Browsing All Posts published on »May, 2012«

The Key to the Birthday Problem: uniqueValues( )

May 30, 2012

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It’s a famous probability problem: given N people in a room, what’s the probability that at least two of them share a birthday? It’s famous because the answer is often surprising: a remarkably small number (23) will give you a probability over 50%. How do you simulate it in Fathom? The key is going to be […]

Starting with Counts and Making the Collection

May 27, 2012

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In an earlier post, we talked about how to do statistical tests and estimates using summary statistics. But sometimes you start with a one- or two-way table of counts, and you want the actual collection of data. Here’s one way to get it. It’s a workaround, but it’s reasonably quick: Figure out how many different […]

Random Walk

May 26, 2012

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The random walk is a thought experiment (we hope) that underpins a lot of formal statistics and error analysis. The idea is that for every step, you flip a coin. Heads, you move forwards; tails, you move back. You take a total of n steps. How far are you likely to travel? If you’re experienced […]

Exponential Decay Simulation

May 9, 2012

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This comes from a Fathom listserv query by David Petro: 1. Flip 1000 coins 2. Remove the heads and count up the tails 3. Flip the remaining tails again 4. Repeat 2 & 3 until no coins remain 5. Graph the number of tails after each experiment. This is what I have tried I Have […]

How to Do a t-Test in Fathom

May 3, 2012

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How do you do a regular old t-test, no randomization? It’s easy, but different from how you do it in other programs. 1. Make a “test” object. Look at the shelf (a.k.a. toolbar), find the “test”, and drag one into your document. 2. Choose the kind of test you want from the menu. Here, we’re […]

Make Your Own Binomial Machine

May 2, 2012

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Here’s how to make a Fathom simulation that will let you change the parameters of a binomial distribution quickly. Note that this may not be best for instruction. In a new document, make two new sliders, N and p. Make a table and give it 1000 cases. Make one attribute (call it successes or anything you […]

What If You Just Have Summary Statistics?

May 2, 2012

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This came from an AP-Stat listserv discussion April 2012: Hello Tim, Corey, Dennis – I also use Fathom and appreciate its power and flexibility in the educational setting. However, a serious limitation for me is Fathom’s inability of handling categorical data from summarized values as those from data tables in many AP textbook exercises. Question: […]