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What does the interval scale measure?

1. Qualitative differences only

2. Ordering without fixed distances

3. Equal intervals between values

4. A fixed starting point

The correct answer is: Equal intervals between values

The interval scale is designed to measure quantitative differences among data points, ensuring that there are equal intervals between values. This characteristic allows for meaningful comparisons of magnitude. For example, in temperature measurements in Celsius or Fahrenheit, a difference of 10 degrees reflects a consistent increase in temperature, just as a difference of 20 degrees does. This scale does not possess an absolute zero point, which means that while it shows relationships among values (like their order and the magnitude of differences), it does not accurately convey ratios of measures. Thus, when discussing concepts like temperature, you can say that 20 degrees Celsius is ten degrees warmer than 10 degrees, but you cannot say that 20 degrees Celsius is twice as hot as 10 degrees Celsius due to the lack of a true zero. The other options describe characteristics that do not align with the definition of the interval scale. Qualitative differences pertain more to nominal scales. The notion of ordering without fixed distances suggests a rank order scale, which lacks the uniformity of intervals. Lastly, a fixed starting point refers to ratio scales, which differ from interval scales in their treatment of zero as a definitive absence of the quantity being measured.