Values for FVC and FEV1 that are over 80% of predicted are defined as within the normal range. The FEV1/FVC ratio is expressed as a percentage, and a normal young individual is able to forcibly expire at least 80% of his or her vital capacity in one second. A ratio under 70% suggests underlying obstructive physiology. However, the FEV1/FVC ratio declines as a normal sequelae of aging. Thus, at advanced ages, pathologic airways obstruction is diagnosed based upon deviation from predicted FEV1/FVC values, with values below the 5th percentile best selecting patients with obstructive defects.