The care of sick and elderly people is personnel-intensive and must be carried out primarily by formally trained persons. This is an area where Germany with its shrinking and ageing population will soon reach its limits . In this paper, we focus on nursing professions as defined by the German Classification of Occupation 1992 (KldB 92). This includes nurses and midwives (Category 853, KldB 92), auxiliary nurses (Category 854) and geriatric nurses (Category 864). In Germany, graduated nurses or geriatric nurses have 3 years of formal training and are able to conduct all nursing duties. In contrast, an auxiliary (geriatric) nurse has only a one- to two-year training programme and thus, is given a restricted list of tasks, compared to nurses and midwives and geriatric nurses . Unfortunately, the KldB 92 does not differentiate between geriatric and auxiliary geriatric nurses. Therefore, all individuals with a vocational training of at least one year duration within these three groups will be referred to as formally trained nursing professionals in the following. It is important to remember that vocational training for graduate nurses and graduate geriatric nurses is highly regulated in Germany. However, since the curricula for these two occupations are similar, geriatric nurses can, in practice, be employed as regular nurses and vice versa. Nonetheless, this always depends on the particular duties to be performed.
The situation is different at the level of auxiliary (geriatric) nurses. Similar, for example, to the US  or UK , in Germany it is also possible for an individual to perform certain nursing duties such as performed by (geriatric) nursing assistants after having received a few weeks or months of corresponding training. In the following, such individuals who have received less than one year of training will be referred to as semi-skilled labour nurses. As for other occupational classifications [4, 5], the KldB 92 classifies a set of tasks without a strong distinction between the different formal qualifications required to fulfil those tasks. This means that (geriatric) nursing assistants with less than one year of training are classified as being employed as auxiliary nurses (category 854) or geriatric nurses (category 864) (see endnotes for more detailed information).
Forecasting models for the supply of and demand for nurses usually concentrate only on the inflow of graduates and/or immigrants from other countries and on the attrition and retirement rates for graduate nurses . However, semi-skilled nursing professionals can improve organizational efficiency  and will be needed to meet the increasing demand for care. In Germany, the number of auxiliary nurses has steadily increased from 209 000 persons in 2000 to 269 000 persons in 2010 . Since the number of employed semi-skilled labour nurses is mainly contained in the number of auxiliary nurses, these developments indicate that semi-skilled labour is becoming increasingly important for meeting the demand for nurses. Consequently, in order to forecast the supply of nursing professionals, we have to examine both the occupational outflows of formally trained nursing professionals  and inflows of persons with less than one year of training, that is, occupational mobility into and out of nursing professions (Additional file 1).
For this paper, we analyzed occupational flexibility and different employment structures (full-time, part-time and number of hours worked per week) to identify ways to increase the supply of nursing professionals. We then contrasted our different supply scenarios with two demand scenarios of nursing professionals (nurses and midwives, auxiliary nurses and geriatric nurses) developed by the German Federal Statistical Office .