I have not read Piketty, but like many in my position I will not let that stop me talking about the debate of his book focusing on data interpretation.
After leaving university I worked for a number of oil industry related consultancies, the formative time being spent with a firm that made their money by providing expert witness testimony in legal disputes around the revenue split from oil fields that crossed legal, often and lucratively international, boundaries. The charismatic founder of the consultancy, a Napoleonic Inverness-ite, liked to tell the junior technical staff that lawyers started with a case and gathered the evidence, where as scientists gathered the evidence to build a case. Now that I am older I wonder if this was more nuanced than I imagined in my twenties: scientists will gather evidence in order to answer the question at hand, they do not, as Francis Bacon seems to suggest, just gather the data and watch the science precipitate out of it.
In the early '90s the firm realised that there was money to be made in 'data management': collating the information on an oil reservoir, cleaning it up and delivering it to oil companies for their technicians to interpret. The boss was happy to provide this service for paying customers, but for the consultancy work of his firm, the interpreters gathered and cleaned up the data. The reason for this is that in the process of collating the information the interpreter develops deep tacit knowledge of strengths and weaknesses in the data that goes on to inform the interpretation. Most data sets are incomplete, clearly contain errors and in the process the interpreter needs to make judgements about how the data is manipulated to make it coherent. Understanding this helps in the analysis.
The Financial Times has identified manipulations in Piketty's data set, and no doubt the journalists who did this felt they were on to a significant scoop relating to the intellectual phenomena of the year. I think this highlights the journalist's unfamiliarity with the scientific process rather than problems with Piketty's work. I am immediatley reminded of Pierce's pragmatic metaphor of science: it is a cable not a chain. What this means, is that a chain fails when a link breaks where as a cable can suffer the breakage of a number of strands before it fails. The evidence is the Forth Road suspension bridge that has microphones attached to its ageing cables counting the strands that have broken to inform on its integrity.
The FT journalists were able to identify the issues with the data because Piketty had made so much data available for review. It is difficult to criticise his science because of this basic fact. The FT has raised doubts about the data, and he has responded with a justification, the justification that as someone experienced with interpreting data, I would expect. Again his science is difficult to fault. If we are going to claim that because he had to clean up the raw data, his conclusions are unsound, we need to be prepared to write of the vast majority of science, ancient and modern. I would start with the discovery of the Higgs Boson, for example. I think the UK (and possibly US) are in the midst of a real crisis of science because of the obsession we have with "the data" at the expense of the process (see my previous post).
I have not read Piketty's book but I will, I will do so on the basis that I am dubious about his conclusions and I base this doubt on an intuition that he believes that capitalism inevitably leads to wealth inequality. I see this is a marxist (as distinct from Marxist) interpretation that rests on a sense of determinism. I believe that capitalism can take on many characters, just as eating is done differently in East Asian and West European cultures. In this respect we can construct a capitalism that does not lead to wealth inequality. (Of course, this may rest on how capitalism is defined, if it is defined on the basis of profit maximisation rather than market exchange, there is no hope for capitalism, in my opinion).