Question 30
UnclassifiedMean Absolute Percentage Error (MAPE) is undefined when:
Correct answer: B
Explanation
MAPE is calculated by dividing the absolute error by the actual value, then averaging the percentages. When an actual value is zero, that division becomes impossible because it causes division by zero, so MAPE is undefined.
Why each option is right or wrong
A. Predictions are large
B. Actual values include zero, causing division by zero
MAPE is computed as \(\frac{1}{n}\sum \left|\frac{A_t-F_t}{A_t}\right|\times 100\), so the actual value \(A_t\) sits in the denominator of each term. If any actual observation is 0, the percentage error for that point requires division by zero, which is mathematically undefined and makes the overall MAPE unusable for that dataset.
C. Predictions are negative
D. Sample size is small