# dimensional analysis vs. ratio/proportion

1. I did a search but couldn't find a discussion on this exact subject, so here goes:

Is one method truly better than the other or is it (like most things) a matter of personal preference? I've been messin' around with both using Pickar's "Dosage Calculations" for ratio/proportion and Medication Math for Nursing Students, http://www.alysion.org/dimensional/analysis.htm#guide, for DA.

From my perspective, RT is way more comfortable for me than DA. I get so confused with how to line up the pieces of DA that I simply give up on it and just go to the formulas of RT which yields the answers quickly (and to me simply).

Hmmm, I guess my real question is, what method will my school want me to use? The book we're supposed to get is Calculate with Confidence (which is on its way now) that includes instruction in both methods .

I'm figuring that if I consistently get the right answers, the instructor won't really care what method I use....
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3. you should, of course, use the method your school wants you to use. most instructors should be showing students both methods. although i will show students how to do problems by dimensional analysis on the forums, in practice, i actually use formulas because they are faster and because i have a very good understanding of what i am doing. i also work with these formulas every day at work. about the only exception is when calculations involve iv drips, conversion factors and getting into micrograms of medications. then, i have to use da to make sure i am absolutely accurate.

here is a link to a chemistry teacher's explanation of dimensional analysis put into terms other than chemistry (baseball, i do believe). it's an interactive little video with some animation that helps to break down and explain how dimensional analysis is set up and works.

http://www.wwnorton.com/chemistry/tutorials/ch1.htm - click on "1.4 dimensional analysis". it is an interactive program that explains da using animation rather than video in what i thought were very simple terms. also includes several problems you can try your hand at which are not chemistry related but utilize the concepts of da.
4. I always go with dimensional analysis. I guess because it make mores "sense" to me after using it so much in chemistry during pre-reqs. I'm not great with math to begin with. With DA, I feel like there is less to remember and my memory isn't great. I like one concept that works for everything and using formulas feels like every calculation is different...

However, it very well might take longer.
5. I have spent many years teaching new nurses in hospital orientation. I find that the people who rely on Dimensional Analysis (DA) struggle a lot more with real life situations than do the new grads who use the Ration and Proportion (RP) method.

The reason seems to be that many people who rely on DA never really understand the fundamental relationships among the various pieces of information within the situation. They do fine with common problems that present themselves in standard, common ways -- but get all confused when a real-life situation doesn't "fit" the usual pattern: they can't improvise and adapt well because they don't fully grasp the underllying relationships.

The people who use RP are usually better able to improvise within a new and different complex situation that involves multiple steps. They break the complexity down to its component parts and start working out the ratios one at a time, progressing toward a solution step by step -- even if they don't "see the solution" at the beginning. They start with the fundamental relationships (proportions) among the items involved in the situation and build from there.

In real-life practice situations, the ability to figure things out that don't look familiar is very important -- and is often the factor that differentiates the expert from the novice. The RP folks seem to be better at this than the DA people in my considerable experience. However, either will get you through school because student level problems are not at the expert level of complexity.

llg
6. Dimensional analysis (and thank goodness we are not asked to use this)...confuses the life out of me. I love ratio/proportion and I also LOVE Pickars doseage calculations book. If someone on this board posts a calc question and the answers all come in using DA...I don't even bother reading the answers because it makes zippo sense to me. Ratio/Prop or Dose avail/dose on hand for me allllll the way!!
7. I teach pharmcology and I present both methods to the students so they can pick which one is easier for them to comprehend and use. Personally I like dimensional analysis - I have colleagues that would choke on a football before they would try anything other than R/P. As long as you get the right answer, and know how you got it, that would be okay with me.
8. I always knew how to do ratio and proportion, but it just seems like so much extra work, and easier to make a mistake. i went out and bought the DA book by Anna curren and i love this method. Its so easy to learn and i think safer to calculate dosages. I did not know anything about how to calculate dosages, and thats scared me, so i wanted to learn before i started school next month and a few eeks ago i went and bought the book(DA for Meds) and in that little bit of time i learned how to calculate dosages.. i can even figure out body surface area, titrate iv, flow rate etc. i think DA is the best, our school i think is going to show us all the ways to do it and we pick the way that we think is easier, i am definitely going to stick with DA
Last edit by tookewlandy on Aug 17, '06
9. Quote from llg
I have spent many years teaching new nurses in hospital orientation. I find that the people who rely on Dimensional Analysis (DA) struggle a lot more with real life situations than do the new grads who use the Ration and Proportion (RP) method.

The reason seems to be that many people who rely on DA never really understand the fundamental relationships among the various pieces of information within the situation. They do fine with common problems that present themselves in standard, common ways -- but get all confused when a real-life situation doesn't "fit" the usual pattern: they can't improvise and adapt well because they don't fully grasp the underllying relationships.

The people who use RP are usually better able to improvise within a new and different complex situation that involves multiple steps. They break the complexity down to its component parts and start working out the ratios one at a time, progressing toward a solution step by step -- even if they don't "see the solution" at the beginning. They start with the fundamental relationships (proportions) among the items involved in the situation and build from there.

In real-life practice situations, the ability to figure things out that don't look familiar is very important -- and is often the factor that differentiates the expert from the novice. The RP folks seem to be better at this than the DA people in my considerable experience. However, either will get you through school because student level problems are not at the expert level of complexity.

llg
Have you been dipping into the spiritus fermenti a little early today? Just kidding! That was too scholarly, even for me! But, I think I agree with what you said!
10. You should forget ratio/proportion..That thing is confusing...
11. Do whatever is easier for you. I find that ratio and proportion is much quicker and I was accustomed to dimensional analysis before I studied med math.
12. Here is a simple way to figure out a medication problems in division:

Desired
--------
Have

That is desired divided by have..Very simple!!
Last edit by Bala Shark on Aug 17, '06
13. thanks bala shark, I thought I was the stupidest person on earth. I graduated in May and that was the only was I was taught to calculate, desired/have. ratio and proprotion was mentioned but the instuctor was very uncomfortable using that method. I have no idea what DA is. I used the book, calculate with confidence, in school. It is a great book and uses desire/have. In clinical and on tests I never had any difficulty calculating dosages using this method.
14. ahhh, so if I divide what I desire by what I have, I'll know what I need. Yeesh, the story of my life.....