Automated methods provide hypopnea detection for determining a hypopnea event and/or a severity of a hypopnea event. In some embodiments, a calculated short-term variance of a measured respiratory flow signal are compared to first and second proportions of a calculated long-term variance of the measured flow signal. A detection of the hypopnea may be indicated if the first measure falls below and does not exceed a range of the first and second proportions during a first time period. In some embodiments, a hypopnea severity measure is determined by automated measuring of an area bounded by first and second crossings of a short-term measure of ventilation and a proportion of a long-term measure. The detection methodologies may be implemented for data analysis by a specific purpose computer, a detection device that measures a respiratory airflow or a respiratory treatment apparatus that provides a respiratory treatment regime based on the detected hypopneas.