# Overview

Calculated fields exist in the Solution for which the denominator of the patient population is sometimes known, and sometimes unknown. Per CMS rules, no field can be displayed if the cell value is 10 or less. (See Data and Metrics - <11, ins, and hyphen "-"). However, when calculating certain measures, Trella Health increases the limits on the patient denominator to ensure statistical significance. If the statistical significance threshold is not met, a value of “ins” is displayed to denote “insignificant” patient population.

## Examples:

**Average Length of Stay (ALOS)**

Since ALOS is a metric calculated for a patient population that is solely within the confines of the agency to control, Trella Health displays this measure when the population of patients is >10 patients. Thus, if the number of patients is not <11, the ALOS will be displayed. Otherwise, “ins” is displayed.

**Performance Metrics**

Performance metrics are measures that typically involved another provider (e.g., hospitalizations and readmit rates). To ensure anomalies in the data are smoothed and a significant patient population is available, Trella creates these measures using a two-year population of patients. In this case, the threshold is 30 patients, otherwise “Ins” is displayed. This enables 30 patients for a denominator when creating two-year rates, and for one-year (rare) the threshold would be 15 patients. By calculating these rates in this way, we can display low rates by mandating a large denominator for the patient population, and calculating the measure over two years, ensuring the calculation cannot be applied to a patient count of one year.