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Consumer Price Index
Bureau of Labor Statistics > Consumer Price Index > Methods > Quality Adjustment
Clothes dryers image

Quality Adjustment in the CPI: Clothes dryers

Item definition

The Entry Level Item (ELI) category of Washers and Dryers is part of the index for Major Appliances, and includes all full size and compact automatic clothes washers, clothes dryers, and washer/dryer combinations for use in the home. In this factsheet, we examine the regression model used in the quality adjustment of price data for clothes dryers.

CPI sample

The sample used for the new hedonic model included 160 observations. About 80 percent of observations were sourced from the web, while the remaining 20 percent were quotes from traditional, in-store collection. Most prices were from September 2020. There were 10 unique brands and 12 distinct outlets in the sample.    

Current Model

Table 1 presents the details of the current model used to quality adjust clothes dryers.

Table 1. Parameter estimates for the hedonic regression for clothes dryers
Variable Name DF Parameter Estimate Standard Error T Statistic Pr > |t| Tolerance Statistic

Intercept

 1 4.60152 0.13542 33.98 <.0001

Gas fuel source

 1 0.11235 0.01506 7.46 <.0001 0.95694

Capacity

 1 0.2371 0.01781 13.31 <.0001 0.71806

Number of temperature settings

 1 0.06847 0.01322 5.18 <.0001 0.65234

Steam cycle

 1 0.12649 0.02477 5.11 <.0001 0.34903

Wi-Fi connectivity

 1 0.05856 0.02324 2.52 0.0128 0.42933

Vent/clogged duct sensor

 1 0.05911 0.02233 2.65 0.009 0.53606

Combo unit (small & large drums)

 1 0.39312 0.03286 11.96 <.0001 0.69612

Non-white color

 1 0.09098 0.01951 4.66 <.0001 0.61949

Energy Star certification

 1 0.07493 0.02048 3.66 <.0001 0.51187

Note: This model contains a control variable for a specific outlet that is not used for quality adjustment.

Summary notes

  • Quality adjustments derived from hedonic regressions for clothes dryers were first incorporated into the CPI in October 2000. Since then, the model for dryers has been updated 4 times, including the update described here.

  • For clothes dryers, the characteristics that received the most focus during the model evaluation included capacity, number of cycles, and type of screen. A cross-tabulation of number of cycles and regular price indicate that average regular prices are little changed between 3 and 11 cycles but increase after 11 cycles. However, a dummy variable to indicate dryers with 11 or more cycles was insignificant when considering other price factors. Meanwhile, dummy variables for type of screen – no screen, numeric screen, and alpha-numeric screen – were significant in preliminary models but insignificant when other factors were added in subsequent models.

  • The new model retains 3 variables that were present in each model in 2000, 2005, and 2008: type (gas or electric), capacity, and number of temperature settings. The new model also retains the steam cycle variable that was introduced in the 2008 model. 

  • The new model does not include a parameter for electronic controls, a variable that was in each of the previous 3 models. This result was likely due to the increased presence of this feature, as more than 90 percent of observations in the sample of dryers used for modeling have electronic controls.

  • The new model adds 5 variables not in previous hedonic models, including Wi-Fi connectivity; Energy Star certification; Combo unit (2 dryer drums in 1 machine); non-white color, and vent / clogged duct sensor. 

  • In addition to electronic controls, characteristics that were included in modeling but determined to not be influential on price include interior drum light, see-through door, reversible door, stainless steel drum, and lint filter indicator. 

Data

Access data for major appliances in our online database.

Additional information

Additional information may be obtained from the Consumer Price Index Information Office by email or calling 202-691-7000. Information on the CPI's overall methodology can be found in the BLS Handbook of Methods.

Last Modified Date: April 5, 2024