Clinical effectiveness and patient safety are at risk if inaccurate drug doses are administered. This study revealed gaps in basic mathematical skills
Miriam McMullan, PhD, MSc, BSc, is lecturer, Faculty of Health, University of Plymouth.
McMullan M (2010) Exploring the numeracy skills of nurses and students when performing drug calculations. Nursing Times; 106: 34, 10-12.
Background It is essential for patient safety that nurses are able to competently perform numerical and drug calculations.
Aim This study aimed to investigate and compare the numerical and drug calculating abilities of second year student nurses and registered nurses attending a non-medical prescribing programme (McMullan et al, 2010).
Method All participants were given validated numerical and drug calculation tests. Data collection took place in 2006.
Results Some 55% of students and 45% of nurses failed the numeracy test, while 92% and 89% respectively failed the drug calculation test (at a pass level of 60%). Both students and nurses were more able to perform calculations for solids, oral liquids and injections than calculations for drug percentages, drip and infusion rates. Nurses were more able than students to perform basic numerical calculations and calculations for solids, oral liquids and injections.
Conclusion To prevent deskilling and ensure patient safety, nurses should regularly practise and refresh all types of drug calculations with self testing. Time should be set aside in university curricula to enable student nurses to learn how to perform basic numerical and drug calculations. During clinical placements, this learning should be reinforced through regular nursing practice and assessment.
Keywords Numerical skills, drug calculations, patient safety
- This article has been double-blind peer reviewed
- To prevent deskilling, nurses should practise and refresh all types of drug calculations, with regular (self) testing of their ability.
- Time should be set aside in curricula for student nurses to learn how to perform basic numerical and drug calculations.
- During clinical placements, students’ learning should be reinforced through regular assessment of their calculation skills.
In healthcare, drug calculation errors are a serious problem and have become a national concern. Studies have shown that 30-40% of medication administration errors are due to drug calculation errors (Schulmeister, 1999) and these figures may under represent the extent of the problem (Weeks et al, 2000).
Basic mathematical skills are essential for drug calculations, yet many international studies have shown that both student nurses and registered nurses struggle with basic calculations. For example, Hutton (1998) found that 80% of 231 first year student nurses scored less than 75% on a 50 item numeracy test. Learner (2006) reported that the Nursing and Midwifery Council was extremely concerned following reports in a newspaper that a third of newly registered nurses (13 out of 40) failed a basic numeracy test (with a 60% pass level) set as part of a new selection process.
Clearly, both clinical effectiveness and patient safety are at risk if inaccurate drug doses are administered because of poor numerical skills and/or poor drug calculation skills (National Patient Safety Agency, 2009).
This study aimed to examine and compare the numerical and drug calculation skills of student nurses and registered nurses.
The research was carried out in a regional UK university and full ethical approval was granted. Participants were 229 second year student nurses and 44 registered nurses attending a non-medical prescribing programme.
They were given a numerical test and a drug calculation test to complete but were not allowed to use calculators, as the NMC recommends (2004).
The numerical test consisted of 15 questions covering the main key calculation skills such as addition, subtraction, multiplication, division, fractions, decimals, percentages and conversions.
The drug calculation test consisted of 20 questions covering the main types of drug calculations such as dosage calculations for solid and liquid oral medication and injections, percentage solutions and intravenous fluids (Table 1). The data was statistically analysed using SPSS. Further details on the method are available in McMullan et al (2010).
Results and discussion
In the numerical ability test, 55% of student nurses and 45% of registered nurses achieved a score of less than 60% (Table 2). These results were very similar to those found in the UK and other countries such as the US, Australia and the Netherlands (for example, Brown, 2002).
One possible explanation could be the use of, and dependence on, calculators. Although calculators can help with basic arithmetic and reduce the number of computational (mathematical) errors made, they cannot tell users which data to input and how to interpret the results.
Studies have found they increase the number of conceptual errors (inability to set up the mathematical calculation needed) by giving users a false sense of security (Shockley et al, 1989). By using and relying on calculators all the time, even for performing simple sums, users become deskilled in mental arithmetic. As a result, they start to lose their feeling for what would be considered a reasonable answer. This may lead to errors going unnoticed.
Although 45% of nurses also performed poorly in the numerical ability test by achieving a score of 60% or less, they were still better at performing basic numeracy than students.
We can only speculate why this might be the case; one possible factor could be age. The nurses were significantly older than students and, in this study, participants aged 35 and over were more competent at performing numerical calculations than their younger counterparts. A possible reason why older participants performed better could be the type of mathematical education they received during their formative school years and, in particular, the absence of calculators during this period. Older participants, who did not use calculators when they were at primary and secondary school, obtained a great deal of practice in mental arithmetic.
Younger participants had been taught mental arithmetic at primary school without calculators, then started to rely increasingly on them, even for simple calculations, during secondary education. This increased reliance on calculator could have led them to lose proficiency in mental arithmetic and in their ability to determine what would be considered a reasonable answer.
This problem with poor numerical ability is not only seen with student nurses but has also been reported with students following other university courses, such as engineering, pharmacy, psychology and medicine (for example, Sheridan and Pignone, 2002).
Drug calculation ability test
Both students’ and nurses’ results in the drug calculation ability test were poor, with 92% and 89% respectively obtaining a mark of less than 60% (Table 2).
Similar results have been found in other studies in the UK and abroad. For example, Jukes and Gilchrist (2006) found that, on a 10 item drug calculation test, 64% of 37 second year student nurses achieved a score of less than 70%.
Closer analysis of the results showed a clear division in the scores according to the types of drug calculations that needed to be performed. In this study, both students and registered nurses were much better at performing calculations for solids, oral liquids and injections than drug percentages and infusion rates (Table 2).
In addition, although there was no statistically significant difference between students and nurses in their ability to perform drug percentage and infusion rate calculations, the latter were significantly more able to perform calculations for solids, oral liquids and injections.
A possible explanation is that calculations for drug percentages and infusion rates are generally conceptually more difficult than those for solids, oral liquids and injections. In our study, both students and registered nurses struggled with the conceptual nature of drug percentage and infusion rate calculations before getting to the numerical element of the task.
Calculations for solids, oral liquids and injections were conceptually easier and the mistakes made here were mainly numerical errors. As registered nurses were significantly better at performing arithmetic, they made fewer errors and therefore had fewer problems with these calculations than student nurses.
The question remains as to why registered nurses had problems performing (and conceptualising) the drug percentage and infusion rate calculations. Studies have shown that registered nurses tend to become “rusty” in performing calculations that they do not need to do on a daily basis in their work (Preston, 2004).
In this study, the majority of registered nurses worked mainly in primary care and therefore had no need to perform many infusion rate calculations in their daily work. As a result, they became rusty in these types of calculations and, without practice, lost their expertise.
In addition, nurses can become deskilled because they use technology that performs calculations for them in clinical areas, such as intravenous pumps. However, this technology might not always be available and, even if it is, to rely unquestionably on it could be dangerous. Nurses also have to input the data and interpret the results. However, if they are unable to do this, due to a lack of drug calculation skills and experience, mistakes may go unnoticed, placing patients’ lives at risk.
To obtain proficiency in performing numerical and drug calculations and to develop a “feeling” for what could be considered a “reasonable” answer, student nurses should initially learn to perform calculations without calculators.
Although calculators may be useful in checking answers, it is important that students develop the underlying mathematical knowledge and skill to perform drug calculations and to be able to interpret the result accurately. To ensure this, regular practice and support from educational and clinical staff is essential.
Time should therefore be set aside in university curricula for students to learn how to perform basic numerical and drug calculations (NMC, 2007) and, as programmes tend to be assessment led (McMullan et al, 2003), to strengthen this skill through assessment before students leave for clinical placements. Subsequently, during clinical placements, this learning should be further reinforced through regular practice and assessment (NMC, 2007).
The registered nurses were a self selected sample working mainly in primary care settings.
To prevent deskilling and ensure patient safety, it is important that registered nurses regularly practise and refresh all types of drug calculations with self testing.
For student nurses, time should be set aside in university curricula to enable them to learn how to perform basic numerical
and drug calculations. This learning should be further reinforced through regular nursing practice and assessment in clinical practice.
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