Too Much Data, Too Little, or Just Enough? Ask Minitab's Power and Sample Size Tools

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Minitab Statistical Software’s Power and Sample Size tools can tell users how much data they need to be sure about their results.

Minitab’s Power and Sample Size tools help users balance the need for statistical power with the expense of gathering data.

Minitab 16 Statistical Software’s Power and Sample Size tools can tell users how much data they need to be sure about their results.

Gathering data for statistical analysis is like tasting fine wine—it's important to get just the right amount.

Gathering data for statistical analysis is like tasting fine wine—it's important to get just the right amount. With wine, too small a sip prevents the accurate assessment of a subtle bouquet, but too large a sip overwhelms the palate. Similarly, gathering too little data limits the reliability of an analysis, but gathering too much data wastes resources.

An excessively large or small sip of wine isn't the end of the world, but the stakes are higher people who need to analyze data. Fortunately, Minitab 16 Statistical Software’s Power and Sample Size tools can determine exactly how much data is needed to be sure about the results of an analysis.

Minitab’s Power and Sample Size tools help users make sure they collect enough data to conduct a reliable analysis, while avoiding wasting resources by collecting more data than they need. Minitab can also asses the statistical power of tests that have already been run and estimate the sample size needed to obtain a specific margin of error.

Statistical power is the likelihood that a test will identify a significant difference or effect when one truly exists. Testing critical airplane parts, for example, demands a higher degree of certainty than testing DVD players.

Minitab helps balance the need for statistical power with the expense of gathering data by answering this question: How much data do you need? This deceptively simple question takes many forms:

-- How many samples are needed to determine if the average thickness of paper differs from one supplier to another?

-- How many voters should be sampled to be 95% confident that the proportion supporting a candidate is within 3% of its true value?

-- How many times should an experiment be replicated to have at least an 85% chance of detecting the factors that significantly affect a manufacturing process?

In most cases, people want to collect just enough data to ensure they have sufficient power to draw sound conclusions. Minitab Statistical Software includes tools to estimate sample size and power for the following statistical tests:

-- Sample Size for Estimation
-- 1-Sample Z
-- 1- and 2-Sample t
-- Paired t
-- 1 and 2 Proportions
-- 1- and 2-Sample Poisson Rate
-- 1 and 2 Variances
-- One-Way ANOVA
-- 2-Level Factorial Design
-- Plackett-Burman Design
-- General Full Factorial Design

Minitab's power and sample size capabilities also allow users to examine how different test properties affect each other. For example, a user who needs to perform a two-sample t-test can calculate:

-- Sample sizes—the number of observations in each sample.

-- Differences (effects)—the minimum difference between the mean for
one population and the mean for the other that the test can detect.

-- Power—the probability of detecting a significant difference when one truly exists.

If a user enters values for any two of these properties, Minitab will calculate the third. For instance, values for the minimum difference and power are entered, Minitab determines the sample size required to detect the specified difference at the specified level of power.

The Power and Sample Size tools in Minitab 16 make it easier than ever for users to be sure they can count on the results of their analyses. A free, fully-functional 30-day trial of Minitab 16 Statistical Software is available at http://www.minitab.com/products/minitab/free-trial.aspx

About Minitab Inc.

Minitab Inc. is one of the world's leading developers of statistical analysis and process improvement software for academic and commercial users.

Minitab Statistical Software is the preferred data analysis tool for businesses of all sizes and is used in more than 80 countries by thousands of distinguished companies, including Toshiba, DuPont, Boeing, Royal Bank of Scotland, Nestlé and the leading Six Sigma consultants. It has been used to implement virtually every major Six Sigma quality improvement initiative, and to teach statistics in over 4,000 colleges and universities worldwide.

Quality Companion by Minitab is the package professionals use to plan and execute Six Sigma projects in companies around the world, including Xerox, ITT Industries, Providence Health System, Nissan North America, and LexisNexis.

Quality Trainer by Minitab provides easy access to quality statistics expertise whenever you need it. This subscription-based online learning course lets you learn or refresh your knowledge anytime and helps you use Minitab to apply statistics properly. Interactive lessons based on real problems make concepts easy to retain.

Minitab Inc., headquartered in State College, Pa., operates offices in the United Kingdom, France, and Australia, and has additional representatives throughout the world. For more information, visit http://www.minitab.com.

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Eston Martz
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