Statistics

Question 1

Define accuracy

Answer 1

How close a number is to what it should be, by comparing a number to known/accepted value

Question 2

Define precision

Answer 2

Number of decimal places of a measured number (reproducibility)

Question 3

Describe accuracy and precision (bull’s eyes)

Answer 3

Good accuracy - Closer to the bull’s eye

Good precision - Closer each point is to eachother

Question 4

Calculating absolute error

Answer 4

Difference between measured and true value

Question 5

Calculating relative error

Answer 5

Absolute error divided by true value

Question 6

What method is used to measure precision?

Answer 6

Standard deviation

Question 7

What is s^2?

Answer 7

Variance/RSD (%)

Question 8

What is Gaussian rounding?

Answer 8

Avoiding biased results by rounding to the nearest even number

Question 9

What is standard deviation?

Answer 9

Measure of variation

Question 10

What are the 3 types of errors?

Answer 10

Gross, Systematic, Random

Question 11

Describe gross errors

Answer 11

Occurs sometimes, large and cause results to be high/low (lead to outliers)

Question 12

Describe systematic errors

Answer 12

Definite values, lead to bias, affects all data

Question 13

Describe random errors

Answer 13

Uncontrollable variables, undetectable uncertainties

Question 14

What is associated with systematic error?

Answer 14

Poor accuracy

Question 15

What is associated with large random error?

Answer 15

Poor precision

Question 16

What is random error a representation of?

Answer 16

The distribution around the mean (outer areas of mean in distribution curve)

Question 17

Describe Dixon’s Q-test

Answer 17

Used for gross errors by comparing difference between samples and nearest measurement

Question 18

What is the formula for the Q-test?

Answer 18

(Suspect value - Nearest value) / (Largest value - Smallest value)

Question 19

Define confidence interval (CI)

Answer 19

The probability that interval estimate includes the population mean (u)

Question 20

What is the equation for confidence interval for the mean?

Answer 20

u = x +/- t (s/ 2/n)
u = Population mean
x = Sample mean
s = Standard deviation
t = Student's t-value
n = Number of measurement

Question 21

What is SEM?

Answer 21

Standard error of the mean - (s/ 2/n)

Question 22

What is the best confidence percentage to use?

Answer 22

95% unless told

Question 23

How to calculate t-value?

Answer 23

Find degree of freedom by number of samples - 1