Empirical research in the areas of health economics and medical statistics that uses a new econometric method called “partial identification” is making progress. This paper evaluates the applications of partial identification to these areas to see how effective and insightful this new method is. Section 2 presents research on partial identification for missing-data problems. For example, when infection data for COVID-19 are missing for people who have not been tested, the infection rate of the entire population cannot be accurately known. Empirical studies in this area have most commonly assumed that data are missing at random; for this particular example, the assumption would then be that the infection rate of the population at large is the same as that of people who have been tested. In contrast, research using partial identification would first apply the Law of Total Probability to the infection rate of the entire population, next assign the observed probabilities to the infection rate of the tested people and the ratio of the tested people, and finally replace the missing (counterfactual) rate of infection among those who have not been tested with 0 (its lower bound) and 1 (its upper bound) to obtain the identification region (the bound) of the infection rate of then tire population. Furthermore, the identification bounds can be narrowed by imposing credible assumptions, such as “people who are tested tend to have higher infection rates than those who are not tested” (Monotone Instrumental Variable Assumption). In Sections 3 and 4, we explain how to partially identify the causality and treatment effect using as examples(i) the effect of Swan-Ganz catheterization on mortality, and (ii) the effect of antihypertensive drugs conditional on renin response. We first explain the identification problem, i.e., the reason why the treatment effect cannot be point-identified only from the data. We then show that partial identification allows the treatment effect to be identified from the data alone as an interval (the bounds) without any assumption. We next show how the identification bounds on the treatment effect narrow when credible assumptions are imposed (Instrumental Variable Assumption and Monotone Treatment Response Assumption). The more assumptions and the stronger assumptions one imposes, the narrower are the bounds; this yields stronger conclusions, but lower credibility of inference. Thus, we are required to decide what assumptions to maintain. Finally, we consider how a decision maker who knows that the treatment effects are identified in bounds might choose an action using as examples (i) treatment of a new infection disease and (ii) choice of diagnostic testing and treatment. In the present context, the Bayesian criterion would be a good choice only when the subjective expected probability of the treatment effect is correct. The maximin criterion would be a conservative choice (which grants deference to the status quo), while the minimax-regret criterion would be a choice that balances conservatism (in deferring to the status quo) and challenge (in reflecting the innovation).

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In this paper, we investigate how the wage distribution of employees with a mental disability (i.e., impairment caused by a mental illness) has changed in the wake of the sharp increase in the number of these employees after the application of the disability employment obligation to them and the increase in the mandatory employment rate under the revised Act to Facilitate the Employment of Persons with Disabilities. For our analysis, we used two microdata sets, namely, the Disabled Employment Survey (2013, 2018) and the Life Difficulty Survey (2011, 2016), which are conducted by the Ministry of Health, Labour and Welfare. There are three major findings. First, on average, workers with a mental disability, whose disability was recognized by their employers prior to hiring, experienced statistically significant wage increases between2011 and 2018. Second, Blinder-Oaxaca decomposition of wage increases revealed that the regional minimum wage was the main driving factor (compositional factor), and the change in the wage function parameter of persons with the mildest (grade 3) mental disabilities had some positive effects (structural factor). Third, these wage increases of employees with mental disabilities were spoiled by the decrease of the parameter of the wavefunction (structural factor) in large enterprises with more than one thousand employees. The wage increase for employees with the mildest (grade 3) mental disabilities could be explained by the following factors: Between 2013 and 2018, the number of persons newly certified for grade 3 mental disability has increased sharply, especially among the working-age population, compared with more severe mental disability levels. The proportion of employees with grade 3 mental disability has also increased among the total number of employees with disabilities. Furthermore, in the same period, as the population of employees with physical disabilities under the age of 65 years continues to decrease as these workers retire, employers might experience difficulty filling these vacancies to meet the obligatory disability employment rate. Employers would then fill vacancies with workers with the mildest (grade 3) mental disabilities and would expect high productivity relative to hiring other workers with more severe mental disability. This would explain the wage increases for employees with grade 3 mental disabilities. However, compared with employees with physical disabilities, the wage distribution of employees with mental disabilities is much lower and closer to that of employees with intellectual disabilities. Thus, the abovementioned wage increases would not be sufficient to bridge the gap between the low pension benefits (e.g., the grade 3 employees’ disability pension for the mildest disabilities) and the minimum income for people with relatively mild mental disability, as indicated by previous research. The high correlation with regional minimum wages may be an indication that wage levels are quite low. The extent to which these wage increases reduce the risk of poverty for people with mental disabilities remains to be investigated in future studies.

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Against the backdrop of increasing medical costs associated with factors such as the aging population and sophisticated medical technology, interest in medical economics is expanding. In 2019, Japan’s total medical expenses exceeded 44 trillion yen, with drug costs accounting for approximately 20%. Various factors are responsible for the increase in medical expenses, but medical expenses for lifestyle-related diseases are particularly problematic. Therefore, in this study, we investigated the status of metformin use, a drug frequently prescribed as a therapeutic agent for type 2 diabetes, and the current status of its adoption in clinical settings (hospitals). Results showed that use of metformin, based on NDB open data, has been increasing year by year since 2015, and more than 2.2 billion tablets were used in 2020. The adoption of metformin in clinical settings (hospitals) was observed in all facilities surveyed. However, more than 80% of the facilities used only 250 mg/tablet as the standard. Therefore, in cases where the single dose was 500 mg, two 250 mg tablets were dispensed. Metformin is a relatively inexpensive drug; as of April 2022, the price for250 mg/tablet and 500 mg/tablet generic drugs was the same (10.10 yen). Thus, if the single dose is 500 mg, the drug cost is twice as much when dispensed as two 250 mg tablets, compared to that when dispensing one500 mg tablet. Regardless of whether it is adopted in the hospital, in the case of generic drug prescriptions, itis possible to change to the appropriate tablet standard at the discretion of the pharmacist at the insurance dispensing pharmacy, depending on the notation on the outpatient’s prescription. Therefore, the effect of drug dissolution behavior based on single tablets (one 500 mg/tablet) and multiple tablets (two 250 mg/tablet)was evaluated and found to be equivalent, suggesting the possibility of drug cost savings at the pharmacist’s discretion even while continuing current treatments.

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