Heckman Sample Selection Model Research Articles

Using instruments for selection to adjust for selection bias in Mendelian randomization.

Selection bias is a common concern in epidemiologic studies. In the literature, selection bias is often viewed as a missing data problem. Popular approaches to adjust for bias due to missing data, such as inverse probability weighting, rely on the assumption that data are missing at random and can yield biased results if this assumption is violated. In observational studies with outcome data missing not at random, Heckman's sample selection model can be used to adjust for bias due to missing data. In this paper, we review Heckman's method and a similar approach proposed by Tchetgen Tchetgen and Wirth (2017). We then discuss how to apply these methods to Mendelian randomization analyses using individual-level data, with missing data for either the exposure or outcome or both. We explore whether genetic variants associated with participation can be used as instruments for selection. We then describe how to obtain missingness-adjusted Wald ratio, two-stage least squares and inverse variance weighted estimates. The two methods are evaluated and compared in simulations, with results suggesting that they can both mitigate selection bias but may yield parameter estimates with large standard errors in some settings. In an illustrative real-data application, we investigate the effects of body mass index on smoking using data from the Avon Longitudinal Study of Parents and Children.

The effects of social capital and family income on farmers’ participation in rural public goods provision

Farmers' participation in rural public goods provision (PGP) is vital to improving rural public goods conditions and achieving rural revitalization in China. The factors influencing farmers' participation are, however, far from clear. This paper aims to investigate how social capital and income, the two most prominent factors, affect rural residents' participation in PGP. We use the Heckman sample selection model to empirically estimate the effects of both social capital and family income on farmers' participation and contribution to PGP based on a household survey conducted in four representative provinces in China. We further investigate the moderating effect of village location and elite ability on the effect of social capital on farmers' participation. Our results show that social capital generally has a positive impact on farmers' participation. Specifically, improving the formal norm, size of networks, and density of network would increase farmers' participation propensity. Enriching norms, particularly formal norms, can significantly improve farmers' contribution to public goods. Surprisingly, family income, mainly non-farm income, has a slightly negative effect on farmers' participation. Moreover, village-county distance can undermine the effect of social norms on farmers' participation, while elite ability can enhance the effect of social trust on farmers' participation. Thus, we suggest authorities should focus on enhancing social capital in the rural community to promote farmers’ participation in PGP.

Consumers´ willingness to pay for snacks enriched with insects: A trending and sustainable protein source

High-protein snacks appeal to consumers seeking to increase the protein intake in their diet. The high environmental impact of conventional protein sources is urging the need to explore more sustainable alternatives such as edible insects. In this study, the willingness to pay for yogurt enriched with insect protein was estimated. It also determined the effect of socio-demographics and extrinsic product attributes on the purchase decision and expenditure using the Heckman sample selection model. Data was collected through an online survey from 1,909 consumers in Catalonia, Spain using Qualtrics´ consumer panel. The results showed that 55.7% of the participants were willing to purchase the product and that the average premium price computed was 0.36€ or 24% extra compared to the conventional price of yogurt. Findings also revealed that the probability of purchasing yogurt enriched with insect protein increases with younger adults, male consumers, residing in rural areas, having a child member in the family unit, and an active employment situation. Moreover, expenditure increases when the importance of the local and ecological attributes of food is higher, while lower for the price attribute. The results of this study offer food producers valuable insights into consumers’ willingness to pay for novel protein snacks.

The Effect of Family Members’ Perceived Upward Mobility on Marriage and Childbirth Using Heckman Sample Selection Model

The Effect of Family Members’ Perceived Upward Mobility on Marriage and Childbirth Using Heckman Sample Selection Model

Members’ willingness to pay for sustainability agricultural organization: A Heckman model approach

The purpose of this research analyzed the factors influencing the members’ willingness to pay capital in the agricultural cooperatives and unions. The research was performed on a sample 155 members of agricultural organizations in Igdir province of Türkiye using the Simple Random Sampling method. Members’ willingness to pay capital to their organizations were examined using the Contingent Valuation Method and effected factors were analyzed by Heckman Sample Selection model. The research showed that 56.6% of members were willing to pay capital an average of $131 for sustainability of organizations. According to the model results showed that members’ gender, agricultural income, know definition of organization, increase in income of members, pay entry capital, frequency of visiting, meeting the general assembly, cohesion of members positively affected, however, age, household, animal units, negative experience in the past with their organizations negatively affected the members’ willingness to pay capital. In order to sustainable of agricultural organizations, cohesion of members and participation to general assembly must increase. And, encouraging more young and female farmers to become a member, taking an active role cooperatives and unions in marketing and supply input could increase the members’ willingness to pay capital. In addition, training programs should be organized by agricultural organizations and government about increasing capital and economic participation.
 Keywords: Agricultural organizations; Contingent analysis; Cooperative; Heckman sample selection model; Willingness to pay capital

Public Agricultural Extension, Pest and Disease Experience, and Adoption of Improved Wheat Varieties

Improved varieties are considered critical for increasing crop yields worldwide. This study explored the effects of public agricultural extension and pest and disease experience on adoption of improved varieties using survey data on 525 wheat farmers in Anhui Province, China, to which the Heckman sample selection model was applied. The results showed that public agricultural extension had a significant positive relationship with adoption of improved varieties. Demonstration and training, as different forms of agricultural extension, both increased the probability of farmers adopting improved varieties, but only demonstration had a marked effect on degree of adoption. Pest and disease experience increased the probability of adoption of improved varieties by farmers and significantly enhanced the effect of public agricultural extension, but did not affect degree of adoption. Further analysis using an endogenous switching regression model revealed that adoption of improved varieties raised wheat yields by around 337.83 kg/ha. Public agricultural extension should thus be strengthened, especially for farmers with pest and disease experience, and a diversified, well-functioning agricultural extension system should be provided.

표본 선택 모형을 통한 밀레니얼 세대의 인턴십 경험이 취업 및 임금에 미치는 영향 분석

The aim of this study is to analyze the influence of internship experiences on the employment and wages of millennials during their college years to understand the actual labor market outcomes of internships. For this purpose, we utilized data from the 2020 Graduate Occupational Mobility Survey (GOMS 2019) to estimate a probit model and a wage equation using Heckman two-stage model. First, the model validity analysis confirms that the Heckman's sample selection model is statistically significant for this study, exhibiting a negative correlation, with smaller wages having a higher probability of being selected into the sample. Second, the first-stage of Heckman’s probit model analyzed the effects of internship experiences on employment, revealing that internships positively impact employment prospects. This impact was statistically significant with regard to gender, academic grade, metropolitan region, and the father's level of education. Third, in Heckman's two-stage wage equation estimation, it was found that internship experience did not influence wages, wherein the study showed that regular employees earned approximately 22% more than non-regular employees.

The determinants of household electricity demand in Turkey: An implementation of the Heckman Sample Selection model

Residential areas have a significant share in electrical energy consumption in Turkey. At this point, determining electricity consumption demand in residential areas will significantly contribute to ensuring energy efficiency throughout the country. Accurate econometric modelling of the relationships between the various socio-economic characteristics of households and their energy consumption/expenditure can serve as a basis for policymakers when planning investments aimed at efficiency on primary energy consumption in residences. Considering these issues, this study aims to examine the electricity consumption demand in residential areas in Turkey in terms of various socio-economic and building and property characteristics variables. At this point, the fact that some households have zero electricity consumption has led to the need to use censored regression models. The Heckman Sample Selection model was used, which makes it possible to estimate the consumption decision of individuals in two stages and eliminates the parameter bias problem caused by linear regression analysis. Heckman Sample Selection modelling was carried out in the study using Turkish Statistical Institute (TURKSTAT) 2019 Household Budget Survey data. According to the results, it has been determined that annual disposable income, various demographic variables (age, education level, marital status), characteristics of the house (size) and the presence of various electrical household appliances (air conditioner, tumble dryer, deep freezer) have significant effects on electricity consumption. The systematic preparation of informative brochures on the effective use of household electrical appliances can significantly contribute to efficiency. In addition, in countries like Turkey that depend on foreign energy, providing incentives towards renewable energy sources is considered necessary to contribute to the country's economy positively.

Sustainable Use of Soil and Water Conservation Technologies and Its Determinants: The Case of the Handosha Watershed, Omo-Gibe River Basin, Ethiopia

For the past forty years, Ethiopia has been promoting sustainable land management activities to enhance agricultural productivity. This study was intended to identify the factors determining farmers’ adoption and continued use of soil bund measures in the Handosha watershed, Omo-Gibe river basin. A multistage sampling technique was used to select 340 households using the Heckman sample selection model. A total of 235 (69.12%) households adopted soil bunds, but only 89 (37.87%) of them were sustainably practicing soil bunds on their farm plots. Most adopters widely practiced soil bunds (49.42%), followed by stone bund (15.9%), and Fanyajuu (10%). The empirical results of the Heckman sample selection model showed that the farming experience, land tenure security, and perception of profitability of conservation measures were significantly positively affected the adoption of soil bund. Whereas, farm plot size and participation in off farm activities significantly negatively influenced the adoption of soil bund. Sustainable use of soil bund measures were significantly positively influenced by land tenure security, family size, and frequency of extension contact, whereas the distance between farm plots and home, and farm plot size were negatively affected. As a result, a design of agro-ecological-based soil and water conservation (SWC) measures was essential in reducing farmland vulnerability to soil erosion and food insecurity. It has been concluded that conservation practices should not only focus on the implementation and biophysical factors but also consider the socioeconomic interests of the farmers to improve the sustainable use of conservation technologies.

The effects of environmental information disclosure on stock price synchronicity in China

Environmental information disclosure has attracted the attention of the capital market because it can convey corporate characteristic information. But there needs to be direct evidence that environmental information disclosure can improve the market's overall efficiency. This study examines whether corporate environmental information disclosure can improve the information efficiency of the capital market. This study takes Chinese listed companies from 2008 to 2021 as samples, constructs a panel fixed effect model, and adopts multiple linear, instrumental variable method and Heckman sample selection model. We find that the disclosure of environmental information in the Chinese market reduces the information efficiency of the capital market represented by the synchronicity of stock prices. The reason is that the information after greenwashing by enterprises needs to be of better quality and more obscure, which disrupts market information. Environmental information disclosure by enterprises prone to greenwashing significantly affects stock price synchronicity, such as low institutional ownership, non-state-owned, growth, and manufacturing firms. Finally, this paper discusses the impact mechanism and confirms that stock liquidity and analyst coverage are the two paths through which environmental information disclosure impacts stock price synchronicity. This study is significant in encouraging the government to strengthen market supervision, promoting enterprises to disclose high-quality environmental information, and improving the pricing efficiency of the capital market.

DS-HECK: double-lasso estimation of Heckman selection model

We extend the Heckman (1979) sample selection model by allowing for a large number of controls that are selected using lasso under a sparsity scenario. The standard lasso estimation is known to under-select causing an omitted variable bias in addition to the sample selection bias. We outline the required adjustments needed to restore consistency of lasso-based estimation and inference for vector-valued parameters of interest in such models. The adjustments include double lasso for both the selection equation and main equation and a correction of the variance matrix. We also connect the estimator with results on redundancy of moment conditions. We demonstrate the effect of the adjustments using simulations and we investigate the determinants of female labor market participation and earnings in the US using the new approach. The paper comes with dsheckman, a dedicated Stata command for estimating double-selection Heckman models.

Study on the Impact of Social Capital on Farmers’ Decision-Making Behavior of Adopting Trusteeship Services

The development of sustainable agriculture is an important link in promoting agricultural modernization. As a new sustainable agricultural production model, the promotion effect of agricultural production trust depends on the participation of farmers. Therefore, based on the micro-data of 461 valid questionnaires from farmers in the Heilongjiang Province and the Heckman sample selection model, this study empirically analyzed the impact of social capital on the decision behavior of farmers to adopt custody services from two aspects of adoption behavior and adoption degree. The results showed that social capital had a significant positive impact on the adoption behavior and the degree of adoption of rural households’ trusteeship services. From the perspective of different business scales, for large-scale households, participation in the service promotion activities of agricultural means of production suppliers and trust in the technical information disseminated by the government had a significant positive impact on the adoption of custody services. However, for small farmers, participating in village collective service promotion activities and trusting the service information spread by their neighbors’ relatives and friends had a significant positive impact on trust adoption behavior. Therefore, more attention should be paid to the impact of social capital on farmers’ trust adoption behavior decision making in the future agricultural trust service promotion process to accelerate the promotion of sustainable agricultural development.

Food security through crop diversification in Manipur: Application of Heckman Sample Selection Model

The paper demonstrates the household food security of crop diversified farm in the state of Manipur. A study was conducted at College of Post Graduate Studies in Agricultural Sciences at Barapani, Meghalaya of Central Agricultural University, Imphal during 2015–16 to 2017–18 by taking two districts namely; Ukhrul and Thoubal selecting one from each region, viz. hill and valley of the state, respectively. A sample of 200 households was drawn by using probability proportional to size. Heckman Sample Selection model was used to analyze the data. The study found that most of the households diversified their crop enterprises which in turn enhanced their household food security by way of consuming own production or generated income helped to purchase food items. Among the factors, namely socio-economic, technological and institutional factors influenced household's decision to diversify crop in the state while determinants of dietary diversity were the age of the household head, family size, extent of crop diversification, non-farm source of income and agricultural income. Hence, the results were indicative of the importance of crop diversification as a viable option in the state for enhanced food security and income of rural smallholders. Hence, wider awareness on crop diversification for realizing its benefits and improving the nutritional status of households in the state of Manipur was the need of the hour.

A Generalized Heckman Model With Varying Sample Selection Bias and Dispersion Parameters

Many proposals have emerged as alternatives to the Heckman selection model, mainly to address the non-robustness of its normal assumption. The 2001 Medical Expenditure Panel Survey data is often used to illustrate this non-robustness of the Heckman model. In this paper, we propose a generalization of the Heckman sample selection model by allowing the sample selection bias and dispersion parameters to depend on covariates. We show that the non-robustness of the Heckman model may be due to the assumption of the constant sample selection bias parameter rather than the normality assumption. Our proposed methodology allows us to understand which covariates are important to explain the sample selection bias phenomenon rather than to only form conclusions about its presence. We explore the inferential aspects of the maximum likelihood estimators (MLEs) for our proposed generalized Heckman model. More specifically, we show that this model satisfies some regularity conditions such that it ensures consistency and asymptotic normality of the MLEs. Proper score residuals for sample selection models are provided, and model adequacy is addressed. Simulated results are presented to check the finite-sample behavior of the estimators and to verify the consequences of not considering varying sample selection bias and dispersion parameters. We show that the normal assumption for analyzing medical expenditure data is suitable and that the conclusions drawn using our approach are coherent with findings from prior literature. Moreover, we identify which covariates are relevant to explain the presence of sample selection bias in this important dataset.

Farmers' adoption behavior of conservation tillage technology: a multidimensional heterogeneity perspective.

Adopting conservation tillage technology can promote sustainable agriculture development. There have been many studies on all farmers' conservation tillage behaviors, but few studies are based on a farmer's multidimensional heterogeneity perspective. Given the background, we conduct an empirical evaluation using micro survey data from 819 households in the middle and upper reaches of the Yellow River Basin. This paper uses the entropy method to classify farm households into three types: economically dominant, resource dominant, and socially dominant. Furthermore, we use the Heckman sample selection model to discuss the factors that affect the adoption of conservation tillage technology by different types of farmers. The results show that land fragmentation degree can inhibit economically dominant farmers conservation tillage technology adoption behavior. Social relations can positively influence resource dominant farmers. The share of non-farm income will positively impact socially dominant farmers. This paper further proposes policy implications, based on the findings that different types of farmers have various factors influencing conservation tillage technology adoption behavior.

Should I stay or should I go? The impact of nature reserves on the survival and growth of dairy farms

Special Areas of Conservation (SAC) are part of the EU's nature protection network Natura 2000. SAC often protect nitrogen-sensitive flora and fauna. This is challenging for livestock farmers because they have to meet strict requirements for emission reduction and need to implement costly environmental protection measures. Therefore, SAC could limit farmers' chances to grow or even to survive. This article aims to determine the effects of SAC on dairy farmers by using a Heckman sample selection model. The model explores i) the factors that are relevant to the decision to maintain the farm's existing structure, increase dairy production, exit dairy, or exit agriculture altogether, ii) an OLS regression to analyse the factors that determine the amount of growth in dairy numbers. The analysis was performed for two periods and is based on annual financial statements and regional data such as information about SAC locations. In the first step, the results confirmed the initial hypothesis, finding that farms in districts with more land under nature conservation had a smaller probability of growth. For one of the two periods analysed, higher probabilities of exiting dairy were observed. The second part of the analysis showed that the amount of growth was not affected by SAC protection. The results indicate that SAC protection is indeed challenging for dairy farmers. Further research on the topic is necessary as the area under protection will increase. Since the protected species also depend on (extensive) farming practices, it might be necessary to provide development prospects to farmers that better align with biodiversity objectives.

Use of social health insurance for hospital care by internal migrants in China-Evidence from the 2018 China migrants dynamic survey.

China's welfare system including social health insurance has been closely linked to its unique household registration system, despite high population mobility over the past few decades. This study aimed to determine the pattern of health insurance usage from internal migrants in mainland China for hospital care. Data were extracted from the 2018 China Migrants Dynamic Survey. The respondents who enrolled in a social health insurance program and reported illness or injury over the past year were eligible for this study (n = 15,302). Two groups of outcome indicators were calculated assessing the use (incidence and settlement location) of insurance funds for hospital care and the burden of hospital expenditure (total hospital expenditure, out-of-pocket payments, and share of insurance reimbursement), respectively. Logit regression and Heckman's sample selection models were established to determine the predictors of insurance fund usage and the burden of hospital expenditure, respectively. Most respondents enrolled in a social health insurance program outside of their residential location (70.72%). About 28.90% were admitted to a hospital over the past year. Of those hospitalized, 72.98% were admitted to a hospital at their migration destination, and 69.96% obtained reimbursement from health insurance, covering on average 47% of total hospital expenditure. Those who had a local insurance fund aligned with residency (AOR = 2.642, 95% CI = 2.108-3.310, p < 0.001) and enrolled in employment-based insurance (AOR = 1.761, 95% CI = 1.348-2.301, p < 0.001) were more likely to use insurance funds for hospital care, and paid less out-of-pocket (β = -0.183 for local funds, p = 0.017; β = -0.171 for employment-based insurance, p = 0.005) than others. A higher share of insurance reimbursement as a proportion of hospital expenditure was found in the employment-based insurance enrollees (β = 0.147, p < 0.001). Insurance claim settlement at the residential location was associated with lower total hospital expenditure (β = -0.126, p = 0.012) and out-of-pocket payments (β = -0.262, p < 0.001), and higher share of insurance reimbursement (β = 0.066, p < 0.001) for hospital expenditure. Low levels of health insurance benefits for hospital care are evident for internal migrants in mainland China, which are associated with the funding arrangements linked to household registration and inequality across different funds.

Interaction effects of socioeconomic factors on long-distance commuting after disentangling residential self-selection: An empirical study in Xiamen, China

The adjustment of urban spatial structure in the process of urbanization and suburbanization leads to the separation of work and residence, which further leads to long-distance commuting. While there has been a lot of research on long-distance commuting in Western countries, the relevant studies in China are not enough. In the Chinese context, some factors deserve special attention, namely the hukou system and occupation. However, few studies have focused on the individual and interaction effects of these two factors on long-distance commuting. This paper explores the commuting behavior of different socioeconomic groups in Xiamen, China. Heckman's sample selection model was applied to data from the 2015 Xiamen household travel survey to separate the effect of socioeconomic factors and that of residential selection. Results show that the continued suburbanization of the industry attracted substantial numbers of blue-collar workers to live in the outer districts (Haicang, Jimei, Tong'an, and Xiang'an), and thus blue-collar workers are less likely than pink- and white-collar workers to be long-distance commuters in the outer districts. Among residents of the outer district, pink-collar migrants and white-collar migrants are more likely to be long-distance commuters than their local counterparts, while blue-collar migrants (a coefficient of −0.153) are less likely to be long-distance commuters than blue-collar locals (a coefficient of −0.046). For people who live in the inner districts, blue-collar locals (a coefficient of 0.256) are more likely to be long-distance commuters than blue-collar migrants (a coefficient of −0.029). These results have practical significance for providing alternative housing for migrants in urban renewal.

Factors Affecting Household Expenditures on Education: A Heckman Sample Selection Application for Turkey

Education is undoubtedly one of the most important elements for the development levels of countries and societies. It is also one of the essential requirements in today's world. Education is a key element of an individual’s initial and later social development, therefore development across countries. Today, in most developed countries, the state spends a large amount of fund for education. Households, as well as governments, spend a lot on education. In this study, the expenses for the education of households in Turkey were discussed, and the effect of socio-demographic and economic factors on these expenditures was examined. For this purpose, the data set obtained from the 2019 Household Budget Survey published by the Turkish Statistical Institute (TURKSTAT) was analyzed with the Heckman sample selection model. According to the analysis results, the fact that the head of the household is male in a family, his age, and being married had a negative effect on education expenditures. Education expenses were positively affected by household income, population, the number of technological devices, and the employment of the head of the family. In addition, the structure of the household, the presence of individuals who smoke, go to the cinema, and do sports also affected household education expenditures.

Financial Exclusion and Poverty Reduction in Benin

By analyzing some factors related to the various constraints faced by unbanked individuals, this study explores the determinants associated with individuals without access to common financial services in Benin. It also examines the impact of the lack of access to financial services on poverty using the World Bank’s Global Findex database for 2011, 2014, and 2017. Using a probit model, we found a positive and significant relationship between financial exclusion and lack of documentation, expensive financial services, distance from financial institutions, and lack of trust in financial institutions. Moreover, individual characteristics, such as age, education level, religion, gender, and employment status are significantly associated with financial exclusion. Using a Heckman sample selection model, we show that financial exclusion in Benin has a positive and significant effect on poverty. These results are vindicated using propensity score matching (PSM) for robustness checks.