In other cases, we must rely on survey approaches to estimate WTP, usually through a variant of the contingent valuation approach, which generally involves directly questioning respondents for their WTP in hypothetical market situations.
( ( In ( other cases ) ) ( , ( we ( ( must ( ( rely ( on ( survey approaches ) ) ) ( to ( ( ( ( estimate WTP ) , ) usually ) ( through ( ( a variant ) ( of ( ( ( the ( contingent ( valuation approach ) ) ) , ) ( which ( generally ( involves ( directly ( ( questioning respondents ) ( for ( ( their WTP ) ( in ( hypothetical ( market situations ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (PP (IN In) (NP (JJ other) (NNS cases))) (, ,) (NP (PRP we)) (VP (MD must) (VP (VB rely) (PP (IN on) (NP (NN survey) (NNS approaches))) (S (VP (TO to) (VP (VB estimate) (NP (NNP WTP)) (, ,) (ADVP (RB usually)) (PP (IN through) (NP (NP (DT a) (NN variant)) (PP (IN of) (NP (NP (DT the) (JJ contingent) (NN valuation) (NN approach)) (, ,) (SBAR (WHNP (WDT which)) (S (ADVP (RB generally)) (VP (VBZ involves) (S (ADVP (RB directly)) (VP (VBG questioning) (NP (NNS respondents)) (PP (IN for) (NP (NP (PRP$ their) (NN WTP)) (PP (IN in) (NP (JJ hypothetical) (NN market) (NNS situations))))))))))))))))))) (. .)))
Hypothetical market situations are uniform across all respondents.
( ( Hypothetical ( market situations ) ) ( ( are ( uniform ( across ( all respondents ) ) ) ) . ) )
(ROOT (S (NP (JJ Hypothetical) (NN market) (NNS situations)) (VP (VBP are) (ADJP (JJ uniform) (PP (IN across) (NP (DT all) (NNS respondents))))) (. .)))