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9618 · 6.2

Data Integrity — practice questions

Practice and worked examples for 9618 Data Integrity. Short previews only — attempt the full question in MarkScheme against the official scheme.

Worked example 1

An ordering system uses 6-digit product codes. The 7th digit is a check digit calculated using the modulus-11 method with weights 7, 6, 5, 4, 3, 2. Calculate the check digit for the product code 830154.

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  1. Multiply each digit by its corresponding weight: (8 × 7) + (3 × 6) + (0 × 5) + (1 × 4) + (5 × 3) + (4 × 2) = 56 + 18 + 0 + 4 + 15 + 8

  2. Sum the results: Sum = 101

  3. Find the remainder when the sum is divided by 11: 101 ÷ 11 = 9 remainder 2 Remainder = 2

  4. Subtract the remainder from 11: Check value = 11 - 2 = 9

  5. Determine the final check digit: If the result is 11, the check digit is 0. If the result is 10, the check digit is 'X'. Otherwise, the result is the check digit. Here, the result is 9.

    The check digit is 9. The full product code would be 8301549.

Worked example 2

A hospital clerk is entering a patient's National Health Service (NHS) number, 123 456 7890, from a paper form into a new database. The system rejects the entry.

(a) The NHS number is always 10 digits long. State the validation check that would have failed. (b) Describe a verification method the clerk could use to ensure they enter the number correctly on the second attempt.

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(a) Validation Check: A length check. The number entered, 1234567890, has 10 digits. However, the spaces mean the input string 123 456 7890 has a length of 12 characters. A strict length check expecting exactly 10 characters would fail. Alternatively, a format check expecting 10 numeric digits (NNNNNNNNNN) would also fail due to the spaces.

(b) Verification Method: The clerk could use a visual check. After typing the number 1234567890 without spaces, they would carefully compare the digits on the screen with the digits on the original paper form to ensure they match perfectly before submitting. Alternatively, the system could be designed for double entry, where it prompts the clerk to type the 10-digit number a second time and compares the two entries.

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