A contrast is a linear combination of parameters or parameter estimates, with the coefficients in the linear combination known. Often used to test focused hypotheses.

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Is the Scheffé test of contrasts the “best-case” for post-hoc tests?

I am reading through Explaining Psychological Statistics, 4th Edition and am stumped after the following passage: Scheffé (1953) understood that the best anyone can do when creating a complex ...
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17 views

Statistics, R: Build linear regression model with differently contrast-coded variables

I want to build a linear regression model where I predict a mean of a group of participants (how they rate something on average). Predictors should be age (continuous) origin (deviation coded, each ...
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14 views

Planned contrast through factor-based vs. model-parameter-based approach

I have two questions concerning planned contrasts: I would like to know how factor-based contrasts (obtained through an interaction term) compare to model-paramter-based contrasts (obtained by ...
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27 views

Logistic regression with 2 predictive variables

I need some advice for choosing the correct model. I have 3 binary variables: Risk (0 = the person doesn't take financial risks, 1 = the person takes financial risks), gender (0 = female, 1 = male), ...
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24 views

Using contrasts in Poisson regression

The question is about using contrasts in regression analysis (here, Poisson regression with robust error variance). We have devided the participants in our sample into 6 groups, according to their ...
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1answer
29 views

Advantage/acceptability of using contrast codes to conduct pair-wise comparison vs. t-test on subset of data?

I conducted a study with three conditions (A, B, and C) and I want to test the difference between A and C. My default approach would be to run a t-test (or its equivalent) on a subset of the data (...
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13 views

Permutation test for repeated measures (in time)

I have the measurements of a quantity, observed every day for 60 days Usually, this quantity is really near to 0, apart from 3 days where it is (significantly?) greater than 0 I thought it would be ...
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1answer
23 views

Repeated measures ANOVA contrasts

I'm running a repeated measures ANOVA with a 3-level DV. Now what I've read is that you only look at the post-hoc test if the within-subject (overall) effect is significant. What about the within-...
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22 views

Application of Anova/Manova

I have a dataset providing information about head and leg injuries for drivers and passengers . The dataset contains the following variables Head.IC: Head injury criterion(number) Chest_decel: Chest ...
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13 views

Anova and contrast

How do we use ANOVA and Contrast to compare multiple dependent variables with multiple independent variables in R. Have watched few videos in you-tube but am really confused. How do I compare ...
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10 views

Compare the coefficients of two independent variables within a model, representing 2 diff independent variables are statistically different?

I'm trying to show that two coefficients within a model are statistically different from each other. These variables measure two similar, but different variables, price increase and price decrease. ...
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1answer
72 views

condition specific differentially expressed genes

I have log2 transformed gene expression data set. ...
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19 views

How to set sum contrasts for unbalanced factors

Let's say that I have a model where the response time depends on accuracy (0/1, coded either as categorical or numerical) and another categorical variable (pres: idem/diff), both interacting with the ...
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2answers
47 views

Test for one coefficient doubled another one?

I want to run a regression in order to test ( thinking of the $t$-test ) the null hypothesis that one coefficient ($b_2$) is twice another coefficient ($b_3$), so $b_2= 2 b_3$, The variable for $b_3$ ...
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7 views

Control the composition of scored data based on certain variables

So imagine you had some sample with the following demographic breakdown: Gender: 30% Female 70% Male HHI: 30% Less than 50K/year 50% 50K - 100K 20% More than 100K and you want to build a ...
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27 views

Confused about F-contrast and F-test in statistical software

Let's say I have an estimated parameter $\beta$ from a general linear model for 2 subject groups (with the $\beta$s corresponding to their means). If I wanted to do a two sample t test in a ...
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15 views

How to specify these contrasts in R

Can anyone tell me how to create the following contrasts in R? ...
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26 views

Linear mixed effects models for longitudinal, unbalanced data

I want to use linear mixed effects models (lme4::lmer) for the selection of features (dependent variables, >1000) on significant differences between specific groups ...
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1answer
51 views

Mean Differences in Poisson Regression

I performed a Poisson regression. My dependent variable is number of days and my independent variables are all binary indicators (e.g. facility = facility1 facility2, facility3 and severity = extreme,...
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27 views

More than three independent contrasts in PERMANOVA

I try to create more then three independent contrasts in PERMANOVA with 4 factors without success. I need to use all possible pairwise combinations of factor levels in my contr2df object. There are ...
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14 views

Changing contrasts for AOV doesn't seem to change anything?

My data set acidity.data has 10 observations each for 3 regions. The regions are listed in the Group column as ...
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33 views

User defined contrast coding with 2 categorical and 1 continuous predictor

I would really appreciate if someone could confirm that the contrast matrix that I defined with the glht package for my model is correct and that the continous ...
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46 views

Beta regression using GAMLSS: how to do post-hoc contrasts?

I have compliance rate data [0,1] from a mixed design study, which examines compliance rate over time for people receiving different types of incentives. I looked this up and thought that the beta ...
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24 views

Factor in linear mixed model is significant, but none of the contrasts?

So I have a linear mixed model with two fixed factors, let's call them A and B, A has three levels (A1,A2,A3) and B two (B1,B2). There is also a random effect, let's call it subject. Over likelihood ...
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1answer
81 views

Defining a contrast matrix to test the null hypothesis $H_0: \beta_5=\beta_6=0$

In the book Applied Longitudinal Analysis, 2nd Edition there is an example in the chapter "Marginal Models: Generalized Estimating Equations (GEE)" in "Muscatine Coronary Risk Factor Study" sub-...
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44 views

Contrasts for hypothesis test in linear mixed model with repeated measures in R

I have data from an experiment in which we measured electromyographic (EMG) activity of 4 muscles before and after an emotion induction, in 71 participants. I have my data in long format, so I have ...
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11 views

Testing time trend theories using contrasts

I am planning analyses for a study in which I have 5 different groups who take measures at four time points. I plan to conduct my analyses in a two step process. First, I want to find which theory/...
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47 views

Planned contrasts in ezANOVA

I have a data set that is 3 x 5 and I can easily run a repeated measures ANOVA using ezANOVA in R. I now wish to have planned contrasts going into the ANOVA. The data consists of one control ...
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6 views

Doubts regards the contrast between two samples to analyze their expected values

I have this two samples: pob1<-rchisq(90,12) pob2<-rchisq(50,7) For making a contrast to see whether if I can guess that their expected values are equal or ...
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8 views

Making a contrast of two samples

Having this pob1<-rchisq(90,12) pob2<-rchisq(50,7) How can I make a "contrast" to see if I can guess that both of their expected values are equal against ...
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22 views

Interpretation of orthonormal contrasts in ANOVA/regression

Is there an intuitive substantive or geometric interpretation of regression coefficients associated with categorical predictor variables coded with orthonormal codes? For a simple example, say we are ...
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1answer
74 views

How to preserve order of factor levels in R [closed]

I have an unbalanced longitudinal data for glucose levels of some patients coming to a hospital. My data looks like id, date, glucose_level. As I want to find the ...
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1answer
75 views

Contrasts in ANOVA in R

I have conjured up a dataset here: ...
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42 views

Appropriate test for two test groups, one control group and binary outcome

I have the following problem: We send our Clients an email and offer them some new product. Let's say we want to test 2 email designs. Additionally, we need a control group, since some of the clients ...
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19 views

contrast testing in binomial GLM when variance = zero

I am trying to use GLM (family = binomial) to to test for differences in gene frequency among treatments. The data is binary (gene is present or absent). Its a simple one way model,but with quite a ...
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21 views

Calculate contrast given the estimate and standard deviation

I am analyzing results for a before-after control-impact experiment on species richness. I've used the 'vegan' package to calculate species richness using species accumulation curves, using the ...
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30 views

How to construct contrasts for a linear model with interactions?

I have trouble figuring out how to set up contrasts for a linear model with interaction terms. In the following example, how do I construct contrasts so that I test for the differences of species A - ...
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56 views

Complex Factorial Manova in R/SPSS

Hello I have been struggling for many days with this problem. The situation and data set are following. The data set comes from an experiment that asked subjects (ID) to compare several CVs on ...
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41 views

Occupancy analysis in Rmark: how can I calculate contrasts for BACI (Before-after-control-impact) experiment?

I'm analyzing presence/absence data using Rmark occupancy analysis (i.e. Rmark is the package which runs Program MARK in R). This is for a BACI (before-after-control-impact) design and I want to ...
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74 views

Zero-inflated Poisson regression: how can I calculate contrasts for BACI (Before-after-control-impact) experiment?

I am analyzing count data with a lot of zeros and found that although the data do not fit a poisson glm, they fit the zero-inflated poisson (ZIP) regression significantly better than the standard ...
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32 views

what are the consequences if a contrast is non-orthogonal?

everywhere I read about orthogonal contrasts. I know what they are, but I see nowhere why it matters if they are orthogonal or not. What are the consquences? Thank you!
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21 views

Strong differences in p-values depending method used to set contrasts with TukeyHSD in multcomp

I am currently running multiple comparisons following ANOVA. For this I want to set my own contrasts in TukeyHSD to exclude comparisons not of interest. So the first thing I did is test whether my ...
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61 views

How do I report Helmert contrast when running ANOVA?

I am a German student, so my English might not be perfect. Sorry for that. I would like to know how I do report Helmert contrast. I ran a two-way ANOVA and I wanna write down my contrasts in my thesis ...
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5 views

Sum Squares not adding up with testFactor

For some unknown reason the SS for the orthogonal contrasts I created with testFactor in the phia package do not add to the SS for the factor. Any ideas? Here is how I created the contrasts: ...
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23 views

contrast mean difference between intervention and control group

I'm studying a case of a quasi-experimental design, and have two groups. The Intervention Group and the Control Group. An answer for each individual was measured before and after the intervention (...
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13 views

how to (not) plot all pvals if many contrasts are done

I have run an ANOVA and then a Bonferroni test, using 8 groups. Therefore, the significant pvalues are many and showing them in a plot is messy. How would you recommend to approach this ...
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27 views

Compare one level vs the others in regression

we have a set of esclusive mutations on a set of genes. We would like to estimate the influence of such mutations on a certain syndrome. Our main problem is how to model the comparison between ...
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2answers
180 views

Why do some regression estimates differ by a change of sign, but others don't, when I change reference level?

Suppose I have a continuous outcome y and two factorial predictors, each with two levels. One of my categorical predictors, drug,...
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0answers
34 views

Orthogonal contrasts in a logistic mixed-effects model with unbalanced dataset

I have a dataset containing a dichotomous outcome variable Y, and 3 independent variables: ...