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Both issues are hard to measure statistically because very few will pay attention to it, and if it ever happens, the persons involved will quickly correct it and try to hide it from others.

However, there is technology to measure reliability (reproducibility and distortion) of barcode reading, such as this.

Are there any studies comparing the relative frequency of barcode misreads and cashiers giving out the wrong change?

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    Barcodes encode product-id not price tag. Usually if a barcode is misread then a different product appears on the reading machine. From my experience, the only time I saw a misread barcode the machine showed 93 tones of cheese. – Alexandru May 23 '11 at 14:43
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    @Alexandru: in many cases Barcode also encodes the quantity of the item (especially items sold in weight); but you're right, in most cases misread barcode would give a totally off data that people would likely immediately notice. – Lie Ryan May 23 '11 at 15:10
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    Note that the most common barcodes include some sort of checksum (e.g. EAN has a check digit), so a misread would in most cases produce an invalid code. – Piskvor May 23 '11 at 17:21
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    Sacnning errors must come in at least three sorts: (1) mis-scan, but as Piskvor says there is some protection against that (2) mis-labeling (wrong bar code on the product) which should be rare with commercial products but has been used to steel things (by covering the barcode with that for a much cheaper item) and (3) data-entry error in the database that backs up the scanner (which is probably the case with Alexandru's story). – dmckee May 23 '11 at 17:39
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    Due to the check digit, a barcode would have to be very badly misread to produce a number (most misreads simply produce an error output). Further, that number has to correspond to a real item in the database, and UPC codes in use today for products are not fully packed - you can't guarantee that by changing one number to another, you'll get a valid product, nevermind a valid product that this store actually carries and has a database entry for. All these factors combined mean that there's a very, very, very tiny chance of this happening. – Adam Davis Aug 8 '11 at 19:53
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The question is confusing two separate issues:

Cashiers can give wrong change independently of whether bar-codes or price-tags are used.

Bar-codes are intended to lead to fewer data-entry errors and faster data-entry than price-tags.

Here is a quote from the Bar-Code FAQ at adams1.com.

What are the advantages and disadvantages of barcode? There are two basic advantages to barcode over manual data entry: Speed, and Accuracy. For 12 characters of data, keyboard entry takes 6 seconds. Scanning a 12 character barcode takes .3 seconds. The error rate for typing is one substitution error in every 300 characters types. Error rated for barcode range from 1 substitution error in every 15,000 to 36 trillion characters scanned (depending on the type of barcode). [...] The only disadvantage is that data must be coded in the barcode.
  • Note that the error rate quoted here is that for mis-scanning (and I suspect accounts for the error correction intrinsic in the code). It leaves open the possibility of errors in a database backing the system (because most stores don't code the price in the barcode, but rather a product ID for use by the inventory control system). – dmckee May 23 '11 at 17:41
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    @dmckee, very true, which is why I was sure to include that last sentence in the quote. For fairness, the corresponding error - wrongly printed price-tags - should also be included in the mix. – Oddthinking May 24 '11 at 0:11

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