Pre-Lab: Data Analysis

What does accuracy determine?

How close a value is to the true value

What is precision?

How close a value is to the rest of the data set

When is data considered to have good precision?

When the standard deviation is less than 5%

What is the equation for standard deviation (xi is the data values and n is the number of data points)?

sqrt(sum(xi-average)²/(n-1))

How is error different from a mistake?

Error occurs even when a measurement/experiment was performed correctly

What is systemic error?

Error inherent to the measuring device and its use

What are common causes of systemic error?

Not calibrating the measuring device properly, using the wrong device for the measurement, or using the proper measuring device improperly

What causes random error?

It comes from multiple measurements from the same measuring device

What is the best way to test for random error?

Perform a Q test on each data point in a set and remove outliers to improve precision

How can a scientist determine if multiple data sets can be combined?

Use the t-test

What is the formula for finding the standard deviation of pooled data sets (𝑠1 is the standard deviation of the first data set, 𝑛1 is the number of data points in the first set, 𝑠2 is the standard deviation of the second data set, and 𝑛2 is the number of data points in the second set)?

sqrt((s1²(n1-1)+s2²(n2-1))/(n1+n2-2))

What is the formula to calculate t_calc(where s-pooled is the standard deviation of the pooled data sets and n1 and n2 are the number of data points in the sets)

abs(average1-average2)/(s-pooled)*sqrt(n1*n2/(n1+n2))

When can two sets be combined?

If t-calc is less than the t that corresponds to the number of data points in the set

In general, what is the most accurate and precise glassware for measuring liquids?

Volumetric pipettes and flasks

What will we typically use to measure the volume of liquids in this class?

A graduated cylinder

Where do you measure the volume of a liquid?

At the meniscus (at the bottom of the curve)