Using discrete choice modeling to evaluate the preferences and willingness to pay for leptospirosis vaccine

Figures & data

Table 1. Socio-demographic characteristics of the 2 case respondents

		Leptospirosis case Respondents	Non-Leptospirosis case Respondents
		n=114	n=228	Difference
		[1]	[2]	[1]-[2]
Variable	Description	Average (S.D)	Average (S.D)	(│t│-Ratio)
AGE	Age of the respondent in years	34.90 (13.64)	37.93 (12.59)	−3.03** (1.99)
EDUCATION	Years of education	9.97 (2.41)	10.28 (2.02)	−0.31* (1.18)
FAMILYSIZE	Number of persons in a household	5.17 (2.02)	5.08 (1.98)	0.09 (0.39)
INCOME	Household income (‘000 pesos/month)	16.95 (11.96)	18.90 (11.64)	−1.95 (1.43)
MALE	Dummy: 1 = male respondent; 0 = female	0.90 (0.30)	0.60 (0.50)	0.31*** (7.20)
MARKET	Dummy: 1 if home is located near to a market (about 10 m);0 if far	0.83 (0.37)	0.72 (0.45)	0.11** (2.39)
RIVER	Dummy: 1 if home is located near to a river (about 10 m);0 if far	0.62 (0.49)	0.64 (0.48)	−0.02 (0.31)
SEWER	Dummy: 1 if home is located near to a sewer (about 10 m);0 if far	0.75 (0.44)	0.65 (0.48)	0.10 (1.79)
AWARENESS	Leptospirosis awareness score	0.93 (0.18)	0.83 (0.23)	0.10*** (4.25)

Note: ***denotes statistical significance at 1% level and **5% significance level.

Table 2. Results of the Random Parameters Logit (RPL) model estimation

	Model 1: Leptospirosis case Respondents		Model 2: Non-leptospirosis case Respondents		Model 3: Pooled data set
Variables	Coeff.	Std. Err.	Coeff.	Std. Err.	Coeff.	Std. Err.
Random parameters of vaccine attributes in the model
EFFICACY of 50–60%^a	−2.842***	0.318	−2.157***	0.193	−2.270***	0.154
EFFICACY of 70–80%	0.607***	0.126	0.442***	0.079	0.479***	0.057
EFFICACY of 90–100%	2.235***	0.256	1.715***	0.142	1.791***	0.127
PROTECTION of 2 years^a	−0.521***	0.318	−0.531***	0.077	−0.500***	0.063
PROTECTION of 7 years	0.108***	0.118	0.242***	0.065	0.144***	0.054
PROTECTION of 10 years	0.413***	0.116	0.289***	0.064	0.356***	0.054
SERIOUS RISK of side effects^a	−0.963***	0.130	−0.401***	0.075	−0.559***	0.062
MODERATE RISK of side effects	0.337***	0.121	0.159***	0.066	0.195***	0.052
MILD RISK of side effects	0.626***	0.129	0.242***	0.066	0.364***	0.055
Given in 3 SHOTS^a	−0.580***	0.154	−0.506***	0.129	−0.453***	0.097
Given in 2 SHOTS	0.068***	0.296	0.164***	0.190	0.077***	0.149
Given in 1 SHOT	0.512***	0.188	0.342***	0.109	0.376***	0.087
Non-random main effects parameters of vaccine attributes in the model
Alternative Specific Constant	2.424***	0.994	0.255	0.476	0.317	0.395
Price	−3.167***	0.403	−3.548***	0.251	−3.291***	0.172
Socio-demographics & Alternative Specific Constant (ASC) interaction in the model ^b
AGE*ASC	−0.002	0.008	−0.010***	0.004	−0.007	0.004
EDUCATION*ASC	−0.067	0.046	0.058***	0.028	0.121	0.022
FAMILYSIZE*ASC	−0.082	0.520	−0.060***	0.028	−0.042	0.024
INCOME*ASC	0.015	0.011	0.012***	0.012	0.010***	0.004
MALE*ASC	0.121	0.422	0.200	0.199	0.527***	0.103
Living near to a MARKET*ASC	0.265	0.281	0.063	0.063	0.148	0.109
Living near to a RIVER*ASC	−0.063	0.233	0.419***	0.119	0.219***	0.102
Living near to a SEWER*ASC	−0.975***	0.282	−0.232***	0.118	−0.314***	0.107
Leptospirosis AWARENESS*ASC	1.216***	0.568	0.680***	0.235	1.040***	0.209
Derived Standard deviations of the parameter distributions
EFFICACY of 70–80%	0.105	9.473	0.041	3.854	0.012	0.167
EFFICACY of 90–100%	1.114***	0.301	0.331	0.597	0.517	0.619
PROTECTION of 7years	0.070	2.414	0.004	5.776	0.006	0.168
PROTECTION of 10 years	0.027	4.160	0.374	0.441	0.764	0.236
MODERATE RISK of side effects	1.080***	0.353	0.010	1.158	0.338***	0.251
MILD RISK of side effects	0.071	2.372	0.004	4.007	0.060	0.167
Given in 2 SHOTS	0.443	1.407	0.009	4.906	0.011***	0.232
Given in 1 SHOT	0.209	1.384	0.968	0.198	0.703***	0.209
Log-likelihood	−865.776		−2035.251		−2968.334
McFadden R^2	0.424		0.323		0.342
No of parameters	27		27		27
χ^2 statistics	1274.252***		1941.104***		3080.741***
No of observation	1368		2736		4104

Notes: ***denotes statistical significance at 1% level and **5% significance level. ^aBase attribute level. Its coefficient was derived as the negative sum of the coefficients of the other 2 alternative attribute levels. ^bThe interaction terms indicate which respondents’ characteristics affect the likelihood of accepting the leptospirosis vaccination program.

Table 3. Estimates of implicit prices for each of the non-monetary attributes of the leptospirosis vaccine by case respondents

		Leptospirosis Case Respondents	Non-Leptospirosis Case Respondents	Difference
Vaccine Attribute		[1]	[2]	[1]–[2]
Base Level	Improved Level	Implicit price^a (95% C.I)	Implicit price^a (95% C.I)	(│t│-Ratio)
EFFICACY of 50–60%	EFFICACY of 70–80%	1,089.04***	732.53***	356.52***
		(850.49∼1,327.60)	(611.99∼853.06)	(26.34)
	EFFICACY of 90–100%	1,603.09***	1,091.32***	511.78***
		(1,259.07∼1,947.12)	(939.29∼1,243.34)	(32.16)
PROTECTION of 2 years	PROTECTION of 7 years	198.61	217.87***	−19.25
		(332.23∼65.00)	(153.69∼282.05)	(1.92)
	PROTECTION of 10 years	294.92***	231.09***	63.83***
		(161.38∼428.45)	(166.16∼296.01 )	(6.34)
SERIOUS RISK of side-effects	MODERATE RISK of side-effects	410.48***	157.84**	252.65***
		(276.72∼544.24)	(93.26∼222.42)	(25.12)
	MILD RISK of side-effects	501.74***	181.23***	320.51***
		(366.73∼636.74)	(117.65∼244.81)	(31.84)
Given in 3 SHOTS	Given in 2 SHOTS	204.61	188.84	15.77
		(499.56∼−90.34)	(359.75∼17.93)	(1.02)
	Given in 1 SHOT	344.81***	239.01***	105.80***
		(184.41∼505.20)	(159.89∼318.12)	(9.57)

Notes: ***denotes statistical significance at 1% level and **5% significance; ^aIn pesos (1 peso = US$ 0.024 based on October 2012 exchange rate).

Table 4. Estimates of respondents’ willingness to pay (WTP) for combined attributes of leptospirosis vaccine

	Leptospirosis Case Respondents	Non-Leptospirosis Case Respondents	Difference
	[1]	[2]	[1]–[2]
Vaccine Attribute Combinations	WTP in pesos^a	WTP in pesos^a
	(95% C.I.)	(95% C.I.)	(│t│-Ratio)
Scenario 1:
EFFICACY of 70–80%	1,903.88	1,297.39	606.49***
PROTECTION of 7 years	(1,413.35∼2,394.41)	(1,057.35∼1,537.43)	(31.41)
MODERATE RISK of side-effects
Given in 2 SHOTS
Scenario 2:
EFFICACY of 90–100%	2,745.62	1,743.19	1,002.43***
PROTECATION of 10 years	(2,174∼3,316.43)	(1,504.74∼1,981.64)	(49.33)
MILD RISK of side-effects
Given in 1 SHOT

***denotes statistical significance at 1%; ^a1 peso = US$ 0.024 based on October 2012 exchange rate.