Checklist
Keep the ingredients of a ratio
The same ratio can hide two very different stories.
When it fits
- An experiment or dashboard reports only a composite rate, efficiency or cost-per-unit figure.
When to avoid it
- Additional data collection still needs a justified purpose and appropriate privacy controls.
Checklist
- The numerator and denominator are recorded with compatible scopes.
- Each component can be inspected over the relevant period or condition.
- The explanation identifies which component changed rather than celebrating the ratio alone.
Why it matters
Retain the component measurements as well as the final ratio. A change may come from its numerator, denominator or both. NIST's experimental-design guidance recommends preserving this information so later interpretation is not trapped inside a compressed number.
An example
Cost per resolved case can fall because costs fell or because many easy cases entered the denominator.
Check your result
You can reconstruct the ratio and explain the movement of its components.
Keep this limit in mind
- Additional data collection still needs a justified purpose and appropriate privacy controls.
Connected ideas
Useful withBuild an overall rate from totals
Evidence and sources
Supports
When an experimental response is a ratio, recording its component measurements preserves information that the ratio alone loses.
Collect only information justified by the question and relevant data-governance constraints.
Choosing Variables and Levels · Selecting responses and components