Simply put, quantitative measurements deal in quantities. They are numeric values such as the total number of members, revenue in dollars, web page views, number of Story Points completed, and so on.

Qualitative metrics relate to the qualities of something. They reflect the sentiments of a person expressed as feelings, opinions, views, or impressions. Examples of qualitative metrics include customer satisfaction and team member happiness.

Sometimes we'll combine both quantitative and qualitative measurements. For example, we judge ease of maintenance for software on:

1. Cyclomatic complexity: A quantitative measurement of the number of independent paths through our code; the more paths, the harder it is to maintain
2. Ease of last change: A qualitative metric based on the Development Team's viewpoint; the harder it feels to make the previous code change, the harder the codebase is to maintain

More often than not, we can translate qualitative measurements into numbers, for example, rating customer satisfaction with our product on a scale of 1 to 10, one being very unhappy, ten being very happy. However, if we don't also capture the individual's verbal response as to why they are feeling particularly happy or unhappy, then the metric over time may become meaningless. For example, we won't be able to address a downward trend in customer happiness unless we know why people are unhappy, and there is likely to be more than one reason.

Also, "value" means many things to an organization, so we have to measure each aspect of it, that is, direct revenue, reduced costs, return on investment, and so on. Sometimes value is easily quantifiable, for example when a User Story directly produces revenue. Other times it requires feedback from our customer, telling us whether what the team is building is meeting their needs.