"The CPI market basket is developed from detailed expenditure information provided by families and individuals on what they actually bought." https://www.bls.g

"The CPI market basket is developed from detailed expenditure information provided by families and individuals on what they actually bought." https://www.bls.gov/cpi/questions-and-answers.htm#Question_3 https://www.bls.gov/cpi/questions-and-answers.htm#Question_3 So if families are buying in lower quantities then yes it would be accounted for.