Which statement accurately describes an interval scale?

An interval scale is defined by its ability to allow for ranked observations while also ensuring that the differences between the values are meaningful and consistent. This means that on an interval scale, not only can the items be ordered or ranked, but the intervals between the ranks are equal and meaningful, which facilitates the comparison of the differences across the scale. For instance, if we consider temperature measured in degrees Celsius, the difference between 20 degrees and 30 degrees is the same as the difference between 30 degrees and 40 degrees; this consistency in difference is a hallmark of interval scales.

The other statements fail to accurately describe an interval scale. While one might categorize data (as in the first option), an interval scale is specifically about ranking and measuring differences. A true zero point is a characteristic of ratio scales, not interval scales, which is why the second option is incorrect. Finally, the fourth option mentions qualitative attributes, but interval scales are inherently quantitative, measuring numerical values rather than qualitative categories.