Quality Adjustment in the CPI: Girls’ Tops : 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: Girls’ Tops

Item definition

The Entry Level Item (ELI) category of Girls’ Tops is part of the index for Girls’ Apparel, and includes all types and styles of shirts, sweaters, cardigans, vests, activewear tops, and one-piece leotards and bodysuits in preschool and grade school girls' sizes. In this factsheet, we examine the regression model used in the quality adjustment of price data for girls’ tops.

CPI sample

The sample used for the new hedonic model included approximately 770 observations. The model was constructed using web-based information due to restrictions on data collection during the COVID-19 pandemic, unlike models from the past that had a mix of store and website data. There were more than 150 unique brands in the sample, and the top 10 brands accounted for 49 percent of observations. There were more than 50 distinct outlets in the sample, and the top five outlets accounted for 53 percent of observations.

Current Model

Table 1 presents the details of the estimation of the current model used to quality adjust girls’ tops.

Table 1. Parameter estimates for the hedonic regression for girls’ tops
Variable Name	DF	Parameter Estimate	Standard Error	t Value	Pr > \|t\|	Tolerance Statistic
Intercept	1	3.23801	0.0546	59.3	<.0001
Style: Partial Closure Pullover	1	0.1714	0.05313	3.23	0.0013	0.86813
Style: Cardigan	1	0.43989	0.06076	7.24	<.0001	0.75139
Style: Sweater	1	0.40204	0.06885	5.84	<.0001	0.76221
Style: Open Front Shirt	1	0.30707	0.06327	4.85	<.0001	0.85853
Style: Activewear Top	1	0.15675	0.05491	2.85	0.0044	0.85538
Style: Sweatshirt	1	0.37332	0.0515	7.25	<.0001	0.72616
Style: No Closure Pullover		Base
Type of Brand: Luxury	1	1.62855	0.22191	7.34	<.0001	0.86466
Type of Brand: National	1	0.25361	0.03381	7.5	<.0001	0.68902
Type of Brand: Private		Base
Sleeve Length: Long Sleeves	1	0.19434	0.03177	6.12	<.0001	0.65823
Sleeve Length: Short Sleeve & Sleeveless		Base
Features: Trim	1	0.11688	0.04034	2.9	0.0039	0.86943
Features: Screen Print	1	-0.10627	0.03071	-3.46	0.0006	0.73823
Features: No Features		Base
Fiber (continuous): Cotton	1	-0.00125	0.00042	-3.01	0.0027	0.77554
Fiber (continuous): Cashmere/Wool	1	0.01036	0.0035	2.96	0.0032	0.92586
Fiber (continuous): Polyester		Base
NOTE: This model contains control variables for type of business, type of store, and geographic region, but they are not used in adjustments.

Summary notes

Quality adjustments derived from hedonic regressions for girls’ tops were first incorporated into the CPI in December 1995. Since then, the model for girls’ tops has been updated six times.
Characteristics that received the most focus during the model evaluation include item style, type of brand, sleeve length, item features, and fiber content.
Two variables that surfaced as price differentiators were activewear tops and sweatshirts. No previous hedonic model for girls’ tops included an adjustment for these variables. In fact, all styles of tops but vests and bodysuits are accounted for in the model.
Fiber variables in the new model were not as significant as in previous models. For example, the last model iteration had three additional adjustments for synthetic fibers. This model found that only natural fibers were statistically significant.
Applique, embroidery, or applique-embroidery combination variables were included in many past models. In the new model, however, these feature characteristics were replaced by two others, trim and screen print, which were not as present in previous models but turned out to be significant in the new iteration.
Applique-embroidery and partial closure pullover were two prevalent interaction variables in previous models, but these only involved either style or feature characteristics. Until now, fiber content was not used in this way. The cashmere-wool interaction was calculated as a summation of fibers, and a parameter estimate was developed accordingly for use in adjusting both cashmere and wool fiber changes.

Data

Access data for Girls' 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: June 27, 2024