Size Groupings |
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Size Groupings |
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The process of creating the size groupings begins with ranking the securities of the New York Stock Exchange by market capitalization, then dividing them into ten portfolios of descending size (the first portfolio contains the largest companies and the tenth contains the smallest). Similarly sized AMEX and NASDAQ securities are then added to the ten portfolios. Most of the size groupings in the SBBI® database are drawn from the tenth portfolio, the one containing the smallest companies.
The 10a and 10b groupings split the tenth portfolio into two parts, also ranked by market capitalization, with 10b containing the smaller companies. This is equivalent to dividing the stocks into twenty portfolios, with portfolios 19 and 20 being the same as 10a and 10b. Ibbotson first published the 10a and 10b breakdown in 2001 (see Data by Year).
The 10w, 10x, 10y, and 10z groupings split the tenth portfolio into four parts, also ranked by market capitalization, with 10w containing the largest companies and 10z the smallest. This is equivalent to dividing the stocks into forty portfolios, with portfolios 37, 38, 39, and 40 being the same as 10w, 10x, 10y, and 10z, respectively. Ibbotson first published this breakdown in 2010 (see Data by Year).