Hello,
As I understand, the coefficient and standard error of a price variable in a willingness to pay space are generally not reported in peer-reviewed articles. I receive them, however, when I run the following command-
mixlogitwtp Farmer_Choice Opt_Out_Constant, rand(soil_high_c soil_low_c labhc lablc str_hc str_lc leg_hc) price(maize) group(Group_ID) id(HHID)
Please see the results below, where the price variable is reported.
The price variable, maize, assumes either 50, 75, 100 or 125 which correspond to a 50% reduction in current yield, a 25% reduction in current yield, no reduction or a 25% increase in current yield, respectively.
I have three questions based on these results.
Note-
The data includes participants' choices of one agricultural practice out of 2 alternatives or an opt-out option. Thus, participants decide between 3 choices for each hypothetical scenario. Each scenario entails an agricultural practice that includes 5 attributes with 3 levels (excluding the monetary attribute). The choice attributes you see in the table are in effects form and are defined as-
Attribute 1 - soil_high_c/soil_low_c indicate high or low soil fertility received from practice
Attribute 2 - labhc/lablc indicate high or low labor requirements demanded by practice
Attribute 3 - str_hc/str_lc indicate high or low Striga prevalence (a weed that parasitizes maize) received from practice
Attribute 4 - leg_hc/leg_lc indicate high or low legume yield received from practice
Attribute 5 - The monetary attribute is maize.
Status-quo is omitted from each attribute. So soil_med_c, labmc, str_mc and leg_mc are not foud in the mixlogitwtp command.
As I understand, the coefficient and standard error of a price variable in a willingness to pay space are generally not reported in peer-reviewed articles. I receive them, however, when I run the following command-
mixlogitwtp Farmer_Choice Opt_Out_Constant, rand(soil_high_c soil_low_c labhc lablc str_hc str_lc leg_hc) price(maize) group(Group_ID) id(HHID)
Please see the results below, where the price variable is reported.
| Mixed logit model in WTP space Number of obs = 3,870 | ||||||
| Wald chi2(9) = 3223.51 | ||||||
| Log likelihood = -1224.3234 Prob > chi2 = 0.0000 | ||||||
| Coef. | Std. Err. | z | P>z | [95% Conf. | Interval] | |
| Mean | ||||||
| Opt_Out | -1.175352 | 14.05364 | -0.08 | 0.933 | -28.71998 | 26.36928 |
| soil_high_c | 15.00154 | 4.433559 | 3.38 | 0.001 | 6.311928 | 23.69116 |
| soil_low_c | -12.97617 | 5.111912 | -2.54 | 0.011 | -22.99533 | -2.957004 |
| labhc | -14.11424 | 5.324205 | -2.65 | 0.008 | -24.54949 | -3.678993 |
| lablc | 10.83061 | 5.406536 | 2 | 0.045 | 0.2339967 | 21.42723 |
| str_hc | -20.69909 | 5.10284 | -4.06 | 0 | -30.70047 | -10.69771 |
| str_lc | 12.29053 | 5.171295 | 2.38 | 0.017 | 2.154977 | 22.42608 |
| leg_hc | 33.96455 | 6.416826 | 5.29 | 0 | 21.38781 | 46.5413 |
| maize | -4.515235 | 0.1440789 | -31.34 | 0 | -4.797624 | -4.232845 |
| SD | ||||||
| soil_high_c | -1.016615 | 7.598444 | -0.13 | 0.894 | -15.90929 | 13.87606 |
| soil_low_c | -2.689085 | 9.291119 | -0.29 | 0.772 | -20.89934 | 15.52117 |
| labhc | -0.7380442 | 11.48615 | -0.06 | 0.949 | -23.25049 | 21.7744 |
| lablc | -3.150765 | 9.986153 | -0.32 | 0.752 | -22.72326 | 16.42174 |
| str_hc | -1.29142 | 6.696918 | -0.19 | 0.847 | -14.41714 | 11.8343 |
| str_lc | -9.031636 | 8.357229 | -1.08 | 0.28 | -25.4115 | 7.348232 |
| leg_hc | -35.57084 | 7.92673 | -4.49 | 0 | -51.10694 | -20.03473 |
| maize | -0.5611764 | 0.0893419 | -6.28 | 0 | -0.7362833 | -0.386069 |
I have three questions based on these results.
- Being that maize is the price variable, why is it reported in STATA from a mixlogitwtp command? Or rather, why aren’t the coefficient and standard error omitted?
- Should I modify my command?
- How do I interpret the results of the price variable (i.e., maize) in the following table?
Note-
The data includes participants' choices of one agricultural practice out of 2 alternatives or an opt-out option. Thus, participants decide between 3 choices for each hypothetical scenario. Each scenario entails an agricultural practice that includes 5 attributes with 3 levels (excluding the monetary attribute). The choice attributes you see in the table are in effects form and are defined as-
Attribute 1 - soil_high_c/soil_low_c indicate high or low soil fertility received from practice
Attribute 2 - labhc/lablc indicate high or low labor requirements demanded by practice
Attribute 3 - str_hc/str_lc indicate high or low Striga prevalence (a weed that parasitizes maize) received from practice
Attribute 4 - leg_hc/leg_lc indicate high or low legume yield received from practice
Attribute 5 - The monetary attribute is maize.
Status-quo is omitted from each attribute. So soil_med_c, labmc, str_mc and leg_mc are not foud in the mixlogitwtp command.
