Linked Questions
15 questions linked to/from Qualitative variable coding in regression leads to "singularities"
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To avoid the problem of perfect multicollinearity in binary variables, why is it fine to create separate variables for them in the linear regression? [duplicate]
I am reading Wooldridge's econometrics textbook. He provides the following example: Suppose we have a regression model relating wages to gender and education level.
wage = b0 + d0 female + b1educ + u
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How do get rid of (1 not defined because of singularities) in R? [duplicate]
I'm analyzing data in R, I'm trying to see how some variables affect test scores (Value) of different countries. In the data, since there is different time periods for different countries I need to ...
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Understanding dummy (manual or automated) variable creation in GLM
If a factor variable (e.g. gender with levels M and F) is used in the glm formula, dummy variable(s) are created, and can be found in the glm model summary along with their associated coefficients (e....
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What correlation makes a matrix singular and what are implications of singularity or near-singularity?
I am doing some calculations on different matrices (mainly in logistic regression) and I commonly get the error "Matrix is singular", where I have to go back and remove the correlated variables. My ...
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Removing attributes with few observations in R
I have roughly 15 variables / attributes characterizing 6k customers in my data set. As they are categorical I have transformed them into 1 attribute for each possible value (1-out-of-K coding). An ...
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Clear explanation of dummy variable trap [duplicate]
I have a confusion in multiple regression about dummy variable trap, so far I had seen tutorials explaining about dummy variable trap and multicollinearity but I'm unable to understand it fully.
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How to overcome Coefficients: (4 not defined because of singularities) [duplicate]
Stats is not my strong point but trying to run a regression. I'm aware that it happens because some of these variables are perfectly collinear. However, I do not know how to fix this? Any help would ...
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Regression based for example on days of week
I need a little help to move in the right direction. It's a long time since I studied any stats and the jargon seems to have changed.
Imagine that I have a set of car-related data such as
Journey ...
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Is there something called "mean coding" (like dummy coding & effect coding) in regression models?
When we perform a regression analysis with categorical predictors, we can use (1, 0), called "dummy coding". The coefficients in this case represent the deviation of the groups' means from the mean of ...
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What happens in a regression setting if you code n dummy variables for a categorical variable with n categories? [duplicate]
I understand the usual procedure to code categorical variables is to convert n categories into n-1 coded variables. For example, the categorical variable colour with levels red/green/blue could be ...
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Binary logistic regression: Wrong labels for the regression coefficients [duplicate]
I carried out a binary logistic regression using glm. Below you can see the (modified) output.
I included -1 to display all values, even the baseline which is ...
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Multicollinearity and the intercept term with categorial variables
We're given a regression equation with two dummy variables which are perfectly collinear. $$ y_i = \beta_1 D1_i + \beta_2 D2_i + e_i$$ where $ D2_i = 1-D1_i$. Can we estimate this model using least ...
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Predicting an output based on whether a variable is above or below a threshold
I want to create a linear regression model to predict an output that uses two different coefficients based on some threshold within the data. For example: df:
<...
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How can logistic regression have a factorial predictor and no intercept?
I tried a regression in the form ${\rm logit}(Y) = {\rm coefficient}\times X + 0 + e$, where $Y$ is a binomial variable and $X$ is a factor variable with $n$ levels. I noticed that removing the ...
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NA produced in linear regression model
I have read similar posts to this but my problem is not resolved by the answers given. I want to do a v simple linear regression to see if bite incidence is related to district, zone (vacc or control) ...