Review the med-math test.

How to Minimize Mistakes

Anything we can do to reduce errors by even the smallest degree is worth doing. How we choose to write down a DA problem, for example, can make a difference. Should we just keep the answer unit in mind, circle it in the problem, or actually write it down? At best we will hit what we aim for, so we must be very clear about what we want, about the answer unit(s) we are aiming for. Reading the problem with the sole, focused purpose of determining the answer unit, then writing it down (least we forget or get confused later on) is an example of good technique.

You can be sloppy and still get the right answers most of the time, but eventually you'll blunder because of poor technique. You'll triumphantly, like me, write down "4.3 mL/min" as your answer forgetting that you were supposed to calculate "mL/hr" and all because you neglected to write down the answer units and compare them with your answer.

DA problems are often written in fraction form, even though they are factors and shouldn't be confused with fractions. Fractions cannot be inverted and remain correct, 2/3 is not equal to 3/2, while factors can be (3 tsp/1 tbs is equivalent to saying 1 tbs/3 tsp.

When it comes time to do the math, the first number can be overlooked, especially if you're using scratch paper with other problems on it, perhaps because it is visually different and not in line with other values. An error of omission is less likely using the following non-fraction format:

This format is more visually integrated, more bridge like, and is more appropriate for working with factors. It is also less confusing when doing amounts-per-body-weight-per-dose or day calculations. In this format, the horizontal bar means "divide," and vertical bars mean "multiply."

Occasionally a factor like "50 kg" will need to be divided rather than multiplied which could cause confusion or errors when doing the math if the division sign is not noticed when written in fraction form.

Since the first factor is normally multiplied, students might stumble if division is required and divide everything into 50, an error, instead of multiplying 250x50x1000, then dividing by 50 and 500. When written in factor form using bars, mistakes and confusion are minimized:

This is, then, another reason to avoid the fraction format.

Perhaps with the exception of conversion factors you have memorized, it is advisable to actually write down, in "math terms" or factor form anything given to you by the problem as well as any conversion factors you had to look up. Often the hardest part of a problem is translating fuzzy English phrasing into crisp math terms you can use.

Use abbreviations that are clear and label numbers fully. Using a degree symbol for hour instead of "hr" is an invitation to error. If the degree symbol is written a little too big it could be mistaken for a zero resulting in an order of magnitude error. When doing the math, the brain is looking for numbers and could see "10" where a "1" is meant:

Avoid "cc" and use "mL" instead as cc can look like zeros. Likewise don't use U for unit. Write 5 units insulin, and not 5U insulin, which could be mistaken for 50.

When writing numbers less than one, always start with a zero, so write 0.4 and not .4 as the point could be overlooked. When writing whole numbers omit writing a point zero to indicate that the measurement was made to the nearest tenth (or point zero zero to indicate an accuracy of plus or minus a hundreth) as you would in science lab. In med-math a hand written 5.0 could be mistaken for 50 if the point were over looked.

Another abbreviation to avoid is using Mu (m) for micro as in microgram ( m g). When handwritten, " m " can look like an "m" and so " m g" looks like "mg" which could lead to a three orders of magnitude error. The preferred abbreviation, then, is "mc" for "micro" as in "mcg" for "microgram."

If you were doing calculations involving milliliter volumes of three solutions, A, B, and C, then do not use "mL" alone without specifying "mL of what?" Your labels, then, would be in the form "23 mL A" or "3 mL C" and you would know to only cancel out "mL B" with "mL B." Whenever you label any number with a unit of measure, always be aware that you are dealing with grams of something or liters of something , and so on. It may therefore be helpful to label fully rather than minimally. Writing "25 mL NS" is much clearer than just "25 mL." In some problems, failure to fully label numbers can lead to serious confusion and error.


Errors may be unavoidable in absolute terms, but we can minimize the number of errors we make. A good understanding of dimensional analysis is our best defense against miscalculation errors. With practice all nursing students can acquire a high level of proficiency in doing medication math.

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