Top new questions this week:
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I’m wondering if anyone could recommend a diversity index to look at the differences in breeding bird territories between two sites. These are my data – the numbers represent the number of breeding …
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I thought that we assume i.i.d and therefore identically distributed (constant variance) over the line? But aren’t the below saying that technically the distribution changes from one X value to …
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I was writing an R Markdown for calculating measures of spread and was surprised to find that the IQR function does not use the IQR calculation I am used to using, …
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Consider a stick breaking process where we start with a large stick of length $x_1 \gg 1$. As long as the stick is larger than one, $x_k > 1$, we break the stick by, removing a piece of length 1 …
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For example, if I had a random variable X and knew it followed a normal distribution, I might write: $X \sim N(5, 10)$ What would I write if I’m trying to say that the distribution is unknown? $X \in \…
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I’m doing an analysis to see if having children is associated with treatment outcome. The children variable is categorical and takes values 0-7. When I dichotomise it into ‘children’ and ‘no children’,…
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I’ve been doing some reading on the topic of credible vs confidence intervals but unfortunately it feels like the more I read the more I’m confused. There seems to be a general sense or consensus that …
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Greatest hits from previous weeks:
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I am wondering how to choose a predictive model after doing K-fold cross-validation. This may be awkwardly phrased, so let me explain in more detail: whenever I run K-fold cross-validation, I use K …
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It seems that a number of the statistical packages that I use wrap these two concepts together. However, I’m wondering if there are different assumptions or data ‘formalities’ that must be true to use …
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They seem so similar. Are they the same thing but just referred to as different names?
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I understand that a stationary time series is one whose mean and variance is constant over time. Can someone please explain why we have to make sure our data set is stationary before we can run …
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I am trying to do a scatterplot to see the relationship between literacy and baby mortality. How do I know if literacy is my X axis and baby mortality is my Y axis, or the reverse? How do I …
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There is an old saying: “Correlation does not mean causation”. When I teach, I tend to use the following standard examples to illustrate this point: number of storks and birth rate in Denmark; number …
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The Pearson correlation coefficient of x and y is the same, whether you compute pearson(x, y) or pearson(y, x). This suggests that doing a linear regression of y given x or x given y should be the …
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Can you answer these questions?
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I am planning a study with three between conditions. Let’s say “Experimental group” vs. “Control group” vs. “Placebo group”. And I have a numeric outcome “DV” …
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Let’s say you have some dataset of observations which are either 0 or 1, and you want to estimate the mean and standard deviation / CI. This is straightforward to do. If the number of observations is …
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A decision boundary like in the picture.
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