OECD takes all its data for EU countries, Iceland, Norway, Switzerland and Turkey from Eurostat. The data are collected by national agencies in Labour Force Surveys and are processed centrally by Eurostat. The European Union Labour Force Survey is the final product.
Although Eurostat generally follows ILO's definitions, and records the same set of characteristics in each country, the survey methods differ between countries, sometimes significantly. You can find detailed outlines of all survey methods in Labour force survey in the EU, candidate and EFTA countries - Main characteristics of national surveys, 2010 (2012 edition). The outline for Sweden's survey methodology is very thorough, but also too large to quote here.
As for disability, generally speaking disabled people that satisfy ILO's criteria for "employed person" are counted in the employment rate. The more current data I could find for Sweden are from 2008's ANED Report on the employment of disabled people in European countries:
More than 900,000 persons in Sweden aged sixteen to sixty four have some form of disability (13% of the total population). More than half a million of these persons regard their ability to work as being reduced. A larger percentage of women than men report some form of disability. There are also more women than men among the disabled population who regard their abilities to work as being reduced. The most common disabilities are motor disabilities and asthma or allergies or some other form of hypersensitivity. There has not been any increase in any type of disability since 2006. Nearly half of disabled people are aged fifty to sixty four and more than half of those have a reduced ability to work.
The level of education is lower among the disabled than among the population as a whole. Post secondary education among the general population is 33%; among disabled persons with reduced ability to work it is 21%.
In 2008, 66% of disabled persons were in the labour force (of these, 55% has a reduced ability to work) compared to 81% for non-disabled persons. There has been an increasing tendency towards distance from labour force participation since 2006 between the disabled and the non disabled population.
The percentage of employed persons among the disabled is 62% and (50% among disabled persons with reduced ability to work) compared to 75% for non-disabled persons. The corresponding figures for unemployment are: 6.5%, 9.1 and 4.9% respectively.
