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Stephanie Glen's Blog (80)

How to Handle Missing Data

No one “perfect” method exists for filling in missing data; You can view this one picture as a starting point with some suggestions, rather than an absolute. You may want to decide beforehand if you care about statistical power or uncertainty; If you do, you'll want to…


Added by Stephanie Glen on August 12, 2020 at 6:54am — No Comments

Calculus For Data Science: What Do You Really Need to Know?

This one picture shows what areas of calculus and linear algebra are most useful for data scientists.

If you read any article worth its salt on the topic Math Needed for Data Science, you'll see calculus mentioned. Calculus (and it's closely related counterpart, linear algebra) has some very narrow (but very useful) applications to data science. If you have a decent algebra background (which I'm assuming you do, if you're a data scientist!) then you can learn…


Added by Stephanie Glen on July 31, 2020 at 9:09am — 2 Comments

P Value vs Critical Value

P-values and critical values are so similar that they are often confused. They both do the same thing: enable you to support or reject the null hypothesis in a test. But they differ in how you get to make that decision. In other words, they are two different approaches to the same result. This picture sums up the p value vs critical value approaches.…


Added by Stephanie Glen on July 26, 2020 at 7:42am — No Comments

ANOVA vs Regression in One Picture

If you scour the internet for "ANOVA vs Regression", you might be confused by the results. Are they the same? Or aren't they? The answer is that they can be the same procedure, if you set them up to be that way. But there are differences between the two methods. This one picture sums up those differences.



Added by Stephanie Glen on July 15, 2020 at 12:13pm — No Comments

How to Communicate Data

The following graphic is based on Sam Priddy's excellent DSC/Tableau Webinar How to Accelerate and Scale Your Data Science Workflows. Sam covered many interesting points for organizing, analyzing and presenting data--including which graph is best suited for different data types. This graphic is an overview of some of Sam's points. For more…


Added by Stephanie Glen on July 8, 2020 at 9:02am — No Comments

Math vs. Statistics in One Picture

Math and statistics are vital components of any data scientist's tool box. While some view statistics as a type of math, the reality is that they are completely different subjects. Math is all about numbers and concrete answers, while statistics is making sense of numbers via educated "guesses." This one picture, based on Rossman et al's essay Some Key…


Added by Stephanie Glen on June 29, 2020 at 2:30pm — No Comments

Misleading Graphs Part 2: Ladders, Spaghetti, and Other Ways to Ruin a Graph

If you've spent any time with modeling data, you'll know that there are many pitfalls to be had when it comes to data presentation (I addressed some common pitfalls in Misleading Graphs Part 1). Misleading graphs can be the result of incorrect data collection, ignorance of the basic "rules" of data presentation (like labeling axes), or even deliberate attempts to mislead. A fourth…


Added by Stephanie Glen on June 18, 2020 at 6:00am — No Comments

You're a Data Artist, not a Data Scientist

"Data Scientist" is 2020's equivalent of the rocket scientist of the 1950's: mysterious, sexy, and well-paid. But are you actually a "scientist"? While “data science” isn't fully defined yet as an academic subject (National Academies of Sciences, Engineering, and Medicine, 2018), more and more evidence seems to point to it being more of an art, rather than a science. …


Added by Stephanie Glen on June 11, 2020 at 7:00am — 2 Comments

Misleading Graphs Part 1: Avoid These Common Mistakes

Misleading graphs are abound on the internet. Sometimes they are deliberately misleading, other times the people creating the graphs don't fully understand the data they are presenting. "Classic" cases of misleading graphs include leaving out data, not labeling data properly, or skipping numbers on the vertical axis.

I came across the following misleading graphic in a…


Added by Stephanie Glen on May 31, 2020 at 8:00am — 1 Comment

Statistics Used in Data Science (A Dictionary in One Picture)

Naming conventions are often quite different in statistics and data science, which causes quite a bit of confusion. Part of the problem with naming conventions is  that " science is the child of statistics and computer science” (Blei & Symth, 2017) . In essence, data science then is the child of two parents who speak different languages. In one sense, this makes the job of the data scientist not only to apply the knowledge from both…


Added by Stephanie Glen on May 24, 2020 at 12:08pm — No Comments

Difference Between Classification and Regression in One Picture

Regression and classification are both supervised machine learning techniques that use known data to make predictions. Where they differ is in what type of question you want answer, and how your output data is structured.  For example, do you want discrete, categorical answer choices, like yes/no, or a range of possible values from 0 to 100? This one picture shows the basic differences between the two methods.…


Added by Stephanie Glen on May 17, 2020 at 5:58am — No Comments

Inference vs Prediction in One Picture

Inference and prediction are two often confused terms, perhaps in part because they are not mutually exclusive. Both provide pieces of the "What is data telling me?" puzzle. In fact, many inferential questions are raised as a result of predictions: For example, you might predict how input variables X, Y, and Z affect an output variable B. Then you can…


Added by Stephanie Glen on May 10, 2020 at 6:12am — 1 Comment

Difference between Binomial, Poisson and Hypergeometric Distribution in One Picture

There are a few key differences between the Binomial, Poisson and Hypergeometric Distributions. These distributions are used in data science anywhere there are dichotomous variables (like yes/no, pass/fail). This one picture sums up the major differences.…


Added by Stephanie Glen on April 30, 2020 at 9:45am — No Comments

Data Mining vs Statistics in One Picture

Data mining includes statistics and elements of statistical analysis.  Some people describe the two as interconnected, others as them being on a continuum. This one picture shows an overview of how statistics and…


Added by Stephanie Glen on April 26, 2020 at 11:04am — 1 Comment

How to Get Your First Data Science Job: Go Dog Sledding

If you plug "statistics interview questions" into a search engine, you're going to get hundreds of questions and answers. And if your interview is looming in a few days, trudging through (and trying to memorize) hundreds of questions probably isn't your idea of a fun weekend. And if you're looking for that shoe in, having the perfect answer to every question might not be your best plan of attack. Why? Because that's what everyone else is doing.

So how do you stand out…


Added by Stephanie Glen on April 18, 2020 at 5:10am — 2 Comments

Steps of Hypothesis Testing in One Picture

Hypothesis testing can be an overwhelming topic to grasp if you're new to the subject. As well as dealing with all of the different terminology, you have to perform several steps to run a test. Even if you use software, you have decisions to make at each step, such as what you're testing in the first place and what kind of wiggle room for error you're…


Added by Stephanie Glen on April 6, 2020 at 12:58pm — No Comments

Choosing the Correct Statistical Test

In a previous blog post, I created a flow chart showing how to choose a statistical test from a dozen different tests. While researching the article, I came across a short and sweet version which only includes four of the more basic tests:…


Added by Stephanie Glen on March 30, 2020 at 6:30am — 1 Comment

Lognormal, Weibull, and Gamma distribution in One Picture

At first glance, the Lognormal, Weibull, and Gamma distributions distributions look quite similar to each other. Selecting between the three models is "quite difficult" (Siswadi & Quesenberry) and the problem of testing which distribution is the best fit for data has been studied by a multitude of researchers.

If all the models fit the data fairly…


Added by Stephanie Glen on March 27, 2020 at 7:30am — No Comments

Statistical Uncertainty: Why are Covid-19 Figures so Varied?

If you've been keeping up on the statistics for Covid-19 in the last week (and who hasn't?), you've probably noticed a wide variety of projections for deaths in the United States, ranging from the "best-case" scenario  (327 people) to the "doomsday" figure (2.2 million). Recent statistics published include:

  • 327 to 1.6 million (Former Former CDC director Tom Frieden, cited in the…

Added by Stephanie Glen on March 21, 2020 at 8:00am — 1 Comment

Understanding Covid-19 Statistics (in plain English)

My original intent with this article was to write about how to understand statistics in general. However, with the global pandemic on everyone's minds right now, it seems blithe to write an article on understanding statistics without a nod to current events. If you're uncomfortable or unfamiliar with statistics, you might find the facts and figures surrounding Covid-19 hard to decipher. Let's break down the key statistics into plain English and shed a little light on a few…


Added by Stephanie Glen on March 17, 2020 at 6:30am — 5 Comments


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