Some kind of curse…

November 4th, 2005

My analytical chem lab frustrates me.

We get marks for accuracy and precision, and despite my best efforts, I have FAILED this criterion in more than half of my labs. Each time with a 9/20. It’s some kind of curse, I swear. I’m always accurate–always–but my precision could use a little work. It’s getting to the point where it’s a bit ridiculous, really. In this last lab, I had a 99.42% correlation between my data and the best fit line. That was worth a big, fat zero. (My Ka value earned me a 9.)

My accuracy and precision grades are worth 12% of my lab mark, which is ultimately 3% of my overall mark in the course, but keep in mind: I have to pass the lab to pass the course. =_=

I mean, in one lab my prof couldn’t even TELL me what went wrong. v_v And the other one didn’t count, and I overshot my first titration, so I really didn’t care. ARRGH. I have two labs left to make this up, and … yeah.

I’m NOT a bad chemist otherwise in that lab; it’s not like the rest of my accuracy/precision grades are marginal pass marks. The other ones (if I remember correctly) are something like 16, 19, and 17.5. I mean… if my marks were consistently low there would be a problem, but since they’re not, I just really can’t understand what’s going on.

Well, scratch analytical chemistry off my specializations list. :tongue:

This entry was posted on Friday, November 4th, 2005 at 7:37 pm and is filed under general. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.

6 Responses to “Some kind of curse…”

Anthony Says:

What’s the difference between accuracy and precision?

November 5th, 2005 at 3:31 pm

Cat Says:

Accuracy is how close you end up to the right answer, “on average.”
Precision is how replicable your measurements are.

To use the hackneyed bullseye model:

If all my arrows are in the center, I have high accuracy and high precision.
If all my arrows are clustered off to one side, I have high precision but low accuracy.
If my arrows are mostly in the general area of the center, but not clustered close together, I have high accuracy but low precision (this is what I get in my labs, for whatever reason.)
If my arrows are all over the target, maybe with a few clusters here and there (not to mention a few misses), I have low accuracy and low precision.

November 5th, 2005 at 10:11 pm

Neale Says:

For the first time in my life I understand the difference. I’ve also never heard that metaphor before, so… more power to you!

November 5th, 2005 at 10:51 pm

Bobby Says:

If I remember correctly, the concepts of accuracy and precision are very similar to the ideas in psychology of validity and reliability.

November 6th, 2005 at 12:24 am

Anthony Says:

Very insightful.

November 6th, 2005 at 2:59 pm

Cat Says:

Oh, and for anybody who’s still confused, I present to you:

The Wikipedia article on Accuracy and precision.

November 6th, 2005 at 2:02 pm