When it comes to evaluating a tail, which matters more: its length or its shape? The answer, of course, is largely a matter of personal taste. But Douglas Galbi argues, compellingly, that we have been so focused on long tails and short tails that we have forgotten that tails of all lengths can come in an infinite variety of shapes. And those shapes – the slopes the tails form – are not fixed. They can change, and change dramatically, over time – even if (and this is important) the number of items in the tail remains the same. Here’s Galbi:
For a concrete example, consider the popularity of the ten-most-popular given names. The set of possible given names (given names on offer) is huge, and probably hasn’t changed much in the past two-hundred years. However, the popularity of the ten-most-popular given names for males in England has fallen from about 85% in 1800 to about 28% in 1994. If you want to understand changes in the popularity of the most popular items in a collection of symbols instantiated and used in a similar way, try to understand this change.
The shape of demand in a market, in other words, depends on many factors beyond just the number of items on offer, and it can vary independently of that number. Galbi believes “that size, which tail authorities have categorized as long or short, matters less than shape.” So could it be that, when it comes to the pattern of demand in a market, even a market or purely informational goods, the effect of the Internet may be considerably less important than we currently assume?
UPDATE: On a related note, Chris Edwards takes a close look at Jakob Nielsen’s drooping tail. Plotting a demand curve on a linear scale, it appears, may mask important variations in tail shape that become clear when the curve is plotted on a logarithmic scale. Edwards and Nielsen come to different conclusions about what one particular (and probably common) tail shape may mean.
UPDATE 2: Chief Long Tailer Chris Anderson has also been thinking about tail shape and in particular the differences between the classic long tail (powerlaw) and the drooping tail (lognormal). (Anderson has also posted a presentation on the subject that he gave at Google last weekend.) “The difference between those two curves,” he writes, “is the subject of a lot of research at the cutting edge of complexity theory, and the simple answer seems to be that it comes down to the nature of the network effects that create unequal (‘rich get richer’) distributions such as the powerlaw and lognormal in the first place.” Anderson’s focus on network effects as the ultimate determinant of demand patterns seems in line with Edwards’s focus on the nature and dynamics of linking in a market. Galbi’s view seems very different; he seems to be warning against trying to explain a market’s demand pattern solely in terms of network effects or any other universal “laws.” Markets are messier than that, is what (I think) he’s implying. My own sense – and I speak here as an ignorant bystander – is that the long tail and the drooping tail are overarching themes that provide a great deal of insight into the workings of markets in general but that don’t necessarily provide all that much help in understanding variations on those themes – and all real markets will, to one extent or another, be variations on the themes.