The logarithm of a number is the power to which the base must be raised to get the number.

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26 views

multiplying an outcome and predictor values by ten flips the sign of an effect size when log transformed. WHY?

I have a model, y~ x1 + x2 + x1*x2, where y and x1 are strongly correlated and ...
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12 views

How to use ln-transformation with loads of zeroes?

I came across a method of ln-transforming exogenous variables in non-negative data sets with loads of zeroes in a lecture. With the method proposed, one simply ln-transforms the variable in question ...
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82 views

Is there something clever I can do with a log of a sum?

In something I'm working on, the expression $$\lim_{n\rightarrow\infty}\exp\left(-\frac{1}{n}\log\left(\prod_{i=1}^{n}X_{i}+\prod_{i=1}^{n}Y_{i}\right)\right)$$ came up, in which all $X_{i}$ $iid$ and ...
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2answers
51 views

How do I change logarithmic scaled data to linear scaled data?

I am using decibels for my research, and I was told by someone that I cannot perform any statistical analyses on these measurements other than basic descriptive statistics because the data are ...
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1answer
203 views

How can I recognize when I must apply “log transformation”?

I have some time series - http://ww2.coastal.edu/kingw/statistics/R-tutorials/simplenonlinear.html In this article author try to use log transformation for pressure data. How can I recognize that ...
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38 views

How to interpret log-transformed predictors in probit regression?

I am running a probit model with several continous and one log-transformed predictor (firm size as total assets). I am unsure how to interpret the coefficient of -0.341 on that variable. I used the ...
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1answer
49 views

Back transformation of log10 transformed data in SPSS

I have transformed my quantitative variable by using the log10 function in order to run some parametric tests (ANOVA) but when I want to make pairwise comparisons ...
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1answer
48 views

What is the difference between a $\log_{10}$ and logit transformation?

What is the difference between a $\log_{10}$ and logit transformation? I have tried to find the answer elsewhere but cannot find a strict distinction.
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1answer
108 views

Why don't log-likelihoods lead to log(0)?

How do log likelihoods function in practice? I seem to oscillate between understanding this and not understanding this (which most likely means I've never understood it). When you take log( P( X | Y ...
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10 views

Variance of the logarithm of a binomial distributed random variable

What is the variance of $\log(1+X)$, where $X \sim Bin(n,p)$. I am looking for an approximate solutions depending on n and p. I have tried Taylor expanding the logarithm, but it didn't lead to a ...
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1answer
54 views

Rule of thumb for using logarithmic scale

When I am given a variable, I usually decide wether to take its logarithm based on gut feeling. Usually I base it on its distribution - if it has long tail (like: salaries, GDP, ...) I use logarithm. ...
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13 views

goodness of fit log transformed vs not log transformed

I have a relationship of two variables which is somehow log shaped. Now, I establish two models for this dataset, for one I log transform the dependent variable: ...
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1answer
52 views

log-log vs. normal plotting for showing linear dependency

I have a set of data, basically measuring the running time of an algorithm against some gathered input. This is the summary of data: ...
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1answer
39 views

GLMM with Gamma distribution vs. Gaussian distribution with log transformation

Is there really a difference in result if I use a GLMM with Gamma distribution vs. a model with a Gaussian distribution with log transformation? If so, how do I choose between the two methods? See ...
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1answer
31 views

transforming exchange rate and inflation rate

I am testing some variables in percentage (exchange rate, inflation, and GDP growth rate), and I am a bit hesitate whether it is better leave them as percentage or transform them into log values. ...
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1answer
52 views

Interpretation of log(1 + x) transformed predictor

Interpretation of log transformed predictor neatly explains how to interpret a log transformed predictor in OLS. Does the interpretation change if there are 0s in ...
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1answer
36 views

Large Increase in Naive Bayes Accuracy results in decrease precision?

I am trying to classify (37 possible classes) a dataset that has 9 features and 900,000 occurrences. I have tried a couple different algorithms but the one that gave the lowest logarithmic loss was ...
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1answer
37 views

Log linear model interpretation - % Contributions?

I know that for log-lin models the interpretation for the coefficiente is this one, that is: Coefficientsâ‹…100 have a semi-elasticity interpretation: for a 1 unit change in x, you get b*100% change in ...
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1answer
376 views

How to transform negative values to logarithms?

I would like to know how to transform negative values to Log(), since I have heteroskedastic data. I read that it works with the formula ...
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1answer
61 views

Should I use the mean difference or mean ratio for a t-test?

I have a quantitative variable (medication dose) that is paired: dose of medication before surgery and after surgery for 76 patients. I was under the impression that I should calculate the mean of ...
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91 views

How to backtransform data that has been log transformed in order to report raw values for ease of interpretation?

I have run some lme4 analyses on reaction time data in R, with RT being the main outcome variable of interest, which I first log transformed due to non-normality ...
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23 views

Natural logarithm transfomation and zeroes [duplicate]

I am using Stata 13 to estimate a simple regression. Given a rather positive skew of a few of my covariates, I figured to ln-transform the variables. However, I have a substantial amount of zeroes in ...
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44 views

How to treat missing values in a regression?

I have used the logarithmic form of wage as my independent variable in Stata. However, it contains missing values. Should I replace these with 0 or let them be?
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97 views

Log Transformation

I am planning to run a 2x2x3 repeated measures ANOVA on reaction time data pre and post treatment. However, my data is skewed and I wanted to do a log transformation but have few questions. Can I ...
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13 views

Meaning of growth of log-transformed variables [duplicate]

I am dealing with the transformation of the variables for my master thesis (a panel dataset with a xtabond2 model). The analysis focuses on growth rates, so my co-director told me to transform the ...
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1answer
100 views

Cohen's D: Should I use raw data, log transformed data or back transformed data?

I am a doctor and right now I am doing medical research. I have some questions about cohen's d. I try to research it on the internet but it seems there is not much answer to this question. My project ...
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36 views

Interpreting level-level models with units in %

I have a model where the dependent variable is GDP growth in (%). I regress this on a my variable of interest, wine sales ($). Do I have a level-level model? Growth = a + Bwine + u How do I ...
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26 views

Interpretation of log transformed coefficients, OLS regression [duplicate]

I have a question about how to interpret or use the result of an OLS regression w a log transformed DV. Due to non-normal distribution of the Dependent variable, I used a log10 transformation to coax ...
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29 views

lin- log model with unbalanced time series

I want to compute the following regression: lm(y~x+log(TAF) from observation nr. 100 to observation nr.300, where x is a controll variable. Now the problem is ...
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1answer
575 views

Interpretation of marginal effects in Logit Model with log$\times$independent variable

I am totally confused by statistics and I would be glad if you could help me. I have a difficulties to interpret marginal effects in logit model, if my independent variable is log transformed. I ...
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29 views

Why small values produce undulating densities when ploting logarithm of a loguniform prior (in R)?

I am using a program that draws random values in a log-uniform distribution let say between 1 and 100. When I plot the density of the produced values with R it looks like a log-uniform distribution ...
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17 views

Medians of logged fold changes.

So I have a set of measurements from several studies consisting of fold changes between log2-transformed values between two groups, each calculated using the formula ...
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1answer
101 views

Advantages of taking the logarithm to minimize the likelihood

In regression/classification problem, we are often interested in minimizing a cost function with respect to the parameters of the model. In many cases, the cost function is the negative likelihood. To ...
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49 views

Why not just use log for regression if it improves r-squared?

theoretical question here: Say I have a model, $y = \beta_0 + \beta_1 x + u$ and it gives an $R^2$ of 0.02 Suppose, I re-estimate the model with $y = \beta_0 + \beta_1\log(x) + u$ which gives an ...
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54 views

What happens if I square the variable in my log in OLS regression?

Say I have a model: ln y = B0 + B1(x1) + B2 ln(x2) + u and the B2 estimate I get is 0.5 If I change the model to be ln y = B0 + B1(x1) + B2 ln(x2^2) + u the estimate will change to 0.25, but why ...
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52 views

mean of log or log of mean

I'm interested in how indiviudals are influenced, by other individuals they are connected to. So mean values of connected individuals are included in a linar regression model. Some of my variables are ...
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241 views

Percent change interpretation in log-transformed regression: Percent change from what?

I am dealing with a regression model where both the DV and IV are log-transformed. I have found this explanation of how to interpret the effects (both in the Cross-Validated hyperlink and in ...
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48 views

Interpreting standardized log coefficients in OLS

I used the log for my dependent variable as well as for some independent variables. Then I standardized all variables. Now I'm not sure how to interpret the coefficients. Are the log and non loged ...
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45 views

log transformation decreased model fit?

I just wondered why logged income (independent variable) decreased my model fit for OLS regression. My income distribution is skewed to the right and I am trying to transform the data. I separately ...
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116 views

Interpretation of impulse response functions with variables in logs

I am looking at the relationship of several macroeconomic variables, all in natural logs, using Vector Error Correction (VECM) models and Impulse Response Functions with a standard Cholesky-type ...
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3answers
89 views

What is the statistical logic behind using logarithms in analyzing threshold elevations?

In my field, a lot of experiments are done comparing performance between a baseline condition, and a more difficult condition. Typically, thresholds are measured at each of these two conditions, and a ...
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1answer
152 views

Log form of variables and descriptive measures

Because of larger values of variables, I did a log- transformation in my dataset. Now I want to give a descriptive table regarding my variables like mean, max, min, median, skewness, kurtosis. Can I ...
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4answers
745 views

What are the formulas for exponential, logarithmic, and polynomial trendlines?

In creating linear trendline, I used the following formulas: $$y=mx+b$$ $$m = \frac{n\sum(xy)-\sum x \sum y}{n\sum x^2 - (\sum x)^2}$$ $$b = \frac{\sum y- m \sum x}{n}$$ and this for the R-squared: ...
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31 views

Interpretation of logged term in logit (generalizing previous answers)

I have a logistic regression model, where one of my variables is logged. It is of the following form: $\ln(\frac{p}{1-p}) = B_1\ln(X) + B_2Y + ... + \epsilon$ , where $\epsilon$ is an error term. I ...
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1answer
42 views

Value of logarithmic form

I'm having trouble grasping the viability/value of log'ing a dataset. This post mentioned that it's used to normalize (read: shrink extremes of) a dataset and make it easier to fit a curve. But, ...
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32 views

Semi partial correlation importance variables

I have some SAS code that is used to calculate the importance of variables using semi-partial correlations: ...
2
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1answer
407 views

do logs modify the correlation between two variables?

I am applying logs to two very skewed variables and then doing the correlation. Before logs the correlation is 0.49 and after logs it is 0.9. I thought the logs only change the scale. How is this ...
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1answer
40 views

Interpreting a logarithmic difference as an error

This is a fairly simple question but I can't figure out which one is the correct approach. In astronomy it is usual to report age values via their base 10 logarithms instead of the actual value. So a ...
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20 views

How to account for data taken at $t=0$ when using $\log(t)$ in the model? [duplicate]

I have a data set with four observations consisting of the variable $Y$ measured at time $t_0=0$ and at times $t_1, t_2$ and $t_3$. I would like to fit the following model: $$\log(y_j) = \alpha + ...
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1answer
84 views

Looking for a layman's explanation of how to manually calculate log odds?

I will start that I am not as math oriented as I would like to and could use a layman's / non-staticians explanation walk through of how to calculate the log odds. I am reading Hosmer, Lemeshow, and ...