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A lognormal distribution is the distribution of a random variable whose logarithm has a normal distribution.

2 votes
Accepted

General way to calculate or think about non-linear but monotonic (?) transforms of random va...

It sounds like you want the formula for the density transformation under a monotonic function. If you start with a continuous random variable $X$ and you define the random variable $Y=f(X)$ using a s …
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2 votes

Interpretation of linear mixed model with log(x+1)-transformed response variable

Short answer: Back-transformed coeffient estimator is biased, and not a good estimator. Back-transformed confidence interval is valid, but sub-optimal. Longer answer: Since you have not included a …
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3 votes
Accepted

Difference between log normal probability density values

In this context $\log$ means $\ln$ (i.e., a logarithm with base $e$), so the second website is probably not claiming that it is a logarithm with a base of ten. For a logarithm with base ten you would …
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2 votes

Showing the expectation of a lognormal AR(1) process

Your basic reasoning is correct, but your expression for the variance of the process is wrong. If we let $Z_t \equiv \log Y_t$ then the process $\{ Z_t | t \in \mathbb{Z} \}$ is a standard Gaussian $ …
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1 vote

Estimate population mean from sample with known distribution

If you have $n=100000$ sample values then the two methods should give you estimated values that are very close to one another. Since you haven't supplied your calculations I cannot say what went wron …
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3 votes

How do I know when to use log-transformation?

It is not really anything to do with trying to get a normal distribution (and in most models, you don't really need to transform variables to make them normal anyway). We generally apply a logarithmi …
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3 votes

When is it OK to write "we assumed a normal distribution" of an empirical measurement?

This largely depends on the robustness of your inferences to errors in the distribution When you are dealing with quantities that are either directly observable, or for which there is some close estim …
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1 vote

Weighted average distribution

The numerator in your expression for $R_t$ is the logarithm of a weighted sum of lognormal random variables. The distribution of this quantity is complicated, but it has some known approximations (se …
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1 vote

Log-normal returns

Since the returns involve changes in the stock price over consecutive time periods, the answer to your question depends on the joint distribution of the stock price over time. Since you have only spe …
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2 votes
Accepted

Expectation Value of a Product of Many IID variables

It appears that you are confusing the random variables $X_1,X_2,...,X_N$ with their expected values. As presently defined, the value $S$ is not a random variable at all; it is a constant (and so the …
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3 votes
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PDF of a log-normally distributed variable after tangens hyperbolicus transformation

The hyperbolic tangent function $\tanh$ is a strictly increasing function, so it is quite simple to get the CDF of the random variable $Y$. I am going to give a more general answer that what you are …
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10 votes
Accepted

Intuition for why mean of lognormal distribution depends on variance of normally distributed rv

The intuition for this result comes from the fact that the exponential function is a strictly convex function. When you then impose a convex transformation on the random variable $X$, the positive de …
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