travel behavior Air passenger duty 1 Contingent valuation method 1 Elasticity 1 Hierarchical linear modelling 1 United Kingdom 1 Willingness to pay 1 air transportation 1 close relationships 1 comparative study 1 connectivity 1 contingent valuation 1 demand elasticity 1 identities 1 mobility 1 pollution tax 1 psychology 1 questionnaire survey 1 social network 1 social networks 1 social status 1 tourism 1 transport psychology 1 travel demand 1 travel motivation 1 willingness to pay 1