Beware the humble postcode, it tells me more about you than you think
Firstly, if a respondent provides their postcode for research purposes the researcher is able to ‘map’ that individual geographically. This could end up being a literal visual map, or the postcode could also be used to place the respondent relative to factors of relevance to the client (i.e. distance from planned advertising, or drivetime from a retailer).
The other thing is that a lot of interesting useful comprehensive statistics are available at postcode level. This means that if a respondent provides their postcode for research purposes, other data could then be appended to the survey using the postcode as a kind of anchor or link between data sets. Most often I have seen this done for a rural/urban classification, or a lifestyle classification – and when these are linked the appended data essentially becomes part of that individual’s set of answers. This is handy for all concerned because it saves the respondent being asked a huge swathe of questions to get to the same outcome. I wouldn’t need to ask you to give me a subjective categorisation of how rural your area is (could you?), or even what your income is or how many cars you have or what newspapers you read, because your postcode links me to ‘best guess’ responses to these questions.
As a researcher I’m always keen to collect postcodes for all of these reasons. But, I think it is important for me to advise you to think carefully about who you give your postcode information away to. It seems so innocuous (or does it seem creepy now you know what it tells me about you?) but in fact your postcode could also be a personal identifier meaning someone could use it to know things about you without your knowledge or consent. If you live in a rural area, your full postcode may be an identifier in itself. Someone could use it to find your home. In any area, your postcode narrows you down to a street or about 40 people, so may be an identifier when combined with other information you have provided alongside it such as gender or sexual orientation or which magazines you subscribe to. So if you are filling in a questionnaire-style form, in theory someone could look at your answers and know who you and where you live even if you have not provided your name or street address.
If you are taking part in a legitimate research project, no problem. Personal data is protected so that means it will be stored properly and will not be passed on or used for non-research purposes without your explicit consent. And, in fact, a legitimate researcher is forbidden from even pulling off a list of full postcodes, separating them from any other responses, and giving them to their client.
Can I send my client full respondent postcodes?: It depends on the respondent’s address. If they live in a rural area where there may be only a few homes in the area you could only give the first set of characters of the postcode. This is because these reference the area, anything more provides information on the particular sector where the home is situated and it is possible in rural areas for there to be only one home in a sector, and thus a respondent may be identified. If the home is situated in a town or city then it would be possible to provide the first set of characters plus one from the second set of characters. (Market Research Society FAQ)
I’m all for handing your postcode over for legitimate research purposes. It makes for richer data and keeps questionnaires short, which I approve of. However, do take care with who you give your postcode to. You should treat your postcode in the same way that you treat any other personal information such as your name or street address or phone number or email address.