Method for identifying one or more amino acid residues for substitution at a particular position in an immunological binding agent, the method comprising: a) providing a first database of VH and / or VL amino acid sequences grouped according to the subtype； b) provide a second database of VH and / or VL amino acid sequences grouped according to the subtype and selected for having at least one desirable functional property, in which the desirable functional property is improved stability, improved solubility, not aggregation, an improvement in expression and / or an improvement in refolding performance； c) determining the amino acid frequency for an amino acid residue at a frame region position of the first database and at a corresponding frame region position of the second database； d) determine the enrichment factor (RF2: RF1) of the amino acid by establishing the ratio between the relative frequency of a residue within the second database (RF2) and the relative frequency of a residue within the first database (RF1) ) e) identify amino acid residue (i) as a preferred amino acid residue for substitution at the corresponding amino acid position of the immunological binding agent when the amino acid has an enrichment factor of more than 1, or (ii) as a residue of amino acid to be excluded at the corresponding amino acid position of the immunological binding agent when the amino acid residue has an enrichment factor of less than 1.Método para identificar uno o más residuos de aminoácido para sustitución en una posición particular en un agente de unión inmunológica, comprendiendo el método: a) proporcionar una primera base de datos de secuencias de aminoácidos de VH y/o VL agrupadas según el subtipo； b) proporcionar una segunda base de datos de secuencias de aminoácidos de VH y/o VL agrupadas según el subtipo y seleccionadas por tener al menos una propiedad funcional deseable, en el que la propiedad funcional deseable es estabilidad mejorada, solubilidad mejorada, no ag
