Statistical Sampling and Six-Sigma

In quality management, statistical sampling and standard deviation are two key concepts.

In statistical sampling, sample size usually is determined by

Sample size = 0.25 x (certainty factor/acceptable error).

Desired certainty	Certainty factor
95%	1.960
90%	1.645
80%	1.281

6σ - In a normal distribution, 68.3% of the population is within 1σ. 95.45% within 2σ. 99.73% within 3σ. 99.9937% within 4σ. 99.999943% within 5σ. 99.9999998% within 6σ.