To determine the sample size for a confidence interval for the difference of two means to have a specified margin-of-error we need to apply the following formula:

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Knowing the proportions of some occurrence over all possible occurrences is important in countless applications. A politician would like to know what proportion of voters in his electorate will vote for him.

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The biggest enemy for quality and cost is variability. For example, in manufacturing the greater the variability, the greater the chance of producing non-conforming product.

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To determine the sample size for a confidence interval to have a specified margin-of-error we need to apply the following formula: N = Z_Value(alpha / 2) * Sigma / (margin-of-error)^2. Where alpha is the specified level of significance.

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The Cp and Cpk Index has been used for many decades in Quality Assurance as a means of summarizing process capability into a simple index.

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It can be argued that philosophically the standard deviation is more important than the mean. The standard deviation is a measure of variability and some have called variability Qualityâ€™s biggest enemy.

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The theory behind hypothesis testing for the ratio of two standard deviations is based on the theory for hypothesis testing of two variances where the variance is equal to the standard deviation ^2.

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Hypothesis testing for the proportion has one of the most diverse applications and is relevant particularly in manufacturing, health, political campaigning and market research.

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The Cp and Cpk index remain one of the most popular Quality Indexes used by manufacturing. The baseline is considered 1.0 being the borderline case.

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There are many situations where it is necessary to obtain an average reading of some variable. For example, the average calorie consumption by people from various demographic categories per day.

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There are many situations where the analyst needs to decide on the difference between two means. Several researchers have reported that the difference in two means can be more important than information on the means separately.

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