fittedness

Fittedness is a general characteristic describing how well something is suited or adapted to a particular purpose, context, or dataset. The term is used across disciplines to denote the degree of compatibility between a model, function, or object and the conditions it is intended to operate within. In common usage, fittedness contrasts with misfit, where a thing is poorly matched to requirements.

In statistics and data analysis, fittedness refers to how closely a model's predictions align with observed data. Practitioners evaluate fittedness with residual analysis, goodness-of-fit measures such as R-squared, RMSE, AIC, cross-validation scores, and diagnostic plots. High fittedness implies accurate, generalizable predictions, but overfitting can produce misleadingly high fittedness on training data.

In natural and engineered systems, fittedness describes structural, functional, or behavioral compatibility with the environment. In biology, the term closest is fitness, referring to reproductive success; fittedness can describe the alignment of an organism's traits with ecological demands, or the degree to which a design matches operational requirements in engineering.

Measuring fittedness is context-specific and often involves comparing performance against a baseline, validating on independent data, or testing against predefined criteria. It is important to distinguish fittedness from raw accuracy, precision, or aesthetic appeal, as a high fit to one dataset can mask biases or limitations.

Related concepts include goodness of fit, model validation, calibration, and overfitting. The term is informal and its precise meaning should be defined within a given discipline.