Basically, this book is the result of my curiosity. Let me try to explain this.

Equipped with a mathematics degree and having completed my military service, I found myself, more or less accidentally, employed at the Netherlands’ Central Bureau of Statistics (now called Statistics Netherlands). Though not very explicitly formulated, the aim was that I should set up research in price statistics, because this was somehow found to be necessary – inflation was high in those years. After a while I had, I think, a fair idea of what all those price statisticians were doing, individually and collectively. But, though Mudgett's 1951 book, Index Numbers, was given to me as a sort of welcome present (in 1973), there was no research tradition at the office to continue. So I started looking at the then-current literature for clues – there was no Internet in those days, but, fortunately, the office had an excellent library – and, driven by internally and externally motivated research questions, gradually the field of theory opened up for me.

I learned that there were several approaches, going by names such as the “test approach,” “economic approach,” and “stochastic approach.” There was the rather arcane “Divisia approach,” and the even more obscure “factorial approach.” I traced back the history of ideas by looking at source materials. Meanwhile, a number of concrete problems came along for which practical solutions had to be found, such as the treatment of seasonal commodities, the choice between direct or chained indices, and the best way of making international price and volume comparisons.

The central questions that, in the background, kept me occupied through all those years are questions such as: What, exactly, is a price or quantity index?