Credit-assignment schemas are widely applied by providing fixed or flexible credit distribution formulas to evaluate the contributions of coauthors of a scientific publication. In this paper, we propose an approach named First and Others (F&O) counting. By introducing a tuning parameterαand a weightβ, two new properties are obtained: (1) flexible assignment of credits by modifying the formula (with the change ofα) and applying preference to the individual author by adjusting the weights (with the change ofβ), and (2) calculation of the credits by separating the formula for the first author from others. With formula sepa-ration, the credit of the second author shows an inflection point according to the change ofα. The developed theorems and proofs concing the modification ofαandβ reveal new properties and complement the base theory for informetrics. The F&O schema is also adapted when considering the policy of ’first-corresponding-author-emphasis’. Through a comparative analysis using a set of empirical data from the fields of chemistry, medicine, psychology, and the Harvard survey data, the performance of the F&O approach is compared with those of other methods to demonstrate its benefits by the criteria of lack of fit and coefficient of determination.