Linked Questions

89
votes
7answers
33k views

What is the benefit of breaking up a continuous predictor variable?

I'm wondering what the value is in taking a continuous predictor variable and breaking it up (e.g., into quintiles), before using it in a model. It seems to me that by binning the variable we lose ...
25
votes
3answers
6k views

How to model this odd-shaped distribution (almost a reverse-J)

My dependent variable shown below doesn't fit any stock distribution that I know of. Linear regression produces somewhat non-normal, right-skewed residuals that relate to predicted Y in an odd way (...
18
votes
3answers
22k views

Continuous dependent variable with ordinal independent variable

Given a continuous dependent variable y and independent variables including an ordinal variable X1, how do I fit a linear model in R? Are there papers about this ...
17
votes
1answer
25k views

How to choose between ANOVA and ANCOVA in a designed experiment?

I am conducting an experiment which has the following: DV: Slice consumption (continuous or could be categorical) IV: Healthy message, unhealthy message, no message (control) (3 groups in which ...
9
votes
4answers
5k views

Extending logistic regression for outcomes in the range between 0 and 1

I have a regression problem where the outcomes are not strictly 0, 1 but rather in the range of all real numbers from 0 to 1 included $Y = [ 0, 0.12, 0.31, ..., 1 ]$. This problem has already been ...
13
votes
2answers
5k views

Tobit model explanation

We have 100 participants in two groups, $n=50$ in each group. We used an assessment of ability of basic functioning at 4 time-points. The assessment comprises 6 questions, each scored 0 – 5. We do not ...
7
votes
1answer
4k views

Justification for low/high or tertiary splits in ANOVA

I have two groups of participants and they all took the same measurements. When I perform a median split on one of the measurements to test my hypothesis about an interaction, the dependent ...
11
votes
1answer
4k views

Dealing with regression of unusually bounded response variable

I am attempting to model a response variable that is theoretically bounded between -225 and +225. The variable is the total score that subjects got when playing a game. Although theoretically it is ...
12
votes
1answer
6k views

Logistic quantile regression – how to best convey the results

In a previous post I’ve wondered how to deal with EQ-5D scores. Recently I stumbled upon logistic quantile regression suggested by Bottai and McKeown that introduces an elegant way to deal with ...
6
votes
2answers
3k views

extremely left-skewed response variable - how do I model this dataset?

This is a histogram showing my response variable. The response is # (or proportion? or percent?) of aphids eaten off of cards in fields, to model predation by natural enemies. Predictors: fixed ...
2
votes
1answer
3k views

Effect of two demographic IVs on survey answers (Likert scale)

I have 4 questions in a survey with Likert-style answers (i.e. 1–5) – and the participants have also answered the demographic questions (country and study-years) – which test do I need to find if the ...
4
votes
2answers
263 views

Is a pretest-posttest ANOVA with quartiles of pretest efficacy as an IV reasonable?

I'm reading a paper here that does an analysis that I find odd, and I'm wondering whether it is reasonable to do what they are doing. The paper isn't available online but I think I can describe the ...