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))))))))))))))))))) (. .)))
Surveys can estimate WTP by questioning respondents.
( Surveys ( ( can ( ( estimate WTP ) ( by ( questioning respondents ) ) ) ) . ) )
(ROOT (S (NP (NNS Surveys)) (VP (MD can) (VP (VB estimate) (NP (NNP WTP)) (PP (IN by) (NP (VBG questioning) (NNS respondents))))) (. .)))