CORD-19-Sentences  

CORD-19:b1afea22f6b06be09e29b3e5bddc3cc2f7897957 JSONTXT 8 Projects

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Id Subject Object Predicate Lexical cue
TextSentencer_T1 0-78 Sentence denotes Ambient temperature, birth rate, and birth outcomes: evidence from South Korea
TextSentencer_T2 80-88 Sentence denotes Abstract
TextSentencer_T3 89-190 Sentence denotes The effects from rising temperatures, a symptom of climate change, have become a significant concern.
TextSentencer_T4 191-432 Sentence denotes This study finds that one additional day with a maximum temperature of 30-32°C (86-89.6°F), relative to a day with a temperature of 28-30°C (82.4-86°F), decreases the birth rate 9 months later by 0.24%, or 92 babies per month in South Korea.
TextSentencer_T5 433-493 Sentence denotes This result is robust to various specifications and samples.
TextSentencer_T6 494-639 Sentence denotes This study also found that the impact of the temperature bin did not vary according to the mother's characteristics, including education and age.
TextSentencer_T7 640-729 Sentence denotes That is, high temperature has no differential effect on mothers of different backgrounds.
TextSentencer_T8 730-901 Sentence denotes Finally, we found no significant temperature effect on birth outcomes, but we cannot rule out that children born 9 months after summer heat are a selected (healthy) group.
TextSentencer_T9 903-987 Sentence denotes The impact of climate change on human life has become a major issue in recent years.
TextSentencer_T10 988-1086 Sentence denotes The effect of rising temperatures due to greenhouse gas emissions has become even more pronounced.
TextSentencer_T11 1087-1220 Sentence denotes The Intergovernmental Panel on Climate Change (2014) found that, in 2010, global emissions of carbon dioxide were twice that of 1970.
TextSentencer_T12 1221-1346 Sentence denotes Greenhouse gas emissions increase the ambient temperature as they absorb and release radiation in the thermal infrared range.
TextSentencer_T13 1347-1456 Sentence denotes Previous literature has documented the fact that summers have become increasingly hot due to this phenomenon.
TextSentencer_T14 1457-1610 Sentence denotes For example, Habeeb et al. (2015) found that the frequency and intensity of heat waves increased significantly between 1961 and 2010 across 50 US cities.
TextSentencer_T15 1611-1689 Sentence denotes Few studies have analyzed the relationship between temperature and birth rate.
TextSentencer_T16 1690-1825 Sentence denotes Those that have include Seiver (1985 Seiver ( , 1989 , Roenneberg and Aschoff (1990) , Miron (1991, 1996) , and Barreca et al. (2018) .
TextSentencer_T17 1826-1984 Sentence denotes They used relatively old data, 1 and found a negative relationship between temperature and birth rate; that is, high temperatures reduce the number of births.
TextSentencer_T18 1985-2328 Sentence denotes Barreca et al. (2018) , the most recent of the studies, examined data obtained between 1931 and 2010 and found that an additional day with a mean temperature of 80°F or higher decreased birth rates 8, 9, and 10 months later, but increased them 11-23 months later; the net effect of these findings is equal to a decrease in birth rate of 0.33%.
TextSentencer_T19 2329-2493 Sentence denotes The study also found that an additional day with a temperature of 80°F or higher increased the current month's birth rate and decreased that of the following month.
TextSentencer_T20 2494-2565 Sentence denotes 2 , 3 However, they found no significant impact from cold temperatures.
TextSentencer_T21 2566-2674 Sentence denotes Using data from South Korea, this study examines the effect of temperature on birth rate and birth outcomes.
TextSentencer_T22 2675-2725 Sentence denotes It complements the existing literature as follows.
TextSentencer_T23 2726-2808 Sentence denotes First, this study analyzes relatively recent data, obtained between 2009 and 2013.
TextSentencer_T24 2809-3057 Sentence denotes Presenting results based on recent data can be a valuable addition to the literature because populations adapt to extreme weather; thus, a prediction of the effect of future temperature is likely to be more reliable when it is based on recent data.
TextSentencer_T25 3058-3193 Sentence denotes Second, when estimating the temperature effect, this study compares birth rate and birth outcomes within the same city/month over time.
TextSentencer_T26 3194-3323 Sentence denotes This prevents the possibility of bias when comparing different months in the same city or different cities within the same month.
TextSentencer_T27 3324-3364 Sentence denotes Thus, the analysis is a cohort analysis.
TextSentencer_T28 3365-3515 Sentence denotes According to Hsiang (2016) , this is a strengthening of the unit homogeneity assumption because different cohorts within the same unit are comparable.
TextSentencer_T29 3516-3623 Sentence denotes Since the data does not span a long period, the same city/month can be assumed to be homogeneous over time.
TextSentencer_T30 3624-3724 Sentence denotes Third, this study focuses on the influence of summer heat because rising temperatures impact people.
TextSentencer_T31 3725-3960 Sentence denotes Therefore, this study employs daily maximum temperatures rather than the daily average temperatures used in prior studies, because average temperatures may not accurately reflect the extent of the summer heat, as experienced by people.
TextSentencer_T32 3961-3998 Sentence denotes This study's findings are as follows.
TextSentencer_T33 3999-4187 Sentence denotes One additional day with a maximum temperature of 30-32°C, relative to a day with a maximum temperature of 28-30°C, decreases the birth rate 9 months later by 0.24%, or 92 babies per month.
TextSentencer_T34 4188-4248 Sentence denotes This result is robust to various specifications and samples.
TextSentencer_T35 4249-4394 Sentence denotes This study also found that the impact of the temperature bin did not vary according to the mother's characteristics, including education and age.
TextSentencer_T36 4395-4484 Sentence denotes That is, high temperature has no differential effect on mothers of different backgrounds.
TextSentencer_T37 4485-4656 Sentence denotes Finally, we found no significant temperature effect on birth outcomes, but we cannot rule out that children born 9 months after summer heat are a selected (healthy) group.
TextSentencer_T38 4657-4846 Sentence denotes 1 For example, Seiver (1989 ) used data from 1950 to 1960 , while Lam and Miron (1996 ) used data from 1942 to 1988 Temperature has also been found to affect human life spans (Robine et al.
TextSentencer_T39 4847-4925 Sentence denotes 2008; Deschênes and Moretti 2009; Barreca 2012) , economic growth (Dell et al.
TextSentencer_T40 4926-4994 Sentence denotes 2012) , time use (Graff Zivin and Neidell 2014), crime (Jacob et al.
TextSentencer_T41 4995-5061 Sentence denotes 2007; Ranson 2014) , and test scores (Cho 2017; Graff Zivin et al.
TextSentencer_T42 5062-5069 Sentence denotes 2018) .
TextSentencer_T43 5070-5108 Sentence denotes See Dell et al. (2014) for the review.
TextSentencer_T44 5109-5283 Sentence denotes 3 Studies on other weather conditions affecting birth rates include Huber and Fieder (2009) and Cummings (2010) , who examined the effects of rain and sunshine, respectively.
TextSentencer_T45 5284-5336 Sentence denotes The remainder of this paper is organized as follows.
TextSentencer_T46 5337-5526 Sentence denotes The next section reviews the literature, followed by presentation of the data; the "Empirical strategy" section outlines the empirical strategy, which is followed by the estimation results.
TextSentencer_T47 5527-5587 Sentence denotes The "Discussion and conclusion" section concludes the paper.
TextSentencer_T48 5588-5715 Sentence denotes High temperatures can lead to reduced number of pregnancies due to increased fatigue and heat-related diseases (McMorris et al.
TextSentencer_T49 5716-5732 Sentence denotes 2006; Bai et al.
TextSentencer_T50 5733-5750 Sentence denotes 2014; Nybo et al.
TextSentencer_T51 5751-5818 Sentence denotes 2014) , reduced sexual desire (Markey and Markey 2013; Wilde et al.
TextSentencer_T52 5819-5887 Sentence denotes 2017) , deterioration of female reproductive health (Sorensen et al.
TextSentencer_T53 5888-5948 Sentence denotes 2018) , and decreased sperm count and quality (Levine et al.
TextSentencer_T54 5949-5966 Sentence denotes 1990; Chen et al.
TextSentencer_T55 5967-5987 Sentence denotes 2003; Levitas et al.
TextSentencer_T56 5988-6004 Sentence denotes 2013; Mao et al.
TextSentencer_T57 6005-6012 Sentence denotes 2017) .
TextSentencer_T58 6013-6137 Sentence denotes Avoidance or lack of pregnancy because of hot weather decreases the number of newborns 9 months after a heat exposure event.
TextSentencer_T59 6138-6292 Sentence denotes 4 Resuming efforts to become pregnant immediately thereafter increases the number of newborns 10 months after the heat exposure event (delayed pregnancy).
TextSentencer_T60 6293-6390 Sentence denotes If the pregnancy period is shortened, the number of newborns in the expected month will decrease.
TextSentencer_T61 6391-6531 Sentence denotes For example, if the pregnancy period is shortened by 1 month, babies that were expected to be born 1 month later will be born in this month.
TextSentencer_T62 6532-6644 Sentence denotes In this case, this month will see an increase in the number of newborns, and the next month will see a decrease.
TextSentencer_T63 6645-6727 Sentence denotes 5 Studies on the effect of temperature on birth outcomes have shown mixed results.
TextSentencer_T64 6728-6812 Sentence denotes Some studies found that high temperatures cause a low birth weight (Deschênes et al.
TextSentencer_T65 6813-6833 Sentence denotes 2009; Andalón et al.
TextSentencer_T66 6834-6854 Sentence denotes 2016; Barreca et al.
TextSentencer_T67 6855-6896 Sentence denotes 2018 ) and preterm births (Dadvand et al.
TextSentencer_T68 6897-6916 Sentence denotes 2011; Strand et al.
TextSentencer_T69 6917-6937 Sentence denotes 2011; Barreca et al.
TextSentencer_T70 6938-7033 Sentence denotes 2018) , possibly because, at high temperatures, blood flow to the uterus decreases (Basu et al.
TextSentencer_T71 7034-7114 Sentence denotes 2010 ) and the body secretes stress hormones, such as cortisol (Yackerson et al.
TextSentencer_T72 7115-7122 Sentence denotes 2008) .
TextSentencer_T73 7123-7206 Sentence denotes However, other studies found no significant effect on birth outcomes (Porter et al.
TextSentencer_T74 7207-7226 Sentence denotes 1999; Tustin et al.
TextSentencer_T75 7227-7243 Sentence denotes 2004; Lee et al.
TextSentencer_T76 7244-7251 Sentence denotes 2008) .
TextSentencer_T77 7252-7253 Sentence denotes 6
TextSentencer_T78 7254-7458 Sentence denotes This study analyzes birth and population data from the National Statistical Office for the period of 2009 to 2013 and weather data from Korean Meteorological Administration for the period of 2008 to 2013.
TextSentencer_T79 7459-7679 Sentence denotes The birth data are based on registrations of newborns in all 162 cities in the country, which include information on the birth year/month, gender, birth weight, gestational length, and parental ages and education levels.
TextSentencer_T80 7680-7918 Sentence denotes 7 The total number of newborns for the 5-year period is 2.3 million, and for each year, it is 444,849 (2009), 470,171 (2010), 471,265 (2011), 484,550 (2012) , and 4 The term "9 months" in this paper refers to 36-40 weeks into a pregnancy.
TextSentencer_T81 7919-8013 Sentence denotes 5 Lam et al. (1994) presented a fertility model incorporating coital frequency and fetal loss.
TextSentencer_T82 8014-8154 Sentence denotes 6 Studies examining the effects of temperature in utero on other outcomes include Isen et al. (2015) and Wilde et al. (2017) , respectively.
TextSentencer_T83 8155-8310 Sentence denotes Studies analyzing other shocks to the in utero environment include Almond et al. (2009) , Black et al. (2013) , Sanders (2012) , and Hoynes et al. (2016) .
TextSentencer_T84 8311-8442 Sentence denotes For earlier studies on the relationship between the in utero environment and birth or later outcomes, see Almond and Currie (2011).
TextSentencer_T85 8443-8528 Sentence denotes 7 The government requires parents to register their newborns within a month of birth.
TextSentencer_T86 8529-8571 Sentence denotes 436,455 (2013) with an average of 461,458.
TextSentencer_T87 8572-8640 Sentence denotes The yearly average for the 162 cities is 2848 and the median is 669.
TextSentencer_T88 8641-8726 Sentence denotes The population data include information on the number of residents in each city/year.
TextSentencer_T89 8727-8870 Sentence denotes The data are based on local registrations, and the number of residents is the average resident numbers on the first and last days of each year.
TextSentencer_T90 8871-8973 Sentence denotes The weather data include information on daily maximum temperature and precipitation at the city level.
TextSentencer_T91 8974-9123 Sentence denotes All are taken from actual weather stations, but in the case of the seven cities around Seoul without stations, Seoul's weather data are used instead.
TextSentencer_T92 9124-9236 Sentence denotes 8 , 9 Table 1 shows the number of days per month with a daily maximum temperature in the given range for cities.
TextSentencer_T93 9237-9456 Sentence denotes For example, for ≥ 32°C, a city in the bottom 25th percentile has 1.2 days per month, or 14.4 days (= 1.2 × 12) per year, and a city in the top 25th percentile has 2.2 days per month, or 26.4 days (= 2.2 × 12) per year.
TextSentencer_T94 9457-9504 Sentence denotes The table also shows the number for each month.
TextSentencer_T95 9505-9629 Sentence denotes For example, August, the hottest month, has an average of 10.9 days of temperatures ≥ 32°C, followed by July, with 5.2 days.
TextSentencer_T96 9630-9713 Sentence denotes Table 2 presents data (at the city/year-month level) on newborns and their mothers.
TextSentencer_T97 9714-9842 Sentence denotes The daily birth rate is 2.24, which means over the 5 years, an average of 2.24 children per 100,000 residents was born each day.
TextSentencer_T98 9843-10012 Sentence denotes The rate is defined as the number of newborns in a month divided by the number of days in the month, divided by the city/year population, and then multiplied by 100,000.
TextSentencer_T99 10013-10115 Sentence denotes In addition, the proportions of girls and babies of low birth weight are 48.5% and 5.2%, respectively.
TextSentencer_T100 10116-10183 Sentence denotes Consider birth rate regression Eq. (1) for city c and year/month t.
TextSentencer_T101 10184-10259 Sentence denotes The subscripts m and y represent the calendar month and year, respectively.
TextSentencer_T102 10260-10356 Sentence denotes The dependent variable is the natural log of birth rate, which is defined in the "Data" section.
TextSentencer_T103 10357-10534 Sentence denotes Temp is a variable representing the daily maximum temperature of each month and consists of the following six categories: < 22°C, 22-24°C, 24-26°C, 26-28°C, 30-32°C, and ≥ 32°C.
TextSentencer_T104 10535-10629 Sentence denotes Using categorical variables for temperature is now standard across the literature (Dell et al.
TextSentencer_T105 10630-10637 Sentence denotes 2014) .
TextSentencer_T106 10638-10771 Sentence denotes For example, ≥ 32°C indicates the number of days in a month for which the daily maximum temperature is equal to or greater than 32°C.
TextSentencer_T107 10772-10854 Sentence denotes The superscript 6 of the Temp variable represents ≥ 32°C, and 1 represents < 22°C.
TextSentencer_T108 10855-10941 Sentence denotes The bin of 28-30°C is excluded from the equation and is used as a comparison category.
TextSentencer_T109 10942-11200 Sentence denotes 10 If no bin is excluded, the coefficients for each temperature bin indicate the value of the dependent variable, and, therefore, one should compare the coefficients to examine how a temperature bin affects the birth rate relative to another temperature bin.
TextSentencer_T110 11201-11242 Sentence denotes Excluding a bin exempts us from doing so.
TextSentencer_T111 11243-11365 Sentence denotes This study includes the temperature of the current month and past temperatures from up to 12 months prior in the equation.
TextSentencer_T112 11366-11497 Sentence denotes If, for example, Temp 6 ct-9 has a value of 3, then city c experienced 3 days of maximum temperature of ≥ 32°C 9 months previously.
TextSentencer_T113 11498-11764 Sentence denotes In addition, Rain is a variable representing the total precipitation of each month and consists of the following three categories: < The number for each city is calculated by dividing the number of days for each bin in a city in a year by 60 (= 12 months × 5 years).
TextSentencer_T114 11765-11907 Sentence denotes The number for the month is calculated by dividing the weighted sum of days for each bin in a city in a month by 810 (= 162 cities × 5 years).
TextSentencer_T115 11908-11960 Sentence denotes City/year populations are used as the weight Source:
TextSentencer_T116 11961-12069 Sentence denotes The author's own calculation based on the weather and population data Mother-no college degree (%) 39.1 11.9
TextSentencer_T117 12070-12091 Sentence denotes Mother's age 30.9 1.0
TextSentencer_T118 12092-12129 Sentence denotes Mother-35 years or older (%) 16.6 6.9
TextSentencer_T119 12130-12153 Sentence denotes Teen mother (%) 1.0 1.9
TextSentencer_T120 12154-12174 Sentence denotes Number of cities 162
TextSentencer_T121 12175-12205 Sentence denotes Number of city/year-month 9718
TextSentencer_T122 12206-12368 Sentence denotes Birth rate is defined as the number of newborns in a month divided by the number of days in the month, divided by the city/year population, multiplied by 100,000.
TextSentencer_T123 12369-12452 Sentence denotes Thus, the birth rate is the average daily number of newborns per 100,000 residents.
TextSentencer_T124 12453-12583 Sentence denotes Low birth weight means weighing less than 2500 g at birth, and preterm birth means being born before 37 weeks OF pregnancy Source:
TextSentencer_T125 12584-12692 Sentence denotes The author's own calculation based on the birth registry and population data 34 mm, 72-150 mm, and ≥ 150 mm.
TextSentencer_T126 12693-12830 Sentence denotes 11 The bin of 34-72 mm is excluded from the equation, and the equation includes the rainfall of the current month and the past 12 months.
TextSentencer_T127 12831-12915 Sentence denotes This variable is included because it is known to affect health outcomes (Dell et al.
TextSentencer_T128 12916-12923 Sentence denotes 2014 ).
TextSentencer_T129 12924-13014 Sentence denotes The vector X includes the mothers' average age and education at the city/year-month level.
TextSentencer_T130 13015-13077 Sentence denotes Education is the proportion of mothers with no college degree.
TextSentencer_T131 13078-13186 Sentence denotes These variables are included because the mother's characteristics are likely to affect the number of births.
TextSentencer_T132 13187-13417 Sentence denotes Although the maximum temperature in a city on a given day is determined randomly, following Barreca et al. (2018) , this study includes a variety of fixed effects in the regression to address the confounding of unobserved factors.
TextSentencer_T133 13418-13538 Sentence denotes In the equation, η is the city/month fixed effect, and thus the birth rate of the same city/month is compared over time.
TextSentencer_T134 13539-13665 Sentence denotes That is to say, the January birth rate of a city in a year is compared with the January birth rate of the city in other years.
TextSentencer_T135 13666-13882 Sentence denotes Without this variable, it is difficult to know whether the differences in birth rates are due to variations in temperature or variations in characteristics of the month or of cities. γ is the year/month fixed effect.
TextSentencer_T136 13883-13970 Sentence denotes This variable controls for factors affecting the whole country in a certain year/month.
TextSentencer_T137 13971-14132 Sentence denotes For example, avoiding pregnancy when suspecting, say, a Middle East respiratory syndrome coronavirus infection will reduce the number of newborns 9 months later.
TextSentencer_T138 14133-14272 Sentence denotes If we do not control for this variable, we cannot tell whether the low number of newborns can be attributed to the virus or to the weather.
TextSentencer_T139 14273-14318 Sentence denotes In addition, δ is the city/year fixed effect.
TextSentencer_T140 14319-14384 Sentence denotes This variable controls for factors affecting a certain city/year.
TextSentencer_T141 14385-14550 Sentence denotes For example, if a city experiences an economic recession in 2012, leading residents to postpone marriage and childbirth, the number of newborns will decline in 2013.
TextSentencer_T142 14551-14608 Sentence denotes The city/year fixed effects can control for such factors.
TextSentencer_T143 14609-14738 Sentence denotes Finally, ν c × t and ν c × t 2 are the interactions between city fixed effects and time trend variables t and t 2 , respectively.
TextSentencer_T144 14739-14794 Sentence denotes Equation (1) is estimated using ordinary least squares.
TextSentencer_T145 14795-14878 Sentence denotes The regression includes 9718 (= 162 cities × 5 years × 12 months − 2) observations.
TextSentencer_T146 14879-15024 Sentence denotes Two city/year-months are excluded from the analysis because the number of newborns is zero in those cases and it is not possible to take the log.
TextSentencer_T147 15025-15097 Sentence denotes The coefficients of interest are the coefficients for the Temp variable.
TextSentencer_T148 15098-15283 Sentence denotes Although Eq. (1) includes a variety of fixed effects to control for unobserved factors, the estimates could be biased if there are factors affecting both temperature and the birth rate.
TextSentencer_T149 15284-15379 Sentence denotes One possible factor is air pollution, which may cause global warming and affect the birth rate.
TextSentencer_T150 15380-15460 Sentence denotes However, a temperature rise due to air pollution occurs gradually, not abruptly.
TextSentencer_T151 15461-15613 Sentence denotes That is, air pollution occurring in a certain month is not likely to affect temperature in the near future and thus is not likely to bias the estimates.
TextSentencer_T152 15614-15778 Sentence denotes Even if this were the case, one of the fixed effects can control for air pollution, as long as it affects the entire country (or city) in a certain year (or month).
TextSentencer_T153 15779-15980 Sentence denotes It is noteworthy that the estimates include the impact of avoidance behaviors (e.g., staying indoors or using air conditioning) because people engage in such behaviors in response to high temperatures.
TextSentencer_T154 15981-16050 Sentence denotes Hence, the interpretation of the result should reflect this behavior.
TextSentencer_T155 16051-16150 Sentence denotes That is, the estimates reflect both the effect of the temperature and the effect of such behaviors.
TextSentencer_T156 16151-16299 Sentence denotes Finally, this study also analyzes the impact of temperature on birth outcomes, including the probability of a low birth weight and of preterm birth.
TextSentencer_T157 16300-16464 Sentence denotes For the former, the dependent variable is the proportion of babies with low birth weight, and the independent variables are the same as those in regression Eq. (1).
TextSentencer_T158 16465-16575 Sentence denotes When estimating the impact on birth outcomes, the number of newborns in each city/month is used as the weight.
TextSentencer_T159 16576-16673 Sentence denotes The effect of temperature on birth rate Table 3 shows the result of the regression using Eq. (1).
TextSentencer_T160 16674-16761 Sentence denotes Each column of the table presents the temperature effect 0-12 months after summer heat.
TextSentencer_T161 16762-16905 Sentence denotes In addition, multiplying the dependent variable by 100, a coefficient of, say, − 0.3, can be interpreted as a 0.3% reduction in the birth rate.
TextSentencer_T162 16906-17093 Sentence denotes According to the table, an additional day with a maximum temperature of 30-32°C, relative to a day with a maximum temperature of 28-30°C, decreases the birth rate 9 months later by 0.24%.
TextSentencer_T163 17094-17301 Sentence denotes This result is consistent with the findings of Barreca et al. (2018) , who showed that in the 2000s, an additional day with a mean temperature of 80°F or higher reduced the birth rate 9 months later by 0.2%.
TextSentencer_T164 17302-17580 Sentence denotes The effect size of 0.24% found in this study is equivalent to 92 fewer babies per month in the entire country because an annual average of 461,458, or a monthly average of 38,455 (= 461,458/12), was born in the country during the 5 years, and 0.24% of the monthly average is 92.
TextSentencer_T165 17581-17712 Sentence denotes The reduced birth rate 9 months after an incidence of high temperature means there were reduced pregnancies due to the hot weather.
TextSentencer_T166 17713-17857 Sentence denotes In addition, the lack of evidence of a change in the birth rate in other months, as shown in Table 3 , means there was no shift in birth months.
TextSentencer_T167 17858-17947 Sentence denotes That is, we found no evidence of any shortening of pregnancy length or delayed pregnancy.
TextSentencer_T168 17948-18169 Sentence denotes 12 In Table 3 , although no coefficients for the maximum temperature of ≥ 32°C are statistically significant, some of them are fairly large in absolute value, implying that we cannot rule out large impacts in some months.
TextSentencer_T169 18170-18259 Sentence denotes 13 Finally, we also estimated the average temperature effect, as in the previous studies.
TextSentencer_T170 18260-18403 Sentence denotes The temperature bins are ≥ 25°C, 20-25°C, 10-15°C, 5-10°C, 0-5°C, < 0°C, and the bin of 15-20°C is omitted to be used as a comparison category.
TextSentencer_T171 18404-18464 Sentence denotes As Table 4 shows no estimates are statistically significant.
TextSentencer_T172 18465-18539 Sentence denotes As a robustness check, we control for humidity in the regression equation.
TextSentencer_T173 18540-18618 Sentence denotes The analysis is limited to 81 cities because not every city has humidity data.
TextSentencer_T174 18619-18782 Sentence denotes When we limit the analysis to 81 cities without controlling for humidity, the birth rate 9 months after the daily maximum temperature of 30-32°C reduces by 0.237%.
TextSentencer_T175 18783-18846 Sentence denotes When we control for it, the result remains unchanged at 0.245%.
TextSentencer_T176 18847-18896 Sentence denotes Other coefficients also do not show a difference.
TextSentencer_T177 18897-18979 Sentence denotes This implies that humidity does not affect the temperature-fertility relationship.
TextSentencer_T178 18980-19058 Sentence denotes We also estimated the temperature effect by adding bins of lower temperatures.
TextSentencer_T179 19059-19133 Sentence denotes The following temperature bins were added to the original ones in Eq. (1):
TextSentencer_T180 19134-19172 Sentence denotes 19-22°C, 16-19°C, …, 1-4°C, and < 1°C.
TextSentencer_T181 19173-19212 Sentence denotes Again, the bin of 28-30°C was excluded.
TextSentencer_T182 19213-19282 Sentence denotes Table 5 shows that the result is not different from that in Table 3 .
TextSentencer_T183 19283-19549 Sentence denotes That is, an additional day with Table 3 The effects of maximum temperature relative to 28-30°C on the log birth rate (× 100) Dependent variable = log of birth rate Months after the weather event Standard errors are in parentheses and are clustered at the city level.
TextSentencer_T184 19550-19683 Sentence denotes Multiplying the dependent variable by 100, a coefficient of, say, − 0.3, can be interpreted as a reduction in the birth rate of 0.3%.
TextSentencer_T185 19684-20007 Sentence denotes The regression also includes a constant, the mothers' average age, the proportion of mothers with no college degree, the three dummy variables for the amount of total rainfall, city/month fixed effect, year/month fixed effect, city/year fixed effect, and the two interactions between the city fixed effects and time trends.
TextSentencer_T186 20008-20339 Sentence denotes The preceding year's population is used as the weight *Statistically significant at the 5% level Table 4 The effects of average temperature relative to 15-20°C on the log birth rate (× 100) Dependent variable = log of birth rate Months after the weather event Standard errors are in parentheses and are clustered at the city level.
TextSentencer_T187 20340-20451 Sentence denotes The dependent variable is multiplied by 100, and other independent variables are the same as those in Table 3 .
TextSentencer_T188 20452-20646 Sentence denotes The preceding year's population is used as the weight a maximum temperature of 30-32°C, relative to a day with a maximum temperature of 28-30°C, decreases the birth rate 9 months later by 0.23%.
TextSentencer_T189 20647-20817 Sentence denotes For the third robustness check, we estimated the temperature effect using past temperatures from up to 20 months prior and found that this also did not change the result.
TextSentencer_T190 20818-20879 Sentence denotes As shown in Table 6 , the coefficient for 30-32°C is − 0.291.
TextSentencer_T191 20880-21011 Sentence denotes For the last robustness test, to determine whether a particular city drives the result in Table 3 , we excluded one city at a time.
TextSentencer_T192 21012-21146 Sentence denotes The choice of cities was made from the largest seven cities in the country, which have higher birth rates than the average birth rate.
TextSentencer_T193 21147-21229 Sentence denotes They are Seoul, the capital city, along with Daejeon, Gwangju, Incheon, and Ulsan.
TextSentencer_T194 21230-21303 Sentence denotes 14 As shown in Table 7 , the exclusion leaves the coefficients unchanged.
TextSentencer_T195 21304-21380 Sentence denotes For example, when Seoul is excluded, the coefficient for 30-32°C is − 0.237.
TextSentencer_T196 21381-21443 Sentence denotes Who is affected and how are they affected by high temperature?
TextSentencer_T197 21444-21524 Sentence denotes Table 3 shows that high temperature reduces the number of births 9 months later.
TextSentencer_T198 21525-21690 Sentence denotes To investigate who is affected by the high temperature, this section estimates the temperature's effect on the mothers' characteristics, including education and age.
TextSentencer_T199 21691-21868 Sentence denotes Less educated and older or teen mothers could be affected more by a high temperature, possibly because they may have less knowledge about heat avoidance and may be less healthy.
TextSentencer_T200 21869-21953 Sentence denotes That is, the reduced births shown in Table 3 could be due to these types of mothers.
TextSentencer_T201 21954-22324 Sentence denotes The dependent variables of the analyses in Table 8 are the percentages of mothers with no Table 5 The effects of maximum temperature relative to 28-30°C on the log birth rate (× 100) 9 months after the weather event using the full distribution of temperatures Dependent variable = log of birth rate Standard errors are in parentheses and are clustered at the city level.
TextSentencer_T202 22325-22436 Sentence denotes The dependent variable is multiplied by 100, and other independent variables are the same as those in Table 3 .
TextSentencer_T203 22437-22532 Sentence denotes The preceding year's population is used as the weight 14 Figure 1 shows the map of the country.
TextSentencer_T204 22533-22642 Sentence denotes The country is divided into the seven largest cities and nine provinces, including Gyunggi surrounding Seoul.
TextSentencer_T205 22643-22690 Sentence denotes The other two large cities are Busan and Daegu.
TextSentencer_T206 22691-22957 Sentence denotes The effects of maximum temperature relative to 28-30°C on the log birth rate (× 100) using past temperatures up to 20 months Dependent variable = log of birth rate Months after the weather event Standard errors are in parentheses and are clustered at the city level.
TextSentencer_T207 22958-23069 Sentence denotes The dependent variable is multiplied by 100, and other independent variables are the same as those in Table 3 .
TextSentencer_T208 23070-23232 Sentence denotes The preceding year's population is used as the weight *Statistically significant at the 5% level college degree, of mothers aged 35 or older, and of teen mothers.
TextSentencer_T209 23233-23321 Sentence denotes In addition, the estimates in the table are the effect 9 months after the weather event.
TextSentencer_T210 23322-23407 Sentence denotes The table shows that a high temperature does not affect the mothers' characteristics.
TextSentencer_T211 23408-23575 Sentence denotes While the coefficients for 30-32°C in columns (1) and (3) are negative, they are not significant, and the positive coefficient in column (2) is not significant either.
TextSentencer_T212 23576-23659 Sentence denotes When the weather is hot, the number of births may reduce for the following reasons.
TextSentencer_T213 23660-23804 Sentence denotes As described in the "Literature review" section, people may reduce coital frequency, possibly due to heat-related fatigue (a behavioral factor).
TextSentencer_T214 23805-24003 Sentence denotes Even if the frequency is not reduced, the probability of conception may decline as a result of decreased sperm count and/or quality and deteriorated female reproductive health (a biological factor).
TextSentencer_T215 24004-24244 Sentence denotes Although this study cannot examine how each factor explains the temperature effect due to a lack of data, the reduced number of pregnancies 9 months after summer heat, as found in Table 3 , can be reasonably attributed to these two factors.
TextSentencer_T216 24245-24307 Sentence denotes This study estimates the temperature effect on birth outcomes.
TextSentencer_T217 24308-24471 Sentence denotes As the "Literature review" section describes, high temperatures may cause low birth weight and preterm births, although some studies did not find evidence of this.
TextSentencer_T218 24472-24543 Sentence denotes Table 9 shows the results, with each panel representing one regression.
TextSentencer_T219 24544-24641 Sentence denotes As shown in the two panels of the table, no estimates in the table are statistically significant.
TextSentencer_T220 24642-25029 Sentence denotes Although no estimates in Table 9 are statistically significant, it cannot be concluded that summer heat does not cause unhealthy babies because, considering that babies not conceived because of summer heat would have been born with worse birth outcomes if they had been conceived and born, the estimates of this study could underestimate the true effect of temperature on birth outcomes.
TextSentencer_T221 25030-25097 Sentence denotes That is, the estimates in Table 9 are possibly biased by selection.
TextSentencer_T222 25098-25169 Sentence denotes Standard errors are in parentheses and are clustered at the city level.
TextSentencer_T223 25170-25281 Sentence denotes The dependent variable is multiplied by 100, and other independent variables are the same as those in Table 3 .
TextSentencer_T224 25282-25335 Sentence denotes The preceding year's population is used as the weight
TextSentencer_T225 25336-25461 Sentence denotes This study estimated the effect of temperature on birth rates and birth outcomes for newborns in Korea between 2009 and 2013.
TextSentencer_T226 25462-25673 Sentence denotes The results showed that an additional day with a maximum temperature of 30-32°C, relative to a day with a maximum temperature of 28-30°C, decreased the birth rate 9 months later by 0.24%, or 92 babies per month.
TextSentencer_T227 25674-25778 Sentence denotes This study also found high temperatures have no differential effect on mothers of different backgrounds.
TextSentencer_T228 25779-25890 Sentence denotes The effects on the birth rate found in this study are smaller than the effects found in Barreca et al. (2018) .
TextSentencer_T229 25891-26043 Sentence denotes The difference may arise because the present study examines relatively recent data, while Barreca et al. (2018) analyze data obtained from 1931 to 2010.
TextSentencer_T230 26044-26146 Sentence denotes That is to say, people in modern times may respond differently to summer heat than people in the past.
TextSentencer_T231 26147-26308 Sentence denotes The former may use air conditioning more frequently than the latter and might be more accustomed to summer heat because they experience hot days more frequently.
TextSentencer_T232 26309-26392 Sentence denotes In fact, Barreca et al. (2018) found that the effect size declined after the 1960s.
TextSentencer_T233 26393-26546 Sentence denotes One additional factor that may make a difference in the two studies is that the mothers included in this study have a relatively high level of education.
TextSentencer_T234 26547-26656 Sentence denotes As shown in Table 2 , mothers with no college degree account only for 39%, and the rest have a higher degree.
TextSentencer_T235 26657-26842 Sentence denotes Assuming that highly educated people have more knowledge about heat avoidance and more resources to follow through on this knowledge, this study should find smaller temperature effects.
TextSentencer_T236 26843-26977 Sentence denotes Korea has a fertility rate lower than any other industrialized country, which could lead to severe labor shortages in the near future.
TextSentencer_T237 26978-27127 Sentence denotes 15 Though high temperatures have been found to have the potential to reduce the rate further, people can 15 The total fertility rate is 1.05 in 2017.
TextSentencer_T238 27128-27212 Sentence denotes This data can be downloaded at the following website of National Statistical Office.
TextSentencer_T239 27213-27360 Sentence denotes http://kosis.kr/statHtml/statHtml.do?orgId=101&tblId=DT_1B8000F&language=en Standard errors are in parentheses and are clustered at the city level.
TextSentencer_T240 27361-27423 Sentence denotes Other independent variables are the same as those in Table 3 .
TextSentencer_T241 27424-27652 Sentence denotes The number of newborns is used as the weight Table 9 The effects of maximum temperature relative to 28-30°C on birth outcomes Months after the weather event Standard errors are in parentheses and are clustered at the city level.
TextSentencer_T242 27653-27715 Sentence denotes Other independent variables are the same as those in Table 3 .
TextSentencer_T243 27716-27893 Sentence denotes The number of newborns is used as the weight *Statistically significant at the 5% level effectively minimize the temperature and economic impact through heat avoidance behavior.
TextSentencer_T244 27894-28086 Sentence denotes Although this study does not examine the temperature-birth rate relationship based on this behavior, future studies should analyze how heat avoidance behavior mitigates the temperature effect.