On 3 Aug 2000, DavidS9307 wrote:
> I would like to collect data in a school on a survey form where the
> respondents enter only a code number to identify themselves. I would
> like the code number to be something that the participants will be able
> to remember for follow-up data collection in the near future, but I
> would also like to protect against identifying the participant even if
> the forms and coding scheme were disclosed, so I don't want to use
> birthdates, names of relatives, or SSNs.
Surely you also want the codes to be unique, so that your follow-up
analyses do not confuse Maxine with Raymond simply because they happened
to produce the same code.
> I had been thinking of using some number not generally known to anyone
> other than the participant, such as the last digit of their locker
> number at the school,
"Last digit"? You ARE planning to have a sample
size larger than ten, aren't you?
> to disguise a universal identifier by adding it to each of the last
> four digits of the SSN, but that seems rather clumsy.
I take it that "adding" refers to doing arithmetic, not to merely
appending a common value (which would not disguise things much!).
But there is still the question of uniqueness: can you be guaranteed
that there are no duplicates of the last 4 digits? I doubt it.
> Does anyone have a suggestion for a good coding scheme?
> Thanks to all for any recommendations.
Generate a set of, say, 3- or 4-digit numbers. Print each on one side
of a card. Shuffle the cards. Take the cards (or a sufficiently large
subset of them) into the classroom where you introduce the survey to the
participants. Visibly shuffle them again, and deal them (face down), or
have assistants deal them, one to a customer. Explain why you need the
numbers, ask them to memorize their own code (and/or squirrel the card
away in a safe place where they can find it later), and write it in the
space provided for the purpose on the survey response forms.
If you are dealing with classroom-sized groups of participants (i.e.,
fewer than 52 persons per subgroup) you could use ordinary playing cards
plus a precoded identifier for the subgroup. Makes a 2-character
identifier, possibly easier to remember than an arbitrary 3- or 4-digit
number (though people seem to do all right with PINs for their ATM
cards): AH for ace of hearts, 3S for trey of spades, etc. And you'd
have to ask them to remember the subgroup identifier as well, but perhaps
you could use a single alphabetic character for that (or a number if
there are ten or fewer groups).
(Make sure you remove the jokers etc. before you shuffle & deal!)
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Donald F. Burrill [EMAIL PROTECTED]
348 Hyde Hall, Plymouth State College, [EMAIL PROTECTED]
MSC #29, Plymouth, NH 03264 603-535-2597
184 Nashua Road, Bedford, NH 03110 603-471-7128
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