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Sampling Distribution & Central Limit Theorem

sampling distribution

Understanding sampling distributions is really important, but very few researchers do! In the sample size post I introduced the idea that we look at the results of an experiment by investigating what would happen if we did the same experiment lots of times. To do that we need to use something called the ‘Sampling distribution’ – […]

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Statistical Basics – What is a Random Variable?

random_variables

This term “random variable” is a bit confusing, and not helped by the way it is usually taught! “Random variable” is really shorthand for  “the answer to this question is like rolling a dice or tossing a coin.” Let’s unpack… If I toss a normal coin there is a 50% chance it will land on […]

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Statistical Basics – Variables

categorical numeric variables

To do statistics we need data. But more than that, we need variables, things that can vary.  “What is happening with this thing that varies?” Is a pretty good summary of any statistical problem. I like to think of a variable as a question, a question with more than one possible answer. Visualise an excel spreadsheet while you think about variables – a spreadsheet […]

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Statistical basics – Mean & Median

mean median skewness

This post has been summarised into a handy cheat sheet – you’re welcome! You probably already know what the mean and median are, but there is actually a lot to learn here.  Confusion about mean and median can derail more advanced statistical topics, or worse — cause you to make crazy conclusions about your data. Let’s go. […]

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Statistical Basics – Parameter Estimation

parameter estimation

(Can’t be bothered reading this whole post? Get the parameter estimation cheat sheet! ) Statistical textbooks often contain a paragraph like this somewhere toward the front: “The fundamental problem in statistical estimation is to choose an appropriate value for some population parameter, theta . The true value of theta is unknown as it is unlikely that […]

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Sample Size and Power Calculations Explained

sample size calculation

This kind of question about sample size comes up a lot: “I was told by my advisor to conduct a sample size / power analysis, because we want to state how many subjects we will need… I approached a statistical consultant at my university, and he told me that I needed to run a pilot study… I really […]

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