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Angst Over ANOVA Assumptions? Ask the Assistant.

Do you suffer from PAAA (Post-Analysis Assumption Angst)? You’re not alone.

Checking the required assumptions for a statistical  analysis is critical. But if you don’t have a Ph.D. in statistics, it can feel more complicated and confusing than the primary analysis itself.

How does the cuckoo egg data, a common sample data set often used to teach analysis of variance, satisfy the following formal assumptions for a classical one-way ANOVA (F-test)?

  • Normality
  • Homoscedasticity
  • Independence

Are My Data (Kinda Sorta) Normal?

To check the normality of each group of data, a common strategy is to display...

Using Probability Plots to Understand Laser Games Scores

There is more than just the p value in a probability plot—the overall graphical pattern also provides a great deal of useful information. Probability plots are a powerful tool to better understand your data.

In this post, I intend to present the main principles of probability plots and focus on their visual interpretation using some real data.

In probability plots, the data density distribution is transformed into a linear plot. To do this, the cumulative density function (the so-called CDF, cumulating all probabilities below a given threshold) is used (see the graph below). For a normal...

Using nonparametric analysis to visually manage durations in service processes

My main objective is to encourage greater use of statistical techniques in the service sector and present new ways to implement them.

In a previous blog, I presented an approach you can use  to identify process steps that may be improved in the service sector (quartile analysis). In this post I'll show how nonparametric distribution analysis may be implemented in the service sector to analyze durations until a task is completed.

Knowing how much time you need to complete a task may be very useful when assessing process efficiency, and is an important factor in many businesses.

Consider a...

Using Hypothesis Tests to Bust Myths about the Battle of the Sexes

In my home, we’re huge fans of Mythbusters, the show on Discovery Channel. This fun show mixes science and experiments to prove or disprove various myths, urban legends, and popular beliefs. It’s a great show because it brings the scientific method to life. I’ve written about Mythbusters before to show how, without proper statistical analysis, it’s difficult to know when a result is statistically significant. How much data do you need to collect and how large does the difference need to be?

For this blog, let's look at a more recent Mythbusters episode, “Battle of the Sexes – Round Two.” I...

Truth, Beauty, Nonparametrics & Symmetry Plots

  “Shall I compare thee to a standard normal distribution?
  Thou art more symmetric and more bell-shaped…”  — Melvin Shakespeare (William’s lesser-known statistician brother)

The Greek philosopher Aristotle believed that symmetry was one of the primary elements of the universal ideal of beauty. Over 2000 years later, emerging research seems to bear him out. 

Studies suggest we tend to be more attracted to people with symmetrical bodies. Using motion-capture technology to record the movements of people dancing to a popular song, one recent study concluded that we even prefer those who dance...

The Non-parametric Economy: What Does Average Actually Mean?

Watching the news in the U.K. is like listening to the same old annoying record over and over again: "Uncertainties about the European economy...disappointing employment figures...stubbornly  high inflation...increasing pressures on  the average U.K.  household  to make ends meet…"

How about some good news, please?

Actually, there is some good news…that is, if you are a top executive for one of the FTSE 100 companies. According to the pay research company Incomes Data Services (IDS), the median remuneration for the directors of the U.K.'s top businesses rose 50% over the past year, which took...

Quality Analysis and Outliers: This Time Samoa has Really Crossed the Line

I am an outlier. Of the people who work in my department, I go to the fewest meetings, I talk with others the least, and I make the least use of our exercise facilities. But this is not because I am negligent, anti-social, or lazy. It is because I am separated from the rest of my department by about 10,000 miles.

You see, my family and I have had the opportunity recently to move to beautiful Sydney, Australia. And at 3 PM on Friday in Pennsylvania, while my colleagues are discussing nonparametric statistics, SIPOC, and project charters, I'm plotting my route to the beach because it is 7 AM...

Get a Head Start: Understand Your Data--Before You Analyze It

We humans do have a tendency to succumb to gold rush fever.

And this can happen even in the left-brained, rational field of statistics.

After we collect our data, it’s difficult to resist the urge to desperately dash for p-values, as if they were 70% off at Macy’s the day after Thanksgiving.

But no matter how well-versed you are in statistics, it’s good practice to get into the habit of intuitively “knowing” your data well before you dive into a sea of complex calculations. It helps ensure you’ll fully understand your analysis results, avoid careless errors, and draw sound conclusions.

Minitab’s...