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Table 5 Logit specifications on WTP responses

From: Impact of environmental and social attitudes, and family concerns on willingness to pay for improved air quality: a contingent valuation application in Mexico City

Explanatory variables Entire Excluding highest category Excluding Excluding
sample Income (I) Age (II) (I) and (II) protest responses
Bid −0.0024*** -0.0024*** −0.0024*** −0.0023*** −0.0019***
(2008 US $) (0.0003) (0.0003) (0.0003) (0.0003) (0.0003)
Environmental and social attitudes 
 Air pollution problem is very important (1 if yes; 0 otherwise) 1.1512 (0.2560)*** 1.0818 (0.2495)*** 1.1728 (0.2575)*** 1.0987 (0.2510)*** 0.5677 (0.2787)**
 Poverty/economic development problem is very important (1 if yes; 0 otherwise) −1.1317 (0.4669)* −1.1207 (0.4657)* −0.9308 (0.4561)* −0.9203 (0.4538)* −1.2010 (0.4642)*
 Both air pollution and poverty problems are very important (1 if yes; 0 otherwise) 1.3957 (0.5054)** 1.4635 (0.5044)** 1.1676 (0.4937)* 1.2383 (0.4921)* 1.4261 (0.5088)***
Family concerns
 Family member sick of respiratory illness or allergy (1 if yes; 0 otherwise) 0.9372 (0.2477)*** 0.7538 (0.2462)** 0.8998 (0.2499)*** 0.7130 (0.2483)** 0.9495 (0.2695)***
 Car at household (1 if yes; 0 otherwise) 0.4188 (0.2282) 0.5274 (0.2291)* 0.4392 (0.2277) 0.5504 (0.2285)* 0.7003 (0.262)***
 More adults at household than sample median (i.e. 2) −1.3614 (0.2236)*** −1.1820 (0.2260)*** −1.3782 (0.2240)*** −1.1939 (0.2261)*** −1.6214 (0.2381)***
 More children at household than sample median (i.e. 1) -0.331 (0.2359) -0.3832 (0.2327) −0.2826 (0.2350) −0.3358 (0.2315) −0.3456 (0.2596)
Socioeconomic controls
 Male (1 if yes; 0 otherwise) −0.1644 (0.1956) −0.0957 (0.1925) −0.1403 (0.1962) −0.0703 (0.1932) −0.7388 (0.2129)***
Job status
 Part-time job -0.1352 (0.2568) -0.1198 (0.2508) -0.1096 (0.2561) -0.0934 (0.2500) 0.3854 (0.2779)
 Full-time job 1.0362 (0.3469)** 1.0279 (0.3422)** 1.0359 (0.3387)** 1.0267 (0.3335)** 1.6952 (0.3601)***
Range of respondent’s age 
 25–35 0.1011 (0.2473) 0.0565 (0.2427) 0.0948 (0.2465) 0.0479 (0.2418) −0.7256 (0.3741)*
 35–45 0.1669 (0.3424) 0.1354 (0.3406) 0.1105 (0.3379) 0.0796 (0.3361) −0.6871 (0.4609)
 45–55 0.9327 (0.4093)* 0.8463 (0.4080)* 0.8960 (0.4098)* 0.8067 (0.4088)* 0.0520 (0.4937)
 >55 3.2530 (0.6821)*** 3.2256 (0.6799)*** 2.7303 (0.7448)***
Monthly household income (2008 US$)
 US $567–US $967 0.8850 (0.2529)*** 0.7802 (0.2463)** 0.8993 (0.2514)*** 0.7925 (0.2449)** 1.6086 (0.3336)***
 US $967–US $2167 1.5738 (0.4308)*** 1.4101 (0.4227)*** 1.5547 (0.422)*** 1.3889 (0.4132)*** 1.5789 (0.4247)***
 US $2167–US $5000 -2.0399 (0.5151)*** −1.9532 (0.5096)*** −1.9479 (0.5360)***
Respondent’s contribution to monthly household income
 50–75% 1.1867 (0.3164)*** 1.2078 (0.3140)*** 1.1626 (0.3153)*** 1.1854 (0.3133)*** 0.8187 (0.3083)**
 >75% 2.9332 (0.8069)*** 2.9175 (0.8030)*** 2.7959 (0.7570)*** 2.7815 (0.7530)*** 2.3957 (0.6467)***
Interactions between household income and respondent’s contribution
Income Contribution  
US $567–US $967 50–75% −1.5199 (0.5830)** −1.4693 (0.5669)** −1.1988 (0.6195) −1.1557 (0.6016) −2.0715 (0.6044)***
Interactions between household income and respondent’s contribution
Income Contribution  
US $567–US $967 >75% −1.783 (1.0377) −1.7074 (1.0304) –1.7075 (1.0030) −1.6251 (0.9954) −1.8820 (0.9415)*
US $967–US $2167 50–75% −2.7109 (0.5566)*** −2.6308 (0.5483)*** −2.7178 (0.5544)*** −2.6349 (0.5453)*** −2.2579 (0.5569)
US $967–US $2167 >75% −2.3054 (1.1840) −2.2085 (1.1680) −2.1273 (1.1453) −2.0363 (1.1294) -1.7597* (1.1023)
 Intercept 0.9889 (0.3649)** 0.9174 (0.3568)* 0.9130 (0.3576)* 0.8441 (0.3500)* 1.7013*** (0.4430)
 n 1541 1490 1243 1192 1499
 Pseudo-R2 0.3527 0.3487 0.2989 0.2925 0.3582
 Log-likelihood −434.7521 −421.9019 −428.6136 −415.6528 -379.1291
  1. Standard errors in parenthesis. Coefficients are significant at *** 99%, ** 95%, or * 90% level of confidence
  2. aReference category: no job
  3. bReference category: 18-25
  4. cReference category: <US$ 567
  5. dReference category: <50%
  6. eNot all interactions are included because of missing cells in the corresponding excluded interaction