Marga Hoogendoorn

57 the observer during the entire shift. A longer-term patient could theoretically be observed on different dates during different shifts and therefore could possibly be followed during more than one measured shift. The measurements took place on different days of ICU admission (e.g. first ICU admission day through to last ICU admission day) and with different types of nurses (registered and student nurses). We randomly selected nurses who took care of patients that were expected to stay during the whole shift in order to measure as many nursing activities as possible. Observers were researchers CM and MH and ten student nurses. The students were trained in performing time-and-motion measurements by oral and written instructions and one day of measuring together with one of the researchers. The observers used an in-house developed web application to record start and stop times of each performed nursing activity. The application included all activities occurring in the NAS (appendix 3). If two nurses were simultaneously performing nursing activities for the same patient, this was also registered by pressing the ‘two nurses button’ and multiplying this time by two in the analysis. When two different activities were carried out by two nurses, these activities could be measured simultaneously. Measurements were conducted between 1 November 2016 and 1 October 2017. Participation of the hospitals was on a voluntary basis. Seven hospitals were willing to participate. Data were processed anonymously. Ethical approval The Institutional Research Board of the Amsterdam University Medical Centre reviewed the research proposal and waived the need for informed consent (IRB protocol W17_366). Data analysis Nursing activities that occurred less than ten times in the total dataset were excluded from the analysis. Most NAS items have a fixed number of NAS points, but some items have different categories corresponding to different numbers of NAS points depending on the duration of that activity (e.g. bedside with hourly vital signs, bedside for two hours or more, or four hours or more). For these duration-dependent activities, we first used the measured time for that activity to assign the correct number of points. For example, a nurse performed hygiene procedures on a patient for 1.2 hours during a shift, according to our time measurements. This NAS item has three categories: performing hygiene procedures for less than two hours, for more than two hours, or for more than four hours. In the above-mentioned example, the activity took 1.2 hours and would therefore be assigned to the category for less than two hours, which corresponds to 4.1 NAS points. To validate the NAS, we first converted the originally assigned NAS points per activity into time. Based on Miranda et al 7 . 100 NAS points correspond to 100% of care time provided by one nurse