# Difference between all these stupid ISA words?

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#1
I'm really, really hoping someone can give some clarity here because we're doing the biology written ISA paper tomorrow and I just can't understand the difference between some of these words.

Accuracy and precision: I get that accuracy is about systematic error and precision is about resolution, but I don't know how to word them, at all. Neither does anyone else, apparently. According to my physics book (the only book I have containing ISA prep stuff):

"Accuracy is a measure of confidence in a measurement and is usually expressed as the uncertainty in the measurement."

And the next paragraph...

"The precision of the measurement is given by the uncertainty of the readings."

So... they're effectively the exact same thing?

I'm also a bit confused about the difference between reliability and repeatability. As far as I understand they both just mean the ability to repeat an experiment and achieve the same results.

If anyone can help with this, it'd be much appreciated. I've looked around for resources, but other than glossaries with more vague and confused definitions there's not much.
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7 years ago
#2
What title is the ISA you're doing tomorrow?

I don't really get Accuracy / Precision either but maybe I can help with reliability / repeatability.

Repeatability is how many times the experiment is repeated in order to generate a mean result to obtain a reliable result.

Reliability is about the confidence that the result that is produced is a value that is determined by the independent variable and experiment.
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#3
Thanks, that clears things up a bit.

I'm not sure of the exact title, but it's about osmosis in potatoes. We've done the practical, just doing the written paper.
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7 years ago
#4
"The effect of concentration of blackcurrant squash on osmosis in potato cylinders"

This is the title. When are you taking the written paper?
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#5
Ah yeah, that's it. Probably taking it at 10:00, but I'm hoping we'll be able to do it at lunch time or something instead to get a bit of extra study time.
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7 years ago
#6
(Original post by Danzee)
What title is the ISA you're doing tomorrow?

I don't really get Accuracy / Precision either but maybe I can help with reliability / repeatability.

Repeatability is how many times the experiment is repeated in order to generate a mean result to obtain a reliable result.

Reliability is about the confidence that the result that is produced is a value that is determined by the independent variable and experiment.
Dude, reliability isn't on the specification anymore. I'm pretty sure they've phased it out and replaced it with reproducibility.
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7 years ago
#7
Oh... I was still under the impression of still using reliability. Do you have a specification you can reference for the definition of reproducibility?
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7 years ago
#8
From what I understand;

Accuracy is how close to the true value a result is, for example, calibrated equipment would give an accurate result. Or when measuring gravity, getting an acceleration value close to 9.81m/s^2 is accurate.

Precision is the smallest increment on the measuring device, for example, a ruler is precise to 1mm (smallest measuring increment). Getting the same value for gravity of 9.81m/s^2 would be less precise than if the measurements could measure to 1 more decimal place I.e 9.813 is more PRECISE

The results can still be precise if they're inaccurate and visa versa.

Hope this helps
Source: did ISA exams for A Level Physics but not sure how they apply to Biology

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7 years ago
#9
These terms are usually represented using a target.

Imagine lots of arrows evenly spread around, but close to the centre of the target. That's accuracy.

Now imagine lots of arrows very close together, almost touching one another, but all 20 cm below the target. That's precision.

Accuracy and precision would in this case be multiple arrows extremely close together, and in the centre of the target.

Let's say you do a titration using a molarity of solution 20% higher than it says on the label. You get identical titres for three titrations. Your results are precise but not accurate.

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7 years ago
#10
What exactly are you revising for this? I have this tomorrow too. They told me to revise water transport, and osmosis pretty much.
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7 years ago
#11
A method which gives similar results over and over again is said to have a high repeatability.

Reliability is related to the confidence you can have in your results. A feature of reliable methods is the use of blanks, primary standards, etc. and more fundamentally a sound chemistry theory behind it. In other words, a method which does not account for interferences or gives erratic results is unreliable.

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#12
Thanks for the answers, it's really helped clear things up. I had no idea that reliability stopped being used, we've been told to use it.

Gonna read over this again in the morning and hopefully it'll go alright. Except...

(Original post by Danny786)
What exactly are you revising for this? I have this tomorrow too. They told me to revise water transport, and osmosis pretty much.
I only did osmosis, I don't think we got told to revise water transport. But now you mention it, it seems really likely there'll be something about that in there. And it happens to be my worst topic.

Oh well, too late now. Good luck!
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7 years ago
#13
(Original post by sc756)
From what I understand;

Accuracy is how close to the true value a result is, for example, calibrated equipment would give an accurate result. Or when measuring gravity, getting an acceleration value close to 9.81m/s^2 is accurate.

Precision is the smallest increment on the measuring device, for example, a ruler is precise to 1mm (smallest measuring increment). Getting the same value for gravity of 9.81m/s^2 would be less precise than if the measurements could measure to 1 more decimal place I.e 9.813 is more PRECISE

The results can still be precise if they're inaccurate and visa versa.

Hope this helps
Source: did ISA exams for A Level Physics but not sure how they apply to Biology

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