Precision and Accuracy of Measurement

An AP Biology Case Study

Validation Before equipment is used in a laboratory

setting, its validity must be determined.

As an AP biology student it is important to: Recognize how statistics may be used as a

part of the validation process. Learn to use various tools to measure volume. Learn to upload data in google docs and

analyze large data sets in Excel.

Salinity of Water The salinity of water is one factor in the determination

of which organisms can grow.

You are working as the manager of a sewage treatment plant. The bacteria necessary to break down raw sewage do not grow in high salinity.

Recent high rains have caused seawater to infiltrate your systems.

You have tried to mitigate the situation and want to determine if you now have pure H2O flowing through your system’s in-flow pipes.

Before you test your water…you must validate your equipment using pure water.

Techniques Accuracy:

You have a balance that measures to the thousands of a gram.

You have various tools to measure volume in mL

You know the density of pure water is 1 g/mL.

What measure can you use to determine the accuracy of each measurement tool?

Techniques Precision

You have the following tools to use to measure volume.

Since you are testing for the first time, you want to figure out which tool is most precise so you can choose the appropriate tool later.

What measurement can you use to evaluate the precision of each measurement tool?

Tools 10 mL graduated cylinder (measures to 0.2 ml)

1 ml plastic pipette (measures to 0.25 ml)

1 ml graduated pipette (measures to 0.1 ml)

1 ml micropipette (measures to 0.001 ml; but not suggested for measuring amounts below 200 ul)

Which tool do you think will produce the most accurate results?

Which tool do you think will produce the most precise results?

Conclusions

Which tool was most accurate? Explain your conclusion based on the data.

Which tool was most precision? Explain your conclusion based on the data

Which tool would you use to validate your water sample and why?

Why is validating equipment an important part of the experimental process?

What sources of error may have resulted in your validation process?