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Substitution Errors

One character is replaced with a different character.

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One character is replaced with a different character.

Substitution errors occur when one character is incorrectly replaced with another. This often happens with visually similar characters (0 vs O, 1 vs l, 5 vs S) or adjacent keyboard keys. The string length stays the same, but one character is wrong. These errors are common in manual data entry.

Original: ABCD → Error: ABXD (C replaced with X)

  • 12345 → 12845 (3 replaced with 8)
  • JOHNSON → JOHNS0N (O replaced with zero)
  • AB-1234 → AB-1284 (3 replaced with 8)

How to recognize it

  • One character is different, all others match
  • Length remains the same
  • Often involves similar-looking characters

Common mistakes

  • Confusing substitution with transposition
  • Missing errors with visually similar characters (0/O, 1/l/I)
  • Not comparing character by character

Step-by-step walkthrough

Find the error: Original 'JOHNSON' vs Given 'JOHNS0N'

  1. Compare position 1: 'J' = 'J'
  2. Compare position 2: 'O' = 'O'
  3. Compare position 3: 'H' = 'H'
  4. Compare position 4: 'N' = 'N'
  5. Compare position 5: 'S' = 'S'
  6. Compare position 6: 'O' vs '0' - mismatch found
  7. Compare position 7: 'N' = 'N'
  8. The letter 'O' was replaced with the digit '0' (zero)

Answer: Substitution error: letter 'O' replaced with digit '0' at position 6

Practice guidance

Error Checking

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