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Score forecast accuracy with MAPE and bias, using restated actuals

  • For FP&A and financial analysts
  • You practice Catching mistakes and made-up facts
  • Time about 5 minutes
  • Level Intermediate

About this exercise

You're reviewing how well the revenue forecast has done. Write a prompt for plain text with lines starting "Jan:", "Feb:", "Mar:", "Apr:", "MAPE:" and "Bias:". Month lines show |forecast - actual| / actual as a percent to one decimal, with the numbers. MAPE is the average of the four, and Bias is total forecast minus total actual with its percent of actual. Use restated actuals. Under 80 words.

Common mistakes when you ask AI for this

  • Using the first reported April. The AI uses 112 and gets a 25.0% error. Try: Say: "Use the restated April actual of 100."
  • Dividing by forecast. The AI divides the error by the forecast instead of actual. Try: Add: "Percent error = |forecast - actual| / actual."
  • Missing bias math. The AI says 'over-forecast' without totals. Try: Say: "Bias = total forecast minus total actual, with percent of actual."
  • Wrong MAPE. The AI averages the dollar errors or skips the addition. Try: Add: "MAPE: average of the four percentages, with the addition."
  • Trusting the AI to count words. AI is bad at counting and runs past word limits. Try: Ask for fewer words than the real cap and keep each line short.

What a strong prompt includes

  • Names the six lines
  • Uses the restated figure
  • Gives the formula
  • Defines MAPE and bias
  • Caps length

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