What is a Sampling Distribution?

The sampling distribution is one of the most important concepts in inferential statistics, and often times the most glossed over concept in elementary statistics for social science courses. This article will introduce the basic ideas of a sampling distribution of the sample mean, as well as a few common ways we use the sampling distribution in statistics. When we conduct a study in psychology, this almost always includes taking a sample and measuring some aspect…

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Signal Detection: Decision Making in Uncertainty

We all experience uncertainty: How did I do on that test? What do they think of me? Where did I leave my keys? Is my phone ringing? In these and other uncertain situations,

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An Illustrative Guide to Statistical Power, Alpha, Beta, and Critical Values

From my interactions with undergraduate students, it seems that even though these definitions are easy to recite, they are difficult to be integrated into a comprehensive whole. I hope here to show how to conceptually integrate them into a cohesive picture. Everything begins with reality: the “Reality Continuum” I call this green line “Reality Continuum” (rather grand, no?) because you will take your ideas, and do a reality check against it via data analysis (within the traditional statistical framework–it is definitely NOT…

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Mediating and Moderating Variables Explained

What is the difference between a mediator and a moderator? One of my former academic advisors used to always say “be a walking laboratory”. I think it’s a very poetic way of describing a core feature of psychological research—to come up with theories or explanations for various phenomena we observe. Sometimes there isn’t a clear-cut relation between a dependent and independent variable. In those cases, a mediating variable or a moderating variable can provide a…

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The Significance of Impression Formation: Reinterpreting Early Social Psychology Findings Using Modern Stats

Solomon Asch may be best known in social psychology for his 1951 Conformity Studies in which he brought participants into a room with seven confederates—actors pretending to be other participants—and had them recount the length of a line.  Before demonstrating that normative pressure can lead people to lie, Asch was one of the foremost researchers on impression formation.  He was interested in how we judge others and their personality based off small bits of information. 

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Python for the Social Sciences: Toolkit Essentials

  Why Py? Why should psychologists, or social scientists more generally, care about programming? The fact is anyone who uses softwares for data analysis relies on programming and many wonderful tools exist to give researchers improved control over their data for more efficient workflow. Although learning programming may seem an insurmountable task, with the right tools a few simple lines of code can accomplish wonderful things. I hope this blog will present, in a very…

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Odds Are: On the difference between odds, probability, and risk ratio.

Odds, Probability, Chance, Risks: Interchangeable? Not so much. What does it mean to say “smokers are X times more likely to get lung cancer than non-smokers?” What about when the weather channel says, “there is a 10% chance of rain?” The odds of 1 to 10 of winning? These words are often used in casual conversations as somewhat interchangeable, and can be rather confusing. I remember being very excited to learn about them for the first…

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How will Big Data shape psychology research?

I’m sure all of you have heard of the Big Data movement going on right now. From the Harvard Business Review to David Brooks in the NY Times, everyone seems to be talking about the power of big data to provide “insights” into the inner workings of the world. Of course as a scientist, recognizing the power of data is not news to me. But I was interested in an article in the Psychological Science Observer that talks about how…

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Biased results — field of psych takes the heat

The pressure to publish positive findings (instead of null results) is present across scientific discipline, but several researchers have argued that the field of Psychology is the most biased offender.  An article posted last week in Nature.com discussed these biases – and presents two potential solutions one of which was suggested by UCLA researcher Dr. Matt Lieberman.  Click here to read the full article and suggested solutions.

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Revisit: fMRI and the “lit up” brain

I wrote a post a few months ago about some common misconceptions about functional magnetic resonance imaging (fMRI), and one of my main points was that the term  ‘lights up”, which is often used when describing the areas of the brain that respond to a task, is misleading. Here is what I said on the subject: First, fMRI does not detect electrical changes in the brain, as ‘lights up’ would imply.  Neurons in the brain communicate…

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“…the difference between significant and not significant is not itself necessarily significant.”

The quote above comes from a perspective published in Nature Neuroscience this past summer by Nieuwenhuis and colleagues. They detail a surprisingly common mistake in the statistical analyses carried out by some studies published in prominent journals. It might be easier to first illustrate the mistake with an example. Let’s say I give a control group and a treatment group a task. To measure performance, I record how quickly each subject completes it. The control…

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What Can Effect Sizes Do for You? A Quick Tutorial for a Deeper Understanding of Psychological Research

I listen to a lot of podcasts in which various psychological articles are often discussed (e.g., stuff you should know, radiolab, etc.).  As a psychologist, I am often frustrated when a podcast mentions a study’s finding (e.g., having a sister is associated with better self-esteem than having a brother) but then says something like this: “well, I’m kind of suspicious of that finding/we should take that finding with a grain of salt/I kind of question…

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Correlation, causation, or association – What does it all mean???

From allaboutaddiction.com: A comment posted by a reader on a recent post reprimanded me for suggesting that marijuana caused relationships to go bad. While in that instance the reader was mistaken, as I had specifically used the word associated, the comment made me think that maybe I should explain the differences here. I’m a scientist studying addiction, and in the field, it’s very important to be clear about what each of the words you use…

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