住房价格仍在下降，但住房成本却使一项重要的通货膨胀指数没有降下来。

　　美国劳工统计局（Bureau of Labor Statistics）周五将公布4月份的消费者价格指数（CPI）。经济学家们的平均预期值是，CPI指数在3月份小幅下挫后4月份将维持前月的水平。他们还普遍认为，4月份不包括食品和能源价格的核心CPI有可能上升0.1%.

　　迄今为止，在核心CPI中占据最大权重的是所谓“自有房屋市场租赁价格”（OER）。这一指标试图衡量房主自住房屋的市场租赁价格。这一指标在CPI中的权重占24%，在核心CPI中的权重占31%.

　　今年3月，美国的OER较上年同期上涨了2.1%，超过了核心CPI 1.8%的增速。但OER的增速却低于房屋租赁成本的增速，后者在CPI中的占比要小得多，该指标3月份较上年同期上涨了3.2%.

　　为什么房屋租金涨幅和自有房屋的市场租赁价格涨幅会有不同？原因之一是美国劳工统计局在统计OER时会将公用事业成本从租金成本中减去，这是因为房客通常并不需要支付取暖费和水费等公用事业费用，而房主却要支付这笔费用。有时这一差别会导致OER涨幅和房屋租金涨幅出现不一致，特别是当能源成本像去年那样居高不下时。

　　但长期而言，OER却会受到房屋租金上涨的推动。与一些人认为的不同，OER并不是反映拥有一套住宅所需花费成本的指标。在泡沫经济时代，美国许多地区的住宅拥有成本比住房租金要高得多，这导致OER反映的住房成本可能存在低估。

　　既然现在许多人正在失去住房，被迫租房居住，因此美国一些地区的房屋租金涨幅要高于住宅拥有成本涨幅。由于OER指标是与房屋租金挂钩的，因此它反映的住房成本现在可能开始出现高估，从而对CPI起了推升作用。

　　美国劳工统计局表示，从2010年起，OER在CPI中的权重可能会下降，以反映消费者偏好从拥有住房向租赁住房的转变。

　　美国联邦储备委员会（Federal Reserve）喜欢用美国商务部统计的个人消费支出价格指数（PCE）来衡量消费价格变动情况。房屋租赁成本在这一指数中的权重已经大幅降低，房租和OER两项合计只在PCE指数中占据18%的权重。

　　但市场却更看重CPI指数，而由于OER指标的影响，CPI指数反映的通货膨胀状况可能不久就将出现高估。

　　Housing prices are still falling， but housing costs are propping up a key inflation index.

　　The Bureau of Labor Statistics releases its April consumer-price index on Friday. Economists， on average， think CPI was unchanged after shrinking a bit in March. The so-called core CPI， which strips out food and energy， likely rose 0.1%， says the consensus.

　　The biggest component， by far， of core CPI is a mythical beast called 'owners' equivalent rent.' OER tries to gauge the market rent price of an owner-occupied residence. It makes up 24% of the CPI and 31% of core CPI.

　　In March， OER was up 2.1% from a year ago， outpacing the 1.8% growth in core CPI. But it was lower than rental costs —— a much smaller part of CPI —— which were up a whopping 3.2% year over year.

　　Why the difference between rent and OER？ One reason is that the Bureau of Labor Statistics builds OER by subtracting utility costs from rental costs， because tenants often don't have to pay for utilities such as heat and water， but homeowners， quite painfully， do. This can sometimes cause a gap between OER and rent， particularly when energy costs are high， as they were last year.

　　But OER in the long term is driven by rent. It is not， as some might think， a measure of the cost of owning a home. During the bubble， homeownership costs got much higher than rents in many areas， causing OER to potentially understate housing costs.

　　Now that people are losing their homes and being forced into the rental markets， rents are rising in some areas faster than homeownership costs. Because OER is tied to rent， it might start to overstate homeownership costs， keeping CPI higher.

　　Starting in 2010， the BLS notes， OER might get a smaller CPI weighting， to mark the shift in consumer preferences from owning to renting.

　　The Federal Reserve's preferred measure of consumer inflation， the Commerce Department's personal consumption expenditure price index， already assigns much lower weighting to rents —— rent and OER combined make up 18% of core PCE.

　　But the market focuses more on CPI， which thanks to OER might soon be overstating inflation a bit.