α 
Producer's risk 
β 
Consumer's risk (Also see the row below) 
β 
Shape parameter for Weibull distribution 
χ^{2} 
Value of chisquare distribution 
C_{p} 
Capability index 
C_{pk} 
Capability index considering process centering 

Average difference between two samples 
η 
Median 
H_{o} 
Null hypothesis 
H_{1} 
Alternate hypothesis 
k 
Letter used for number of bins, or number of factors 
κ 
Cohen's kappa 
μ 
Population mean 
n 
Number of data points or sample size 
N 
No of total observations 
p 
Probability of an event 
P_{p} 
Process performance index 
P_{pk} 
Process performance index considering process centering 
q 
(1p) i.e., Probability that the event does not occur 
r 
Correlation coefficient 

Sample standard deviation 
σ 
Population standard deviation 
S_{e} 
Standard deviation of errors 
σ_{p} 
Standard deviation of process output 
σ_{t} 
Standard deviation of observed variation 
σ_{m} 
Standard deviation of measurement system 
S_{p} 
Pooled standard deviation 
σ^{2} 
Variance 
S_{x} 
Sample standard deviation of x 

Standard deviation of sample means 
S_{xy} 
Sample covariance 
S_{y} 
Sample standard deviation of y 
θ 
Scale parameter for Weibull distribution 
X 
Key process input variable 
x or x_{i} 
Individual values of data 

Sample mean 

Grand mean 
Y 
Key process output variable 
Z 
Value of standard normal transformation 