# Can anyone help my niece. I don’t know anything about chemistry ?

And an explanation as to why

### 8 Answers

- busterwasmycatLv 74 weeks agoBest Answer
Accuracy refers to how near to true value a measurement is. Precision refers to how repeatable a measurement is.

If I weigh something three times and get the same weight every time, the measurements are precise. However, that does not mean that the value that came from the weighing is actually the weight (the balance might be off), so the accuracy could be low. (not accurate to measure 6 g every time for a thing that weights 15 g, for example).

Difference between hitting the bullseye with an arrow (accurate) or placing the arrows in the same place again and again (precise). In an ideal world, we want to be sort of like Robin Hood, and be able to hit the bullseye (be accurate) and then split our earlier arrow with the next shot (be precise; do it again and again).

- DavidLv 73 weeks ago
The first thing she needs to know is the vocabulary. Then she must understand the practical applications thereof. Asking somebody else to do the work for her is a disservice.

The Master of Perception: http://tiolibooks.com/cgi-bin/blog

- Dr WLv 74 weeks ago
this is the table you posted

.. .. ... ... .. . True.. ... .. .. .. ..experimental.. . . experimental... . .experimental

.. .. .. . . . ... Value.. . . . .. ... ... value #1.. .. . .... . value #2.. .. ... .. . value #3

.. A.. .. .. .. .. 1.00... ... ... ... ... . 0.70.... ... .. ... .. .. 0.90.. ... .... ... ... . 0.80

.. B.. ... ... . .. 2.00.. ... ... ... . ... 2.50.. .. .... ... ... .. 2.48... ... ... ... ... .. 2.49

.. C.. .. ... .. .. 100.. .. ... ... .. .. ..105.. ... ... .. .. .. .. 115.. ... .... ... ... .. .110

.. D.. ... ... . .40.00 .. ... .. ... .. .. 39.00 ... .... ... . .. 38.00 ... ... ... .. ..... 37.00

.. E.. ... ... ... 40.00.. ... .... .. .. .. 35.00.. ... ... ... ... 35.00.. ... ... .. .. .. ..35.00

and you want to know

.. (5) which set of experimental data is the LEAST ACCURATE

.. (6) which set of experimental date is the LEAST PRECISE

***********

OK.. so.. let's start with an understand of what accurate and precise mean

.. (a).. experimental data is accurate if it agrees with the true value

.. (b).. a data set is more precise than another data set if the spread of the measurements

.. .. . ..is lower.. (the values are closer together)

now let's go into how we can detect ACCURACY and compare them between difference sets. Wr e can

.. (1) determine the mean and absolute range from our measurements. IF the true value

.. .. . .lies within that range, our results are accurate.. This is a quick and dirty check. (2) is better

.. (2) we can determine the mean and standard deviation from the data set. then generate

.. .. . a range from mean +/- 1 standard deviation. If the true value lies in that range, we can be

.. .. . somewhat confident our experimental values are accurate. later in stats courses, you

.. .. ..determine what that confidence in your data is but for now, let's assume if true is

.. .. ..within range of mean +/- 1 standard deviation, then experiment is accurate

.. (3) we can calculate the % error in our experiment (again, later on, you'll determine

.. .. . .confidence in that result but for now, let's assume 100% confidence) by this formula

.. .. .. .% error = | experimental mean - true value| / | true value | * 100%

... .. . .the | | are absolute error bars. the higher the % error, the less accurate the experiment

and we can compare precision of the data sets by

.. (1) comparing the absolute ranges.. the larger the range the less precise

.. (2) comparing the ranges generated from mean +/- 1 standard deviation

.. .. . the larger the range, the lower the precision

.. (3) the best way is to compare the ratios of the standard deviation / mean

.. .. ..this is called "relative precision" or "coefficient of variation".. this is best

.. .. . because the standard deviation depends on mean. example

.. .. . let's say our measurement is 119, 205,101 +/- 10,000 vs 9 +/- 1

... . .the absolute standard deviations are 10,000 vs 1 but the relative precision is

.. .. . (10,000 / 119,205,101 vs 1/9).. the 1/9 is lower precision!

anyway..let's take a look at the data. See the attached image

the calculated columns are

.. mean = sum of all measured values / 3

.. standard deviation = √ ( Σ(Xi - Xmean)² / 2)

.. experimental range #1 = mean-standard deviation to mean+standard deviation

.. experimental range #2 = lowest value to highest value

.. accurate yes / no.... accurate if true value lies withing range

.. .. .. ... .. .. .. .. .. .. . . .(in this case both ranges #1 and #2 were identical so it doesn't matter

.. ... .. .. .. .. .. ... .. .. .. . which to us. in other experiments you need to choose 1 method)

.. % error = |(mean - true value)| / | true value | * 100%

.. accuracy ranking is based on % error. The lower the % error, the better the accuracy

.. ... .. .. ... .. .. .. .. .. . . my ranking is 1-5.. 1 being the most accurate, 5 the least

.. precision ranking is based on standard deviation / mean... lowest std dev / mean is most precise

.. .. .. ... .. .. ..... .. .. . .for my ranking... #1 is most precise.. 5 is least precise

************

so.. my answers to your questions (5) and (6)

.. (5) B is the least accurate because it has the highest % error

.. (6) A is the least precise because it has the highest std dev / mean ratio

see the dataset and my calcs below

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- Anonymous4 weeks ago
I can't say about others, but I can't read the numbers well enough to answer, and I had to struggle to even read the questions.

- yakusa3000Lv 44 weeks ago
Your question is chemistry, it makes NO sense, it's mixed with unknown thoughts and words.

So, in helping you, take a lemon, mix it with water and sugar, you'll get lemonade, that's chemistry.

go away