Question about Carelessness

These types of errors can be hard to eliminate.  I would suggest doing some research on Mistake Proofing. 
It sounds like your problems are software / computer related.  If that is the case one option is to code as much logic into the data entry process as possible.  Have the computer do as much “look-up” and “data population” as possible so you do not have to rely on the operators to get it right.  Automation and simple tools or templates that make it easy for people to do the job right are the key.
We have had luck using different colors on the screen, or flashing text to prompt operators.  You can also program the key strokes to force some data to be entered before moving on.
I hope some of those ideas help – M

If your process is like most trainsactional ones then there are a lot of opportunities for mistakes.  In my experience processes like this suffer from “rolled through put yield” (RTY) issues and as such just applying Poke-Yoke to each step will net get you the results that you need.  A few years ago at a mortgage processor we applied Lean and drove the process from 42 days down to 13 minutes and in doing so cut out a lot of the process and dramatically improved quality.  So I’d suggest that applying Lean in your example may be the fastest way of driving improvements.  I’d certainly apply Poke-Yoke to the leaned out process – it’s just that you have to apply less of it in a Lean environment.
regards,
Adam

It seems you are entering data manually and everytime it is different so hard coding is not possible? What is data entry process – does the operator enter the new information from some hardcopy form? If that is the case, the only best option you have is to get the entered information reverified by another person.
To make a long story short, in one company we cut down entry time from 30 minutes to less than a minute.