the 15 months after the diagnosis of breast cancer. Among 758 breast cancer patients, 381 (50%) were enrolled in a PCMH at some time in the 15 months after diagnosis. After controlling for individual fixed effects, PCMH enrollment was significantly associated with greater outpatient service use, but there was no difference in the probability of inpatient hospitalizations or ED visits. Enrollment in a PCMH was associated with increased average expenditures of $429 per month during the first 15 months. Greater outpatient care utilization and increased average expenditures among breast cancer patients enrolled in a PCMH may suggest that these women have improved access to primary and specialty care. Expanding PCMHs may change patterns of service utilization for Medicaid breast cancer patients but may not be associated with lower costs.

Childhood Obesity and Cognitive Achievement.

Obese children tend to perform worse academically than normal-weight children. If poor cognitive achievement is truly a consequence of childhood obesity, this relationship has significant policy implications. Therefore, an important question is to what extent can this correlation be explained by other factors that jointly determine obesity and cognitive achievement in childhood? To answer this question, we exploit a rich longitudinal dataset of Australian children, which is linked to national assessments in math and literacy. Using a range of estimators, we find that obesity and body mass index are negatively related to cognitive achievement for boys but not girls. This effect cannot be explained by sociodemographic factors, past cognitive achievement or unobserved time-invariant characteristics and is robust to different measures of adiposity. Given the enormous importance of early human capital development for future well-being and prosperity, this negative effect for boys is concerning and warrants further investigation.

Suicide and Ambient Temperature in East Asian Countries: A Time-Stratified Case-Crossover Analysis.

BackgroundA limited number of studies suggest that ambient temperature contributes to suicide; these studies typically focus on a single nation and use temporally and spatially aggregated data.ObjectiveWe evaluated the association between ambient temperature and suicide in multiple cities in three East Asian countries.MethodsA time-stratified case-crossover method was used to explore the relationship between temperature and suicide, adjusting for potential time-varying confounders and time-invariant individual characteristics. Sex- and age-specific associations of temperature with suicide were estimated, as were interactions between temperature and these variables. A random-effects meta-analysis was used to estimate country-specific pooled associations of temperature with suicide.ResultsAn increase in temperature corresponding to half of the city-specific standard deviation was positively associated with suicide in most cities, although average suicide rates varied substantially. Pooled country-level effect estimates were 7.8% (95% CI: 5.0, 10.8%) for a 2.3°C increase in ambient temperature in Taiwan, 6.8% (95% CI: 5.4, 8.2%) for a 4.7°C increase in Korea, and 4.5% (95% CI: 3.3, 5.7%) for a 4.2°C increase in Japan. The association between temperature and suicide was significant even after adjusting for sunshine duration; the association between sunshine and suicide was not significant. The associations were greater among men than women in 12 of the 15 cities although not significantly so. There was little evidence of a consistent pattern of associations with age. In general, associations were strongest with temperature on the same day or the previous day, with little evidence of associations with temperature over longer lags (up to 5 days).ConclusionsWe estimated consistent positive associations between suicide and elevated ambient temperature in three East Asian countries, regardless of country, sex, and age.CitationKim Y, Kim H, Honda Y, Guo YL, Chen BY, Woo JM, Ebi KL. 2016. Suicide and ambient temperature in East Asian countries: a time-stratified case-crossover analysis. Environ Health Perspect 124:75–80; http://dx.doi.org/10.1289/ehp.1409392

The Relationship between Medicare Payment and Service Volume for Retina Procedures from 2005 through 2009

To calculate the relationship between Medicare payment and service volume for the 3 highest-volume retina procedures: intravitreal injection (Current Procedural Terminology [CPT] code 67028), laser treatment for retinal edema (CPT code 67210), and laser treatment for proliferative retinopathy (CPT code 67228). Retrospective, longitudinal database study. One hundred percent dataset of all retina procedures performed on Medicare Part B beneficiaries within the United States from 2005 through 2009. Fixed-effects regression model using Medicare Part B carrier data for all 50 states and the District of Columbia, controlling for time-invariant carrier-specific characteristics, national trends in service volume, Medicare beneficiary population, number of ophthalmologists, and income per capita. Medicare payment-service volume elasticities, defined as the percent change in service volume per 1% change in Medicare payment, for intravitreal injection, laser treatment for retinal edema, and laser treatment for proliferative retinopathy. For all 3 retina procedures, the regression coefficients representing the Medicare payment-service volume elasticity were nonsignificant: intravitreal injection elasticity, -0.75 (95% confidence interval [CI], -1.62 to 0.13; P = 0.09); laser treatment for retinal edema elasticity, 0.14 (95% CI, -0.38 to 0.65; P = 0.59); and laser treatment for proliferative retinopathy elasticity, 0.05 (95% CI, -0.26 to 0.35; P = 0.77). This study found no evidence suggesting that there is an association between Medicare payment and service volume for the 3 highest-volume retina procedures from 2005 through 2009.

The effect of foreign management and board membership on the performance of foreign acquired Turkish banks

Purpose– The purpose of this paper is to explore the effects of appointing foreign directors on the foreign acquired Turkish banks. Based on the developments in the Turkish banking system and the distinctive features of the Turkish market, the authors examine the appointment of foreign directors in three different levels: as a CEO, chairman and board member. The authors analyse how the appointments of foreign directors in each of these three levels affects the profitability and strategies of foreign acquired banks.Design/methodology/approach– The authors use the difference-in-difference (DID) model where the authors compare two groups: foreign acquired banks vs domestic banks for a five-year period. By applying the DID model, the authors aim to remove the time invariant individual characteristics of the banks that could be due to the permanent differences between the two groups, as well as biases from comparisons over time that could be due to trends.Findings– The authors find that the presence of the foreign chairman has a positive effect on the profitability of the foreign acquired bank and on the improvement of the income generated from interest activities, indicating that foreign chairman improves the monitoring of board of directors and brings new skills and experiences. Furthermore, foreign acquired banks are associated with an increase in the income generated from non-interest activities in the fifth year following their acquisitions, showing the introduction of new strategies. The change of the foreign acquired bank’s strategies in the fifth year after acquisition also suggests that it takes time to implement new strategies in a new environment.Originality/value– Though the effects of foreign board membership on bank’s performance have been previously discussed in literature, this study differentiates in that it distinguishes among different positions, e.g. chairman or CEO when examining the effect of a foreign director on a foreign acquired bank’s performance. In addition, the use of foreign acquired Turkish banks in the sample in this context adds to the general academic literature.

The Gender Unemployment Gap: How the 2008–2009 Economic Crisis in Ecuador Differentially Affected Women

This paper uses panel data to assess how the 2008–2009 economic crisis affected the unemployment rates of Ecuadorian men and women differently. After controlling for individual characteristics, the results of a difference-in-differences model and individual and household fixed effects models indicate that women were one to two percentage points more likely than men to be unemployed during the economic crisis in Ecuador. This paper concludes, therefore, that the economic crisis negatively affected women more than men even after controlling for observed and unobserved time-invariant individual characteristics.

Pick Your Poison: The Choices and Consequences of Policy Responses to Crises

Countries choose different strategies when responding to crises. An important challenge in assessing the impact of these policies is selection bias with respect to relatively time-invariant country characteristics, as well as time-varying values of outcome variables and other policy choices. This paper addresses this challenge by using propensity-score matching to estimate how major reserve sales, large currency depreciations, substantial changes in policy interest rates, and increased controls on capital outflows affect real GDP growth, unemployment, and inflation during two periods marked by crises, 1997–2001 and 2007–11. We find that none of these policies yield significant improvements in growth, unemployment, and inflation. Instead, a large increase in interest rates and new capital controls are estimated to cause a significant decline in GDP growth. Sharp currency depreciations may raise GDP growth over time, but only with a lagged effect and after an initial contraction.

Injury prevention by medication among children with attention-deficit/hyperactivity disorder: a case-only study.

Children and adolescents with attention-deficit/hyperactivity disorder (ADHD) have an increased risk of injuries. Attention-deficit/hyperactivity disorder is often treated with medication, but the evidence regarding prevention of injuries is inconclusive. To determine via a case-only design whether the use of methylphenidate hydrochloride or atomoxetine hydrochloride reduces the risk of injuries among children and adolescents with ADHD. We used the German Pharmacoepidemiological Research Database, which includes records from about 17 million insurees (approximately 20% of the population) from 4 statutory health insurance providers in Germany to identify children aged 3 to 17 years with new diagnoses of ADHD in 2005 and 2006. We identified 37,650 children with ADHD based on inpatient and outpatientdiagnostic codes (F90.0, F90.1, and F90.9) from the German modification of the International Statistical Classification of Diseases and Related Health Problems, 10th Revision. Among them, we identified those with an inpatient injury diagnosis during follow-up until 2009. A total of 2128 children with any injury diagnosis at hospitalization, 821 of whom had a brain injury diagnosis, were included in the analysis. We applied the self-controlled case series design to control for time-invariant characteristics of the patients and time trends in the exposure. Treatment with methylphenidate or atomoxetine based on prescription data. Hospitalization because of any injury or brain injury according to the injury mortality diagnosis matrix. Incidence rate ratios for the periods with medication compared with nonmedicated periods were 0.87 (95% CI, 0.74-1.02) for hospitalization with any injuries and 0.66 (95% CI, 0.48-0.91) for brain injuries only in the full sample. These estimates remained stable in sensitivity analyses restricting the sample to a narrower age range or to patients with a single hospitalization. There was no indication that medication prescriptions are increased after hospitalizations. No significant risk reduction for hospitalizations with injury diagnoses was observed during periods of ADHD medication, but there was a preventive effect on the risk of brain injuries (34% risk reduction). The effects were controlled for time-invariant characteristics of the patients by the study design.

Food Security and Teenage Labor Supply

AbstractThis study assesses whether teenage labor force participation may influence the food security of children in their families. We utilize the Current Population Survey annual Food Security Supplement and linked monthly core data from 2001 through 2012 to assess the year‐to‐year dynamics of food security status in families with teenagers. We estimate the effect of teenage employment on food security while controlling for all time‐invariant individual and household characteristics using a fixed‐effects model. We find that an employed teen reduces the predicted probability of a family's children having very low food security by an economically and statistically significant 50%.

Relationship between recycling rate and air pollution: Waste management in the state of Massachusetts

This study examines the relationship between recycling rate of solid waste and air pollution using data from a waste municipality survey in the state of Massachusetts during the period 2009–2012. Two econometric approaches are applied. The first approach is a fixed effects model, while the second is a Stochastic Frontier Analysis (SFA) with fixed effects model. The advantage of the first approach is the ability of controlling for stable time invariant characteristics of the municipalities, thereby eliminating potentially large sources of bias. The second approach is applied in order to estimate the technical efficiency and rank of each municipality accordingly. The regressions control for various demographic, economic and recycling services, such as income per capita, population density, unemployment, trash services, Pay-as-you-throw (PAYT) program and meteorological data. The findings support that a negative relationship between particulate particles in the air 2.5μm or less in size (PM2.5) and recycling rate is presented. In addition, the pollution is increased with increases on income per capita up to $23,000–$26,000, while after this point income contributes positively on air quality. Finally, based on the efficiency derived by the Stochastic Frontier Analysis (SFA) model, the municipalities which provide both drop off and curbside services for trash, food and yard waste and the PAYT program present better performance regarding the air quality.

A Quantitative Analysis of the Relationship between Medicare Payment and Service Volume for Glaucoma Procedures from 2005 through 2009

To calculate the association between Medicare payment and service volume for 6 commonly performed glaucoma procedures. Retrospective, longitudinal database study. A 100% dataset of all glaucoma procedures performed on Medicare Part B beneficiaries within the United States from 2005 to 2009. Fixed-effects regression model using Medicare Part B carrier data for all 50 states and the District of Columbia, controlling for time-invariant carrier-specific characteristics, national trends in glaucoma service volume, Medicare beneficiary population, number of ophthalmologists, and income per capita. Payment-volume elasticities, defined as the percent change in service volume per 1% change in Medicare payment, for laser trabeculoplasty (Current Procedural Terminology [CPT] code 65855), trabeculectomy without previous surgery (CPT code 66170), trabeculectomy with previous surgery (CPT code 66172), aqueous shunt to reservoir (CPT code 66180), laser iridotomy (CPT code 66761), and scleral reinforcement with graft (CPT code 67255). The payment-volume elasticity was nonsignificant for 4 of 6 procedures studied: laser trabeculoplasty (elasticity, -0.27; 95% confidence interval [CI], -1.31 to 0.77; P = 0.61), trabeculectomy without previous surgery (elasticity, -0.42; 95% CI, -0.85 to 0.01; P = 0.053), trabeculectomy with previous surgery (elasticity, -0.28; 95% CI, -0.83 to 0.28; P = 0.32), and aqueous shunt to reservoir (elasticity, -0.47; 95% CI, -3.32 to 2.37; P = 0.74). Two procedures yielded significant associations between Medicare payment and service volume. For laser iridotomy, the payment-volume elasticity was -1.06 (95% CI, -1.39 to -0.72; P < 0.001): for every 1% decrease in CPT code 66761 payment, laser iridotomy service volume increased by 1.06%. For scleral reinforcement with graft, the payment-volume elasticity was -2.92 (95% CI, -5.72 to -0.12; P = 0.041): for every 1% decrease in CPT code 67255 payment, scleral reinforcement with graft service volume increased by 2.92%. This study calculated the association between Medicare payment and service volume for 6 commonly performed glaucoma procedures and found varying magnitudes of payment-volume elasticities, suggesting that the volume response to changes in Medicare payments, if present, is not uniform across all Medicare procedures.

A Longitudinal Analysis of Violence and Housing Insecurity

Violence and housing insecurity are horrible events that may be intertwined, with violence possibly forcing victims to abandon their accommodations and housing insecurity depriving people of the safety of a home or placing them in compromised circumstances. This study uses national, prospective, longitudinal data from the Journeys Home Survey to examine how violence, housing insecurity, and other characteristics in one period affect disadvantaged Australian men's and women's chances of experiencing violence and housing insecurity in subsequent periods. The study is one of the first to investigate these relationships prospectively and unusual in considering how violence among adult men contributes to their housing insecurity. We estimate dynamic multivariate models that control for observed and time-invariant unobserved characteristics and find that men's chances of being housing secure without experiencing violence are 24-45 percent lower and women's chances are 12- 20 percent lower if they experienced housing insecurity, violence or both in the previous period. Heavy drinking, marijuana use, psychological distress, and a history of childhood abuse and neglect also increase the risks of violence and housing insecurity for both genders, while the presence of children reduces these risks. Women who are bisexual or lesbian and women with homeless friends also face elevated risks of housing insecurity, while men's sexual orientation and friend networks seem less relevant.