Dear Economist,

为什么我在繁华商业街上找一条合适的裤子就那么难呢？作为一个腰围33-34英寸、高5英尺11英寸的男性，我认为自己的体型算是中等。然而，合适的衣服似乎总是脱销。经济学理论能解释这一点吗？

Why is it so hard for me to find a properly fitting pair of trousers on the high street? As a 33-34in waisted, 5ft 11in male, I consider myself of average build. Yet appropriate attire¹ always seems to be out of stock. Can economic theory shed any light on this?

焦虑的买裤人

Concerned Trouser Consumer

亲爱的买裤人：

Dear Trouser Consumer,

这里显然可以运用的经济分析是，哈罗德o霍特林(Harold Hotelling)在1929年发表的关于产品差异化的著作。霍特林设想有两个冰淇淋小贩，他们试图确定摊位在海滩上的位置。

The obvious economic analysis here is Harold Hotelling's 1929 classic on product differentiation². Hotelling imagined two ice-cream stands trying to decide where to locate on a beach.

霍特林的结论是，他们的摊位最终将背靠背地设置在（海滩）中央，每个消费者都会去最近的摊位。类似，主要政治党派也倾向聚集在政治谱系的中央。

His conclusion was that they would end up side-by-side in the middle, with each customer going to the nearest stall. Similarly, major political parties tend to cluster in the centre of the political spectrum³.

我们不会看到有公司专门生产单一尺码的裤子；如果发生这种情况，你就会有大量适合自己的裤子。一个较好的解释是，公司进行着"战略性产品差异化"，以避免竞争。对于霍特林设想的冰淇淋小贩而言，这意味着将摊位设在海滩的两端。对于竞争的公交公司而言，这意味着一家公司在整点和半点发车，另一家在整点前后一刻钟发车。

We do not see companies specialising in a single size of trouser; if we did, you would be swamped with pairs that fitted you well. A better explanation may be that companies are engaging in "strategic product differentiation" to avoid competition. For Hotelling's ice-cream vendors⁴, that would mean locating at opposite ends of the beach. For rival bus companies it would mean one service departing on the hour and half hour, the other at quarter to and quarter past.

在每个案例中，目的都是赋予两家公司提价的能力，同时又不让它们失去太多的消费者。

In each case the aim is to give both companies the ability to raise prices without losing too many customers.

在你的案例中，战略性产品差异化意味着一家服装店卖腰围32英寸、36英寸和40英寸的裤子。另一家店卖腰围30英寸、34英寸和38英寸的裤子。

In your case, strategic product differentiation would mean that one clothes store offers trousers with a 32in, 36in and 40in waist. The other offers 30in, 34in and 38in.

如果你去了错误的店，你就永远不会得到满意的结果；正确的店会提供合适的服装，但由于缺乏竞争，价格会偏贵。我承认这是一种古怪的经济理论。

If you are shopping at the wrong store you will never be satisfied; the right store would supply clothes to fit, but prices would be higher for lack of competition. It is a bizarre economic theory, I agree.

但这能解释你经常受挫的原因。

But it would explain your commonplace frustration⁵.