Quality Adjustment in the CPI: Women’s Bras : U.S. Bureau of Labor Statistics

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Bureau of Labor Statistics > Consumer Price Index > Methods > Quality Adjustment

Quality Adjustment in the CPI: Women’s Bras

Item definition

The item Women’s Bras is part of the index for Women’s Apparel. It is nested inside the Entry Level Item (ELI) and Item Stratum for Women’s Undergarments, Nightwear, Shapewear, and Swimwear. Here, we examine the hedonic regression model used in the quality adjustment of price data for women’s bras.

CPI sample

The sample used for this hedonic model included 943 observations from an extract of CPI data from August and September 2023 as well as webscraped data from a large national retailer. The CPI data was collected using a larger than usual amount of web-based information due to restrictions on data collection during the COVID-19 pandemic. Basic bras make up about 77 percent of the sample, and national brands comprise 63 percent.

Current Model

Table 1 presents the details of the estimation of the current model used to quality adjust women’s bras.

Table 1. Parameter estimates for the hedonic regression for women’s bras
Variable Name	DF	Parameter Estimate	Standard Error	T Statistic	Pr > \|t\|	Tolerance Statistic
Intercept	1	3.91796	0.01993	196.59	<.0001
Type: Basic, longline, sports bras		Base
Type: Nursing bras	1	-0.15164	0.07489	-2.02	0.0432	0.92759
Brand: Boutique	1	0.57323	0.04309	13.3	<.0001	0.68912
Brand: High/premium national	1	0.29465	0.02554	11.54	<.0001	0.85792
Brand: National		Base
Brand: Private	1	-0.09167	0.03656	-2.51	0.0123	0.73734
Brand: Miscellaneous	1	-0.53681	0.16823	-3.19	0.0015	0.96682
Closure: Opens partly or completely with front or back fastener		Base
Closure: Pullover with no fastener	1	-0.13874	0.02258	-6.15	<.0001	0.9705
Fiber: Spandex	1	0.00363	0.000963	3.76	0.0002	0.89707
Fiber: Nylon, polyester, rayon		Base
Fiber: Cotton	1	-0.00228	0.00044	-5.2	<.0001	0.93626
Note: This model contains control variables for type of business and country of origin, but they are not used in adjustments.

Summary notes

This is the second-ever CPI quality adjustment model for women’s bras, but the first to be used in practice. It was made possible by the use of webscraped data to supplement the CPI sample. This means that fewer women’s bras substitutions will be deemed non-comparable and imputed so long as a model is in use.
- This is the second hedonic model created for CPI-Apparel that utilizes alternative data.
The most important specifications in evaluating substitutions for women’s bras are type, brand type, and fiber content. All of these were included in the model.
Multipacks are rare for women’s bras and were not included in the quality adjustment model.
Other characteristics like underwire and lining were found to not be statistically significant.

Data

Access data for Women's Apparel 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: February 23, 2024