I'm not very good at this. But I think we need to ask the question. Others could answer it better than me.
Scott Sumner tells me that Greece is considering issuing NGDP-linked bonds, where the amount the government pays to bondholders is proportional to Nominal Gross Domestic Product. Like Scott, I rather like the idea of NGDP-linked bonds. But they do have one potential downside compared to regular bonds, and we need to think about it.
If a government issues NGDP-linked bonds, it has an incentive to lie about NGDP statistics. It has an incentive to say that NGDP is lower than it really is, or really could be. Because the lower is NGDP, the less money the government has to pay to those who hold NGDP-linked bonds.
It's a bit like (though not exactly like) the incentive an individual has to lie about his income, and say that his income is lower than it really is, so he pays less income tax.
[Update: maybe "manipulate" is a better word than "lie".]