Tagged Questions

1
vote
0answers
66 views

GLM experimental design issues for count data in landscape experiment

I am analyzing bird count data from surveys conducted each week (from Nov-April, when bird foraging most active near breeding cycle) for 6 years in 9 large experimental plots that are split amongst 3 ...
6
votes
4answers
334 views

What advantages does Poisson regression have over linear regression in this case?

I have been given a data set that contains the number of awards earned by students at one high school where predictors of the number of awards earned include the type of program in which the student ...
3
votes
1answer
259 views

GLM vs square root data transformation

I am currently analysing some pretty awful/awkward data on the abundance of fish under three different "Hydro-Regimes" (5 abundance measurements for each regime - Short/Medium/Long). The current ...
3
votes
1answer
211 views

Count explanatory variable, ratio dependent variable

I am having a little trouble coming up with a way of analyzing my data. If there is a short answer (i.e., "use logistic regression, dummy") you can just post that and I'll do some digging on my own - ...
3
votes
2answers
162 views

Best analysis for count data as response variable

I want to know what is the best way to analyze a data set where my response variable is count data and my explanatory variables are continuous variables. All my variables are not normally distributed. ...
18
votes
1answer
549 views

Why is the square root transformation recommended for count data?

It is often recommended to take the square root when you have count data. (For some examples on CV, see @HarveyMotulsky's answer here, or @whuber's answer here.) On the other hand, when fitting a ...
7
votes
2answers
519 views

Does using count data as independent variable violate any of GLM assumptions?

I would like to employ count data as covariates while fitting a logistic regression model. My question is: Do I violate any assumption of the logistic (and, more in general, of the generalized ...
3
votes
3answers
246 views

Can I put Log(Y) as a dependent variable in a count data model

I have count data passenger as Y. The data look like this, as many of the values are 1 (about 18%.) Does it make sense that I take a log of it, and take it as a dependent variable in a generalized ...
3
votes
1answer
416 views

How to get standard errors from R zero-inflated count data regression?

The following code PredictNew <- predict (glm.fit, newdata = Predict, X1 =X1, Y1= Y1, type = "response", se.fit = TRUE) produces a ...
2
votes
2answers
663 views

GLM model validation

When performing model validation and we are dropping the least significant explanatory variables until we find the optimum model where all remaining variables are significant, how does one go about ...
3
votes
1answer
221 views

Generalized linear models dispersion analysis

I was wondering, in relation to model selection for some count data I am looking at using poisson GLMs, would a high residual deviance (measure of dispersion) warrant switching to a quasi-poisson ...
1
vote
0answers
217 views

Help with R Zeroinfl model

I am carrying out a zero-inflated negative binomial GLM on some insect count data in R. My problem is how to get R to read my species data as one stacked column so as to preserve the zero inflation. ...
0
votes
0answers
210 views

Standard deviation when estimating a Poisson regression using R

I'm interested in plotting the estimator of the standard deviation in a Poisson regression. The variance is $Var(y)=\phi⋅V(\mu)$ where $\phi=1$ and $V(\mu)=\mu$. So the variance should be ...
3
votes
2answers
2k views

Whether to use an offset in a Poisson regression when predicting total career goals scored by hockey players

I've got a question concerning wheter or not to use an offset. Assume a very easy model, where you want to describe the (overall)number of goals in hockey. So you have goals, number of games played ...