Quality Adjustment In The BLS Price Programs

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Quality Adjustmentin the BLS Price ProgramsSteven Sawyer, Producer Price ProgramAric Schneider, International Price ProgramRyann Watkins, Consumer Price ProgramData Users’ ConferenceApril 21, 20211— U.S. BUREAUOF LABORSTATI STI CS b l s. g ov

Quality AdjustmentOverviewAric SchneiderInternational Price Program2— U.S. BUREAUOF LABORSTATI STI CS b l s. g ov

IntroductionOverview – Why and What is Quality Adjustment2. When does BLS Quality adjust3. How we Adjust4. Questions1.3— U.S. BUREAUOF LABORSTATI STI CS b l s. g ov

Why and what is quality adjustment4— U.S. BUREAUOF LABORSTATI STI CS b l s. g ov

When to quality adjustOld and new products are comparable Explicit quality adjustment Cost-based Hedonic quality adjustmentChange in size/quantity Old and new products are not comparable New product previous price Price imputation5— U.S. BUREAUOF LABORSTATI STI CS b l s. g ov

When to quality adjust (cont.)6CPIPPIOld/new productscomparableDirect ComparisonDirect comparisonDirect ComparisonExplicit icsCost-BasedHedonics for computersChange size/quantityQuantity AdjustmentRatio methodLink AdjustmentNew productprevious price*new products previous pricenot usedOverlap methodDiscontinue and ReplacePrice imputationClass mean imputation andcell relative imputationLink to cell relativeDiscontinue and Replace— U.S. BUREAUOF LABORSTATI STI CS b l s. g ovMXPI

Quality Adjustmentfor Consumer PricesRyann WatkinsConsumer Price Program7— U.S. BUREAUOF LABORSTATI STI CS b l s. g ov

Consumer Price Index (CPI) quality adjustmentThe quality adjustment (QA) method is 1 of 3 methodsused when handling replacement items 3 methods used: Directly use price change Impute price change Adjust for quality changes– Occurs at the item level, not index level8— U.S. BUREAUOF LABORSTATI STI CS b l s. g ov

Consumer Price Index (CPI) quality adjustment: Why? Why do we use quality adjustments in the CPI? Items in the market basket sometime leave the marketplace andneed to be replaced Often, replacement items have quality differences and cannot becompared directly to the unavailable item This is where QAs come in!– QAs make it possible to compare different items across time periods9— U.S. BUREAUOF LABORSTATI STI CS b l s. g ov

Consumer Price Index (CPI) quality adjustment: When When do quality changes happen in the CPI? Quality changes in replacement items are most likely to occur during:Seasonal Changes(Mostly apparel items)Innovation andTechnological ChangesUpgrades to ExistingItems (model yearchanges for new vehicles)***Note: technological changes and upgrades are not mutually exclusive10— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

CPI quality adjustment: by the numbersNumber of CPI replacement items in 2020Item GroupTotalItemsItemswith LDTotalAverage11#%Replacement Replacement % Direct % Quality% NonItemsItemsComparison Adjusted comparable— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

CPI item checklists 12How do we know when the replacement item has a quality difference?“Item checklist”Each item has a checklist that capture all its important characteristicsData collectors use checklists to choose replacement itemsAnalysts review the characteristic changes to determine if there’s beenquality changes— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

CPI item checklist example: computersCategoryCharacteristic13— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

QA methods used in CPI Hedonic based QA method Uses statistical regression models to estimate the values of specificcharacteristics Data used to build models come from CPI sample or alternative datasources Examples: apparel items, televisions, cell phones Cost based QA method Exact monetary values are assigned to specific characteristics Values are obtained from manufacturers, alternative data sources,website information, etc. Example of items: new vehicles, computers14— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Hedonic based QAPurpose: Hedonic QAs remove the difference in quality between replacement items andunavailable items allowing us to show a better estimate of price changeData: Item’s CPI sample or alternative data sourceRequirements: Sample 100 observations and has sufficient variationRegression Equation (semi-log function):Log(Price) a β1x1 β2x2 . βnxn ɛ15— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Hedonic model example: women’s dressesVariableCategoryIndependentVariable (Xn)ParameterEstimate (βn)VariableCategoryIndependentVariable (Xn)ParameterEstimate (βn)FiberSpandex-0.00894SizeMisses, Petites, 0.00169No lining-0.10506Poly, Rayon, CottonbaseFull/partial liningbaseBridal1.23375Below knee0.05881Formal0.20270Knee and abovebaseCasualbaseLong sleeve0.12287Exclusive1.13463Short sleeve, sleevelessbaseBoutique0.89729ZipperbaseHigh end 508Special line private-0.15400Sequin, bead,rhinestone0.11495Private Brand Cat.16— U.S. BUREAUOF LABOR STATI STI CS b l s. g ovLiningLengthSleevelengthClosureFeatures

Hedonic based QA example: women’s dressesType of QualityChange17— U.S. BUREAUOld ItemReplacement ItemFiber100% Polyester60% Nylon 40%PolyesterType of DressCasual dressFormal dressLiningNo liningLiningClosureNo closureZipper closurePrice 125 250OF LABOR STATI STI CS b l s. g ov

Hedonic based QA example: calculation for women’s dresses1. Calculate the adjusted price of the old item, which will be usedto calculate the price change used in the indexPrice old item * 𝑒𝑒 (Σ ��𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 ��𝑒𝑒𝑒𝑒𝑒 Σ 𝑜𝑜𝑜𝑜𝑜𝑜 ��𝑒𝑒𝑒𝑒𝑒) Price adjusted old item 125 old item * 𝑒𝑒 ((0.101 0.203) ( 0.105 0.175)) 224.15adjusted old item18— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Hedonic based QA example: calculation for women’s dresses (cont.)2. Calculate the price change of the adjusted old price and thereplacement item’s price:[(Price replacement ̶ Price adjusted old item)/ Price adjusted old item] 100 Adjusted Price Change[( 250 ̶ 224.15)/ 224.15] 100 12% Adjusted price change used in indexNOTE: QA, in this case, is more accurate than directly comparing prices:[( 250 ̶ 125)/ 125] 100 100% Price change without QA (not used in index)19— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Cost based QAPurpose: Cost based adjustments also remove the difference in quality between replacement andunavailable itemsDifference from hedonic QA: Cost based adjustments use actual dollar values, not estimated dollarvalues from a regression modelData: Price & characteristic data provided by manufacturers, alternative data sources, and/or onlineinfoRequirements: Prices associated with specific characteristics are available20— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Cost based QA example: new vehiclesType of QualityChange21— U.S. BUREAU2020 Model(MSRP 33,550)2021 Model(MSRP 34,750)Reported ValueofCharacteristicInteriorNot standardSmartphoneintegration 50Transmission6 speedtransmission9 speedtransmission 399Remote/keyless entryNoYes (AutoStart/Stop) 459OF LABOR STATI STI CS b l s. g ov

Cost based QA example: calculation for new vehicles1.Calculate the adjusted price of the old item, which will be used to calculatethe price change used in the indexPrice old item New Characteristics– Old Characteristics Price adjusted old item 33,550 ( 50 399 459)– 0 34,458adjusted old item22— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Cost based QA example: calculation for new vehicles (cont.)2.Calculate the price change of the adjusted old price and the replacementitem’s price[(Price replacement ̶ Price adjusted old item)/ Price adjusted old item] 100 Adjusted Price Change[( 34,750- 34,458)/ 34,458] 100 0.85% Adjusted price change used in indexNOTE: QA, in this case, is more accurate than directly comparing prices:[( 34,750 ̶ 33550)/ 33550] 100 3.6% Price change without QA (not used in index)23— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Quality Adjustmentfor Producer PricesSteven SawyerProducer Price Program24— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Why the PPI quality adjustsContinual innovation and improvements across the U.S.economy means products change on a regular basis All of this change makes quality adjustment crucial to the PPI, amatched-model price index 25— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Common changes to goodsUpgraded parts Different materials Different physical properties Software 26— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Common changes to servicesTime Location Speed Activity Software 27— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Base prices and price relatives Price change is measured as the change in the ratio of the netprice (NP) to the base price (BP), known as the long-termrelative (LTR)ΔPrice 𝑁𝑁𝑁𝑁Δ𝐵𝐵𝐵𝐵 ΔLTRQuality adjustment involves changing the BP Product’s price can change because of a change in NP, BP orboth 28— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Explicit quality adjustmentUsed when a PPI Industry Analyst (IA) can obtain the change inproduction cost (typically from the respondent) associatedwith the change in the product Change in production cost also is called the value of qualityadjustment (VQA) 29— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Explicit quality adjustment formula 30𝐵𝐵𝐵𝐵𝑁𝑁𝑁𝑁𝑁𝑁 𝐵𝐵𝐵𝐵𝑂𝑂𝑂𝑂𝑂𝑂 ��𝑁𝑁𝑁𝑁𝑁𝑁𝑁 𝑉𝑉𝑉𝑉𝑉𝑉Denominator of the fraction, 𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁 𝑉𝑉𝑉𝑉𝑉𝑉, representsthe estimated net price of the old product in the month thesubstitution is made effective— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Explicit Quality Adjustment Example Price of a new model car is 14,000 and the price of theprevious year’s version is 13,500o 200 of that increase is due to the extra product cost andnormal margin associated with the addition of governmentmandated safety equipmento Pure price change is only 30031— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Explicit Quality Adjustment Example (cont.) Assume 𝐵𝐵𝐵𝐵𝑂𝑂𝑂𝑂𝑂𝑂 13,200𝐵𝐵𝐵𝐵𝑁𝑁𝑁𝑁𝑁𝑁 13,200 14,00014,000 200 13,391.3043Estimated price old model car in current period is 13,80013,500 𝐿𝐿𝐿𝐿𝐿𝐿𝑂𝑂𝑂𝑂𝑂𝑂 1.022713,20014,000 𝐿𝐿𝐿𝐿𝐿𝐿𝑁𝑁𝑁𝑁𝑁𝑁 1.045513,391.30431.0455 1.0227 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 0.02231.022732— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

PPI hedonic models Microprocessors Desktop Notebook Server Computers (jointly developed with IPP) Desktop Notebook Server 33Broadband high speed Internet service— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Computer hedonic QA �𝑪𝑪𝑪𝑪𝑪 𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑𝒑 𝒂𝒂 𝒃𝒃𝟏𝟏 𝑪𝑪𝑪𝑪𝑪𝑪 𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔𝒔 𝒃𝒃𝟐𝟐 𝑪𝑪𝑪𝑪𝑪𝑪 𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄𝒄 𝒃𝒃𝟑𝟑 𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴𝑴 𝒃𝒃𝟒𝟒 ��𝑺 𝒃𝒃𝟓𝟓 𝑶𝑶/𝑺𝑺34VariableQuantityCoefficient (a or b )Marked up costIntercept-100100CPU speed3.250160CPU cores42288Memory42080Storage7500.14105Operating system1100100Computer price--633— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Broadband hedonic QA examplelog(Broadband price) a 0.45log(Download speed) 0.61(Company A )OldNew4045Download 50speed75Price35— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov𝑉𝑉𝑉𝑉𝑉𝑉 𝑥𝑥1 𝑏𝑏1𝑦𝑦0 [(𝑥𝑥 )075 0.4540[(50) 8.00660.1(Business) 1]1]

Time dummy hedonic models𝒍𝒍𝒍𝒍𝒍𝒍 𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷𝑷 𝜶𝜶𝟎𝟎 𝑫𝑫𝒕𝒕 𝟏𝟏 ���𝟐) 𝜷𝜷𝒌𝒌 𝒍𝒍𝒍𝒍𝒍𝒍( 𝑿𝑿𝒌𝒌) 36Typically in log-log formSame form as hedonic quality adjustment model, but with a time dummy (𝐷𝐷(𝑡𝑡 1))Dataset is typically a two time period unbalanced panel (pooled cross-section)— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Time dummy hedonic models (cont.) Time dummy coefficient (Δ) gives an estimate of quality adjusted pricechange between time periods Price is directly adjusted Base price does not change 37Currently used in PPI Integrated microcircuits index— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Time dummy hedonic model examplelog(CPU price) a -0.02Dt 1 0.09log(CPU speed) 0.52log(CPU cores) 0.76log(Cache) 0.21log(Threads)Price change 𝑒𝑒 1 𝑒𝑒 0.02 1 -0.019838— U.S. BUREAU -1.98%OF LABOR STATI STI CS b l s. g ov

Microprocessors matched-model vs. timedummy hedonic indexOOfficial PPIIndexTime DummyHedonic Index39— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Ratio method Useful when the ratio of the old and new price are expected to be equalto the ratio of two values such as a quantity or size One associated with old product Another associated with new �𝐵𝑁𝑁𝑁𝑁𝑁𝑁 𝐵𝐵𝐵𝐵𝑂𝑂𝑂𝑂𝑂𝑂 ���𝑁𝑁𝑁𝑁 value corresponding to the new product𝑉𝑉𝑂𝑂𝑂𝑂𝑂𝑂 value corresponding to the old product40— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Ratio method example A ready-mix concrete company used to report prices by cubic yard andnow reports by truckload Mixer contains 8.5 cubic yards Price increased from 100/cubic yard to 850/truckloadIf the old base price is 95, then8.5𝐵𝐵𝐵𝐵𝑁𝑁𝑁𝑁𝑁𝑁 95 807.5000141— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Overlap method VQA not availableNet prices for both the old product and the new product are availablefor previous time periodRatio of the two net prices can be used to calculate a new base price:*in previous time period42— U.S. BUREAU𝐵𝐵𝐵𝐵𝑁𝑁𝑁𝑁𝑁𝑁 𝐵𝐵𝐵𝐵𝑂𝑂𝑂𝑂𝑂𝑂 OF LABOR STATI STI CS b l s. g ov𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁𝑁 ��𝑝 𝑁𝑁𝑁𝑁𝑂𝑂𝑂𝑂𝑂𝑂 ��𝑝

Overlap method (cont.) Method captures price changes between previous and currentperiod Input price changes Demand changes Other market changes43— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Overlap method example Tire company discontinues a passenger car tire No direct replacement available Respondent provides a tire from another product line that has been inproduction for a few months Previous month’s price for the old tire is 105 Previous month’s price for the new tire is 103 Current month’s price for new tire is 107 44If the old base price is 101, then— U.S. BUREAU𝐵𝐵𝐵𝐵𝑁𝑁𝑁𝑁𝑁𝑁OF LABOR STATI STI CS b l s. g ov 103 101 99.0762 105

Overlap example price change105 𝐿𝐿𝐿𝐿𝐿𝐿𝑂𝑂𝑂𝑂𝑂𝑂 1.0396101107 𝐿𝐿𝐿𝐿𝐿𝐿𝑁𝑁𝑁𝑁𝑁𝑁 1.080099.07621.0800 1.0396 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 0.03891.039645— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Link to cell relative Used with a non-comparable substitute No VQA available No overlap price available 46Method imputes a price change for the product Price change (the “cell relative”) equals the average price change forall products in the product’s lowest level index (“cell”) which actuallyhave good (non-imputed) prices— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Link to cell relative formula𝐵𝐵𝐵𝐵𝑁𝑁𝑁𝑁𝑁𝑁 ��𝑁𝑁𝑁𝑁𝑁𝑁𝑁 𝑒𝑒𝑒𝑒𝑒𝑒 𝑁𝑁𝑁𝑁where est NP represents the estimated net price (aka, cell relative) for the old product in the month thatthe substitution is made effective47— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Link to cell relative exampleSteel foundry provides a substitute casting Respondent cannot provide a VQA for the new casting andthere is no overlap pricing New casting price is 29.30, old casting price is 28.90, oldbase price is 26.70 and cell relative price is 33.50 29.30𝐵𝐵𝐵𝐵𝑁𝑁𝑁𝑁𝑁𝑁 26.70 23.5636 33.50 48— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Link to cell relative example price change28.9 𝐿𝐿𝐿𝐿𝐿𝐿𝑂𝑂𝑂𝑂𝑂𝑂 1.082426.729.3 𝐿𝐿𝐿𝐿𝐿𝐿𝑁𝑁𝑁𝑁𝑁𝑁 1.243423.56361.2434 1.0824 𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃𝑃 0.14871.082449— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Quality Adjustmentfor Import and Export PricesAric SchneiderInternational Price Program50— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Import and Export Price Index (MXPI) qualityadjustmentMXPI – Primarily explicit cost-based QA, quantity/sizeadjustments and new item replacements Hedonic modeling for computers and soon microprocessors MXPI uses a “link price” method to QA 51— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

How we capture this information52— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Quality adjustment - MXPI53— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

How we capture this information: cost associated with change54— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

How we capture this information: incomplete items55— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

How we capture this information: replace items56— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

MXPI explicit quality adjustmentPrice Ratio 𝐿𝐿𝑃𝑃𝑡𝑡 𝑃𝑃𝑡𝑡 1LPSTRLink Price (LP) used in place of New Price 𝑄𝑄𝑄𝑄 𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼𝐼 𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉𝑉 𝑡𝑡 𝐿𝐿𝐿𝐿𝐿𝐿𝑡𝑡 1 𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿𝐿 57— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Explicit cost-based quality adjustment MXPI Using the same scenario for an explicit QAthat Steve demonstrated:Pre-linkPricePercentChangeLink58— U.S. BUREAU202101202102202103 13,500.00 13,500.00 14,000.000.0%3.7%Price 13,800.00PercentChange2.22%OF LABOR STATI STI CS b l s. g ov

Quantity/size quality adjustment Again using the same example that Steve showed us using thePPI Ratio Method:Pre-linkPricePercentChangeLink59— U.S. BUREAU202101202102202103 100.00 100.00 850.000.0%0.0%Price 100.00PercentChange0.0%OF LABOR STATI STI CS b l s. g ov

New item replacement MXPINew Item Replacements are introduced as a New Series vs. acontinuation MXPI uses similar “link to cell relative” concept as the PPI MXPI again uses a similar “overlap” concept as PPI 60— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Contact informationSteve Sawyer, Senior EconomistProducer Price Programsawyer.steven@bls.govAric Schneider, Branch ChiefInternational Price Programschneider.aric@bls.govRyann Watkins, EconomistConsumer Price Programwatkins.ryann@bls.gov61— U.S. BUREAUOF LABOR STATI STI CS b l s. g ov

Hedonic based QA example: calculation for women's dresses (cont.) 2. Calculate the price change of the adjusted old price and the replacement item 's price: [(Price replacement ̶ Price adjusted od il tem)/ Price adjusted od il tem] 100 Adjusted Price Change [( 250 ̶ 224.15)/ 224.15] 100 12% Adjusted price change used in index

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