Which of the following software metrics is based on a nominal scale-1

Nominal scales are used in measurement to categorize data without any order or priority.  They are the simplest form of measurement scale and are used to group items into distinct categories based on names or labels 1 2 3 .

Root cause of defect (Option A): This fits the nominal scale as it involves categorizing defects based on their root causes, such as logic errors or data definitions.  These categories are mutually exclusive and do not have a natural order 1 .

Severity of a defect (Option B): This is an example of an ordinal scale, not a nominal scale.  The severity levels (critical, major, minor) imply a ranking or order of importance or impact 2 .

Defect density (Option C) : This metric uses a ratio scale as it involves a quantitative measure (number of defects) relative to the size of the software (function points), which has a true zero point and allows for meaningful comparisons between measurements 2 .

Defect discovery rate (Option D) : This is also a ratio scale because it measures the rate of defect detection over time (number detected per day), which is a quantitative assessment that allows for arithmetic operations