Accuracy & precision

background [prelab assignment (18 points) due at the begining of lab]

1. what's the difference between accuracy versus precision ?

2. what's the use of the below statistics tests ?

a. t-test versus 1-anova

b. F-test involving the variance

c. importance of test to check if experimental data is described by a normal distribution

3. relate the below items.

a. variance & standard deviation

b. standard deviation, accuracy, & precision.

purpose

use of various devices to measure the volume of a liquid

compare the accuracy & precision of various equipment to measure the volume of a liquid

is the data described by the normal distribution ?

materials

electronic balance, weigh boat

10 mL pipet, modified 10 mL pipet, 10 mL graduated cylinder, 50 mL beaker, water

100 mL graduated cylinder, 100 mL volumetric flask - for 100 mL

methods / data analysis

methods: each group generates their own independent data, which is to be shared with the classs. maximum of 3 students / group.

measure 8.2 (or 100) mL of water in the various devices then transfer the water to a weigh boat on the electronic balance

measure / record the mass of water as a function of the measuring device. the person using the device should be unaware of the mass measurements to minimize any feedback; thereby, maintaining independent measurements

each student in the group obtains a data for each device,

if data is not described by the normal distribution, then each group, calculate the mean of your duplicate measurments - recall, prior lab about the central limit theorem

data analysis

student design

content of lab report [45 points; reminder: a pair of students may submit a lab report]

data analysis; include appropriate statistics test and support your answer to the below prompts by referring to your statistics test results as appropriate

histogram of your measurements

is the data described by a normal distribution ? based on ___

qualitatively, examine the histogram

use a statistics test

is there a need to evoke the Central Limit Theorem ? justify.

if there is a clear need to evoke the Central Limit Theorem, then adjust your analysis accordingly and clearly point it out and show that the adjustment is valid. if the adjustment is clearly invalid / insufficient, then act accordingly, i.e. do not do any subsequent statistics tests and state this reason.

what is the relative precision among the various equipment ?

what is the relative accuracy among the various equipment ?

discussion

is there a relationship between the relative accuracy versus relative precision in the various equipment. refer to data (and / or statistics) to support your response.

in theory, there should be a difference in the relative precision in your data among the various equipment; rationalize. (hint: assume the mesurement devices are cylinders and refer to the formula for the volume of a cylinder; do not use calculus to solve the problem)

Resources

mathematica - statistics files

Excel - histogram: (see section on formula & link to drawing histograms - step 3. fixing output)