The Analysis Factor

Statistical Consulting, Resources, and Statistics Workshops for Researchers

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3 Tips to Make Interpreting Moderation Effects Easier

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Understanding moderation is one of those topics in statistics that is so much harder than it needs to be.

Here are three suggestions to make it just a little easier.

1. Realize that moderation just means an interaction

I have spoken with a number of researchers who are surprised to learn that moderation is just another term for interaction.

Perhaps it’s because moderation often appears with discussions of mediation. Or because we tend to think of interaction as being part of ANOVA, but not regression.

In any case, both an interaction and moderation mean the same thing: the effect of one predictor on a response variable is different at different values of the second predictor. [Read more…] about 3 Tips to Make Interpreting Moderation Effects Easier

Inter Rater Reliability–A Few Good Resources

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Inter Rater Reliability is one of those statistics I seem to need just seldom enough that I forget all the details and have to look it up every time.

Luckily, there are a few really great web sites by experts that explain it (and related concepts) really well, in language that is accessible to non-statisticians.

So rather than reinvent the wheel and write about it, I’m going to refer you to these really great sites:

If you know of any others, please share in the comments.  I’ll be happy to add to the list.

Teach Statistics Before Calculus? An interesting idea by Arthur Benjamin

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I don’t usually get into discussions here about the teaching of statistics, as that’s not really the point of this blog.

Even so, I found this idea fascinating, and since this blog is about learning statistics, I thought you may find it interesting as well.

The following is a TED talk by Arthur Benjamin, who is a math professor at Harvey Mudd College.  Let me start by saying he is awesome.  I already watched his Mathemagician TED talk with my kids*, so when I found this, I already expected it to be very good.

I wasn’t disappointed.

*if you too are on an active campaign to instill a love of math in your kids, I highly recommend it.

Here are two of my favorite quotes, keeping in mind that I took calculus in high school and I LOVED it.  Even so, he’s got some really good points:

“Very few people actually use calculus in a conscious, meaningful way in their day-to-day lives.  On the other hand, statistics–that’s a subject that you could, and should, use on a daily basis.”

“If it’s taught properly, it can be a lot of FUN. I mean, probability and statistics–it’s the mathematics of games and gambling, it’s…it’s analyzing trends, it’s predicting the future.”

If you find the video isn’t working, you can watch it directly on the TED site (this is the first time I’ve embedded a video). 🙂


Stratified Sampling for Oversampling Small Sub-Populations

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by Ritu Narayan

Sampling is a critical issue in any research study design. Most of us have grappled with balancing costs, time and of course, statistical power when deciding our sampling strategies.

How do we know when to go for a simple random sample or to go for stratification or for clustering? Let’s talk about stratified sampling here and one research scenario when it is useful.

One Scenario for Stratified Sampling

Suppose you are studying minority groups and their behavior, say Yiddish speakers in the U.S. and their voting.  Yiddish speakers are a small subset of the US population, just .6%. [Read more...] about Stratified Sampling for Oversampling Small Sub-Populations

Adding Statistical Equations to Word using Microsoft Equation Editor

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Have you ever tried to type a complex fraction, like a logit link, using Word, by lining up two rows of type?

Or a regression model equation?  It’s possible, but it takes forever to subscript all those i’s and change the font of all your B’s to β’s.

I used to, and it’s not easy.

What saved me, years ago, is the Microsoft Equation Editor.

I just mentioned it to a client the other day.  She was thrilled at the ease and flexibility of it, so I thought I’d better share this.

So, to insert a beautiful equation into Word, Powerpoint, or whatever [Read more…] about Adding Statistical Equations to Word using Microsoft Equation Editor

On Data Integrity and Cleaning

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This year I hired a Quickbooks consultant to bring my bookkeeping up from the stone age.  (I had been using Excel).

She had asked for some documents with detailed data, and I tried to send her something else as a shortcut.  I thought it was detailed enough. It wasn’t, so she just fudged it. The bottom line was all correct, but the data that put it together was all wrong.

I hit the roof. Internally, only—I realized it was my own fault for not giving her the info she needed.  She did a fabulous job.

But I could not leave the data fudged, even if it all added up to the right amount, and already reconciled. I had to go in and spend hours fixing it. Truthfully, I was a bit of a compulsive nut about it.

And then I had to ask myself why I was so uptight—if accountants think the details aren’t important, why do I? Statisticians are all about approximations and accountants are exact, right?

As it turns out, not so much.

But I realized I’ve had 20 years of training about the importance of data integrity. Sure, the results might be inexact, the analysis, the estimates, the conclusions. But not the data. The data must be clean.

Sparkling, if possible.

In research, it’s okay if the bottom line is an approximation.  Because we’re never really measuring the whole population.  And we can’t always measure precisely what we want to measure.  But in the long run, it all averages out.

But only if the measurements we do have are as accurate as they possibly can be.


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