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MCHART Statement 
process mean (expected value of the population of measurements)  
process standard deviation (standard deviation of the population of measurements)  
mean of measurements in i^{ th} subgroup  
n_{i}  sample size of i^{ th} subgroup 
N  the number of subgroups 
x_{ij}  j^{ th} measurement in the i^{ th} subgroup, j = 1,2,3, ... , n_{i} 
x_{i(j)}  j^{ th} largest measurement in
the i^{ th} subgroup. Then

weighted average of subgroup means  
M_{i}  median of the measurements in the i^{ th} subgroup:

average of the subgroup medians:
 
median of the subgroup medians. Denote the
j^{ th} largest median by
M_{(j)} so that . Then
 
e_{M}(n)  standard error of the median of n independent, normally distributed variables with unit standard deviation (the value of e_{M}(n) can be calculated with the STDMED function in a DATA step) 
Q_{p}(n)  100p^{ th} percentile (0<p<1) of the distribution of the median of n independent observations from a normal population with unit standard deviation 
z_{p}  100p^{ th} percentile of the standard normal distribution 
D_{p}(n)  100p^{ th} percentile of the distibution of the range of n independent observations from a normal population with unit standard deviation 
The following table provides the formulas for the limits:
Table 35.22: Limits for Median ChartsControl Limits 
LCLM = lower limit 
UCLM = upper limit 
Probability Limits 
LCLM = lower limit 
UCLM = upper limit 
Note that the limits vary with n_{i}. In Table 35.22, replace with if you specify MEDCENTRAL=AVGMEAN, and replace with if you specify MEDCENTRAL=MEDMED. Replace with if you specify with the MU0= option, and replace with if you specify with the SIGMA0= option. The formulas assume that the data are normally distributed.
You can specify parameters for the limits as follows:
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