
collection‘ from Anqing data set, which  indicates that respondents across the two cities,  in general, 
are concerned about the improvement  of attribute  levels and a relatively reasonable experimental 
design  we  have.  The  model  fit  of  model  2  for  each  data  set  is  improved  by  incorporating  the 
interaction terms. Model  2 is highly consistent with model 1  in terms  of signs and significance of 
attribute coefficients. It reveals that assuming other factors remain constant, improving the levels of 
‗waste classification‘, ‗frequency of waste collection‘ and ‗frequency of waste transportation‘ would 
increase respondents‘  utility  while  increasing  the  fee would  decrease  their  utility.  But  respondents 
from different data sets have different preferences for attributes, e.g., respondents in Nanchang tend 
to  focus  on  ‗waste  classification‘  and  ‗frequency  of  waste  transportation‘  while  respondents  in 
Anqing  are  inclined  to  ‗frequency  of  waste collection‘.  It  should  be  noted  that the coefficient on 
‗frequency of waste collection‘ has the largest value but is not significantly different from zero at the 
10% level in Anqing data set, and its accuracy and reliability  deserve the following  further study. 
The interaction terms have different signs and significance across the two data sets. Model 2 for 
Nanchang  manifests  respondents  who  have  higher  household  income,  more  environmental 
knowledge, higher awareness of environmental protection, or more positive subjective perception of 
the  environmental  behaviors  of  their  neighbors  are  willing  to  pay  more  for  improving  MSWM 
services,  ceteris  paribus.  As  to  Anqing  data  set,  education,  household  income,  environmental 
awareness, and subjective perception of the environmental behaviors of neighbors have significantly 
improved households‘ willingness to contribute money. These findings are consistent with previous 
studies  [20,  21,  31,  32].  However,  older  people  in  Anqing  are  more  reluctant  to  pay,  which  is 
intuitively  correct  since  older  people  have  low  level  of  environmental  awareness  and  are  more 
conservative in spending in China. 
Despite  widely  used,  MNL  model  has  severe  limitations  with  respect  to  the  well-known 
assumption  of  independence  of  irrelevant  alternatives  and  its  ability  to  capture  random  taste 
heterogeneity across individuals [33, 34]. Hence, we will move to apply a less restrictive and more 
flexible model to the following  analysis. 
3.2.2. The results of random parameter logit (RPL) model. As RPL model tends to be unstable and 
identification  issues arise when all coefficients vary over the population,  the coefficient on fee  is 
fixed while other coefficients are allowed to vary in our analysis (see Goett et al., Revelt and Train) 
[35, 36]. Considering some respondents may be satisfied with the status quo, e.g., respondents need 
not have to spend time and energy on waste separation nor have to pay extra money, we specify the 
coefficients  on  ‗waste  classification‘,  ‗frequency  of  waste  collection‘  and  ‗frequency  of  waste 
transportation‘  to  be  normally  distributed.  Attributes  showing  insignificant  standard  deviation  are 
then respecified as nonrandom parameters. At last, ‗frequency of waste collection‘ and ‗frequency of 
waste  transportation‘  are  specified  as  random  parameters and  other  variables  remain  nonrandom 
parameters  in  estimation  models  for  the  two  data  sets.  To  identify  the  potential  sources  of 
heterogeneity,  random  parameters  are  interacted  with  socio-economic  and  attitudinal  variables. 
Initially,  all  possible  interactions  are  put  into  estimation  model  for  each  city  and  finally  only 
interactions that are significant at the 10% level or less are retained. The estimation results are shown 
in Table 5. 
The estimation of RPL model results  in considerable improvement of model fit over the MNL 
model. All parameter estimates related to the attributes and ASC are statistically significant and have 
the expected signs including the ‗frequency  of waste  collection‘  for  Anqing  data set,  on which  the 
coefficient is  insignificant in the  MNL  model.  The  ASC  and  ‗waste classification‘  are  nonrandom 
parameters for the two cities, implying that respondents generally agree to improve the services of 
MSWM at the expense of extra spending and waste separation, which is out of our expectation. One 
possible explanation  is that,  along with the  increasing negative impacts of waste on residents and 
Estimating Willingness to Pay for Improving Municipal Solid Waste Management Using a Choice Experiment: A Case Study of Central
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