"The Heaviness of Smoking Index (HSI) was developed as a test to measure nicotine dependence by using two questions from the Fagerstrom Tolerance Questionnaire and the Fagerstrom Test for Nicotine Dependence: time to first smoking in the morning and number of cigarettes per day. It uses a six-point scale calculated from the number of cigarettes smoked per day (1-10, 11-20, 21-30, 31+) and the time to first cigarette after waking (less than/equal to 5, 6-30, 31-60, and 61+ minutes). Nicotine dependence is then categorized into a three-category variable: low (0-1), medium (2-4), and high (5-6). HSI as a measure for assessing nicotine dependence may have significant floor effects among lighter smokers seen in non-clinical populations and the validity of the measure for assessing dependence in a general population may be questioned. Nevertheless, HSI is commonly used in both clinical and population surveys to assess dependence, and may provide a simple way for clinicians prescribing dependency-based treatments to classify their patients."