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Beware the humble postcode, it tells me more about you than you think

September 8, 2015

2012-11-02Postcodes may seem like silly little administrative numbers and letters, but for a researcher they are a goldmine of useful information and a gateway to even more.

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.

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3 Comments leave one →
  1. Gill permalink
    November 2, 2015 7:59 pm

    Hi Ruth I was wondering if there is a piece of software that maps postcode data? I wanted to map location of respondents for a recent project and couldn’t work out the most efficient way to analyse the data… Also do you find that young people know their postcode or do you just tend to ask about town? Thanks!

    • November 3, 2015 4:08 pm

      Hi Gill, agree it is difficult to know how to do anything useful with geographic data. A few ideas:
      – Where budget is limited I have simply counted/% geographic responses at a partial postcode level (i.e. EH1) or at a town level (i.e. EH) then turned it into a bar chart.
      Zeemaps is a pretty good way of quickly creating a literal map from a list of postcodes. You can load them all in from a spreadsheet and it costs about $20.
      – If resources permit it can be quite helpful to run the data against geosocial datasets such as ACORN or MOSAIC – I think you need to contact the providers of the datasets directly.
      – Big organisations have fancy systems for doing all this, and more – things like drivetimes from a venue or advertising point for example. I expect you can subcontract this from a field&tab agency.

      I’m not really sure about getting a postcode from young people, I guess it depends on their age and younger ones might not know their postcode. It might also be an ethical consideration whether young people can technically give consent / understand if it is OK to provide a postcode. Might be safest to stick with town?

      • Gill permalink
        November 3, 2015 4:18 pm

        That’s great, thanks for your response Ruth. Gives me a few things to look at! Gill

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