If a previously unpaid activity (donating blood) is paid then we often observe that this activity is reduced. In this paper, it is hypothesised that the price offered is taken as a proxy for the "market value" of the activity. Depending on how the actor valued the activity previously,...

In a two-stage oligopoly, with investment in the first stage and quantity or price competition in the second stage, there is a kind of Folk Theorem: We find (i) over-investment if the goods are substitutes and competition is in strategic substitutes, (ii) under-investment if we have either...