# Metrics

- What is the StL Index?
- What is the difference between the Origin-Destination Traffic Index and the various Zone Traffic Index values?
- How do I interpret trips with the same origin and destination?
- Why are the number of trips normalized on an index?
- How does the StL Index differ from the sample trip count?
- How do you normalize GPS data?
- How do you normalize LBS data?
- Can I compare or combine Personal and Commercial Index Values?
- Can I compare Bicycle, Pedestrian, and Vehicular Metrics to each other?
- Where can I find the Project Sample Size?
- How do I determine whether my Project has a large enough sample size?
- How does Single Factor Calibration Work?
- Why might the sum of the O-D Indexes be less than the Zone Traffic Index value?
- Why might the sum of the O-D Indexes be larger than the Zone Traffic Index value?
- How are Average Trip Duration, Trip Length, Trip Speed, and Trip Circuity Calculated?
- What is Trip Circuity?
- How do you determine the home and work Locations for a device?
- How do you define Congestion? What is the difference between Congestion and Free Flow Factor?
- How do you derive trip purpose?
- Why are there values for invalid O-D pairs in my Metrics?