Chapter 1: Data Validation & Verification

Chapter 1: Data Validation & Verification

1. Validation

   • checks to reduce errors by restricting the data someone can enter
   • makes sure data is sensible

2. Verification

   • checks that data entered matches the data source
   • ensures data is entered correctly

3. Potential errors

   • customer may write down the wrong data in feedback forms
     • solution: use tick boxes or drop down lists to limit the possible choices
   • copying down information wrongly (transcription error)
     • solution: data verification such as visually checking
   • someone put their d.o.b as 30/02/1995 or ordered 1.5 pairs of shoes
     • solution: data validation to check that data is sensible

4. Types of validation

   • Range check
     • checks numerical data lies within a certain range
       • e.g. the range for the month of a date would be 1-12
   • Presence check
     • checks essential data is present
       • e.g. if you order something online you must enter your address
   • Format check
     • checks that data is laid out in an agreed way
       • e.g. the date is written in the format dd/mm/yyyy
   • Check digit
     • calculated the digits of a number to form an extra digit on the end. Then the computer checks the calculation
       • e.g. in a barcode, so that the user does not make a transposition error
   • Batch/Hash total
     • batch total is a number calculated at the start of transmission of a batch of data. At the end of transmission the calculation is repeated. These 2 results are then compared
       • a hash total os a batch total that has no meaning, e.g. the sum of people's telephone numbers

5. Types of verification

   • Visual check
     • compares the source of data and transcribed data by eye
   • Double keying
     • data is entered in twice to check it is entered correctly
   • Parity check
     • data is transmitted as a series of binary numbers, which are sets of 0s and 1s (these are known as 'bit's)
     • A parity bit is an extra bit that is added to the end of each binary number

6. Errors

   • omission error
     • leaving data out
   • transposition error
     • typing numbers in the wrong order
   • transmission error
     • caused by corruption of data