What is spurious variable?

No. A discrete variable is one that takes discrete numerical values. But a discrete variable can be ordered while a nominal one cannot.Age, in years, is a discrete variable, and you can say that a...

Not always. It could be a constant. For example x is one variable, and y = x-2 is another variable. Then x - y = x - (x-2) = 2.

A manipulated variable the factor or quantity the investigator changes intentionally. This is established before doing the test. A controlled variable is a factor that may alter or affect the...

The independent variable.

dependent variable is the thing you measure in an experiment and a independent is the one you change.