Interval level of measurement is the third level of measurement, which builds upon the nominal and ordinal levels. Variables at the interval level possess all the characteristics of ordinal variables but also have equal intervals between the categories. However, the interval level does not have a true zero point, meaning that the value of zero does not represent the absence of the variable being measured. In interval measurement, the differences between values are meaningful and can be quantified, but ratios or proportions between values are not meaningful.
Key characteristics of interval variables are:
1. Distinct Categories: Like nominal and ordinal variables, interval variables have distinct categories or groups.
2. Order or Ranking: Interval variables have an inherent order or ranking among the categories, similar to ordinal variables.
3. Equal Intervals: Interval variables have equal intervals or differences between adjacent categories. The intervals are consistent and measurable.
4. No True Zero: The interval level does not have a true zero point, where zero represents the complete absence of the variable being measured.
Examples of interval variables include:
• Temperature: Temperature measured on the Celsius or Fahrenheit scales. The intervals between degrees are equal, but zero does not represent the complete absence of temperature.
• Dates: Calendar dates, where the differences between dates are meaningful, but there is no true zero point.
• IQ Scores: Intelligence quotient (IQ) scores, where the differences between scores are meaningful, but zero does not represent the absence of intelligence.
In statistical analysis, interval variables can be summarized using measures of central tendency (mean, median) and measures of dispersion (standard deviation). Additionally, parametric statistical tests, such as t-tests or analysis of variance (ANOVA), are commonly used for analyzing interval data. However, it is important to note that ratios or proportions between interval variables are not meaningful due to the lack of a true zero point.
