This model is based on least-squares estimation.
最小二乗法 is the full term for 'least-squares method'; 最小二乗 is the shorter attributive form used in compounds.
least-squares method
Standard kanji spelling for the mathematical term.
Variant using numeral ２; common in technical writing.
Compound of 最小 (minimum) and 二乗 (square), calque from English 'least squares'.