Question on occupation

I have just spent a laborious few hours trying to categorise the occupations of several thousand operated patients as manual or non-manual. There is a fair amount of literature relating the incidence of CTS and the outcome of treatment to occupation and for the most part it suggests that manual work is associated with more CTS and worse treatment outcomes. At present we ask people to give their occupation in free text but I would like users to add their own assessment of whether theirs is a 'manual' or 'non-manual' occupation. How do people feel such a question should be phrased?

At present I would be thinking of something like...

Do you consider that your occupation is 'manual' - ie predominantly involved with heavy tasks with the hands (building trades, assembly lines, manufacturing, cooking, driving, cleaning) or 'non-manual' (administration/secretarial, managerial, professional, retail)?

Some occupations are rather tricky - people working in supermarkets may be mainly shelf stacking and doing warehouse work - which I would tend to classify as manual, whereas others may spend their day on the checkouts, which is less so.

I am not sure what we should do with 'housewife/homemaker' either - manual, non-manual or a separate category?

Any thougts from the public would be welcome before we actually add anything else to the questionnaire JB