​Hello and thank you for the inquiry. The Initial Patient Population, or IPP, is the population of patients from which the eCQM is calculated. For example, CMS108v10 Venous Thromboembolism Prophylaxis assesses the number of patients who received VTE prophylaxis or have documentation why no VTE prophylaxis was given between the day of arrival to the day after hospital admission or surgery end date for surgeries that start the day of or the day after hospital admission. In order to calculate the measure, VTE-1 establishes an initial population of inpatient hospitalizations for patients age 18 and older, discharged from hospital inpatient acute care without a diagnosis of venous thromboembolism (VTE) or obstetrics with a length of stay less than or equal to 120 days that ends during the measurement period. From this, the denominator of the measure is set to equal this initial population, while the numerator is set to include patients who met the requirement of having received VTE prophylaxis or who had a reason established why no VTE prophylaxis was given. For more information about eCQMs, please visit the Get Started with eCQMs page on the eCQI Resource Center at https://ecqi.healthit.gov/ecqms .