住房價格仍在下降，但住房成本卻使一項重要的通貨膨脹指數沒有降下來。

　　美國勞工統計局（Bureau of Labor Statistics）周五將公布4月份的消費者價格指數（CPI）。經濟學家們的平均預期值是，CPI指數在3月份小幅下挫后4月份將維持前月的水平。他們還普遍認為，4月份不包括食品和能源價格的核心CPI有可能上升0.1%.

　　迄今為止，在核心CPI中占據最大權重的是所謂“自有房屋市場租賃價格”（OER）。這一指標試圖衡量房主自住房屋的市場租賃價格。這一指標在CPI中的權重占24%，在核心CPI中的權重占31%.

　　今年3月，美國的OER較上年同期上漲了2.1%，超過了核心CPI 1.8%的增速。但OER的增速卻低于房屋租賃成本的增速，后者在CPI中的占比要小得多，該指標3月份較上年同期上漲了3.2%.

　　為什么房屋租金漲幅和自有房屋的市場租賃價格漲幅會有不同？原因之一是美國勞工統計局在統計OER時會將公用事業成本從租金成本中減去，這是因為房客通常并不需要支付取暖費和水費等公用事業費用，而房主卻要支付這筆費用。有時這一差別會導致OER漲幅和房屋租金漲幅出現不一致，特別是當能源成本像去年那樣居高不下時。

　　但長期而言，OER卻會受到房屋租金上漲的推動。與一些人認為的不同，OER并不是反映擁有一套住宅所需花費成本的指標。在泡沫經濟時代，美國許多地區的住宅擁有成本比住房租金要高得多，這導致OER反映的住房成本可能存在低估。

　　既然現在許多人正在失去住房，被迫租房居住，因此美國一些地區的房屋租金漲幅要高于住宅擁有成本漲幅。由于OER指標是與房屋租金掛鉤的，因此它反映的住房成本現在可能開始出現高估，從而對CPI起了推升作用。

　　美國勞工統計局表示，從2010年起，OER在CPI中的權重可能會下降，以反映消費者偏好從擁有住房向租賃住房的轉變。

　　美國聯邦儲備委員會（Federal Reserve）喜歡用美國商務部統計的個人消費支出價格指數（PCE）來衡量消費價格變動情況。房屋租賃成本在這一指數中的權重已經大幅降低，房租和OER兩項合計只在PCE指數中占據18%的權重。

　　但市場卻更看重CPI指數，而由于OER指標的影響，CPI指數反映的通貨膨脹狀況可能不久就將出現高估。

　　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.