Handout 5.2: The relationship between accuracy, informativeness and scale of measurement

Name       Real weight     Interval    Ordinal       Nominal      
           (Ratio)                                                
Esther     90              100         100  (1)      3            
Mary       100             110         110  (2)      1            
Susan      130             140         120  (3)      2            
Shari      180             190         130  (4)      5            
Jim        360             370         140  (5)      4            

With ratio data, we can accurately say that Jim weighs twice as much as Shari.

With interval data, our scale is off so that we don't have a perfect zero (we are weighing everything 10 pounds too heavy). The result is that we can't make ratio statements. Note that with our slightly inaccurate scale, Jim does not receive a weight that is twice as much as Shari's.

With ordinal data, we can say who is heavier than who, but we don't know how much heavier they really are. We could get ordinal data if we just ranked people in terms of their weights or if our scale was less accurate at higher weights.