# Tagged Questions

A situation where the effect of an explanatory variable may depend on the value of another explanatory variable.

113 views

### How can I change the scores to make interaction effect in two way ANOVA significant?

My question is how to make an interaction effect become significant in two-way ANOVA. If my main effect A has an F value of F(1,80)=25.5 for example, and my main effect B has an F value of ...
181 views

### To exclude a main effect that is not of interest in ANCOVA, or not? [duplicate]

Possible Duplicate: Including the interaction but not the main effects in a model I have an experimental design with pretest and posttest. Two groups, experimental and control group. I am ...
121 views

### How to quantify moderation effect in an intervention study with multiple time points?

I want to measure a moderation effect between 3 continuous variable in an intervention study. I am using scores from self-report measures of masculinity, emotionality, and psychological distress. The ...
1k views

### Repeated measures ANOVA within and between factors

I have conducted repeated measures ANOVA, with 2 factors: One within factor (time, pre-post intervention) and one between factor (...
954 views

### Calculate standard errors: interaction between 2 factors, one of which has 3 levels in a regression model

I have the following model: $y \sim b_0 + b_1x_1 + b_2x_2 + b_3x_1x_2$. $x_1$ is a factor with 2 levels (0 and 1), and $x_2$ is a factor with 3 levels. I know that to calculate standard errors for ...
153 views

### Changing reference level on mixed model changes pMCMC value

I'm using an lmer on a set of continuous data. This post helped me a great deal when interpreting results, as I have two conditions and three levels as well, but I've run into a frustrating problem. ...
190 views

### Binary interaction terms using lmer

I am trying to create a model using the lmer function. The model will contain the continuous response term "Average.profit" and explanatory terms "Type", ...
308 views

### Effect of delivery mode of questionnaire (online/hardcopy) on results

I conducted a survey research where I have used two delivery modes for the questionnaire - online and offline (hardcopy mode). The survey questions measure perceptions of employees on certain ...
209 views

### 2-way interaction with only one main effect in the model - is it a “real” interaction?

I'm estimating a GLM with a continuous variable $X_1$, a dummy variable $X_2$ and the interaction term $X_1*X_2$. After my understanding, when interpreting the coefficient of $X_1$ you should assume ...
209 views

### What's the appropriate way to calculate an effect size when there is an interaction?

I have a regression model with two significant main effects and a significant interaction. I'd like to calculate an effect size for one of the main effects. I'm using the package ...
144 views

### How to tell if a continuous variable is associated with (treatment) change in another variable over time (one group, time 1, time 2)?

Hypothetical: I have treated a sample for depression and have (continuous) depression scores at intake (Y1) and at the end of treatment (Y2). I am wondering if motivation (X) at the start of therapy ...
264 views

### Measuring the moderating effect in my analysis?

I'm trying to analyze if the volume and sentiment (valence) of tweets has an effect on the sales of a product (in my case movies). The DV is sales with IV NumberOfTweets, Valence, DaysSinceRelease. ...
1k views

### Interpreting the regression output from a mixed model when interactions between categorical variables are included

I have a question about my use of a mixed model/lmer. The basic model is this: lmer(DV ~ group * condition + (1|pptid), data= df) Group and condition are both ...
2k views

### Joint model with interaction terms vs. separate regressions for a group comparison

After gathering valuable feedback from previous questions and discussions, I have came up with the following question: Suppose that the goal is to detect effect differences across two groups, male vs. ...
837 views

### How to interpret lower order interaction when higher order interaction is significant?

I have a question about the interpretation of lower order interaction terms in the presence of a significant higher order interaction effect. Suppose I have a 2 (factor $A$) $\times$ 2 (factor $B$) ...
166 views

### Group comparison: joint model vs. separate model, contradictory result

Any hint on this issue would be really welcome: The goal is to employ a two-country comparison analysis. When running two separate OLS regressions, one for each country, the coefficient of variable x ...
141 views

### Include interaction regressors separately?

I was taught that if I include a regressor in an interaction, then I should include it separately, too. That is, if I regress $y$ on $x_1 \times x_2$, then I should also include $x_1$ and $x_2$ ...
231 views

### te( ) interactions and AIC model selection with GAM in R

I'm working with a time-series of several years and to analyze it, I’m using GAM smoothers from the package mgcv. I’m constructing models where zooplankton biomass ...
426 views

### Can I use a difference score as my outcome variable (pre-post change) in a moderated multiple regression equation?

I am wanting to examine whether religiosity moderates intervention effects on stigmatized attitudes. Here are my variables: X = group (1 = experimental; 0 = control) Z = religiosity (14-item scale - ...
583 views

### How to calculate the interaction standard error of a linear regression model in R?

I have the following model and want to make a table with the interpretation of the interaction effects as suggested by Bambor and Clark in this paper. However, I have no idea on how to calculate the ...
79 views

### Testing interaction b/t group & longitudinal change for only part of the age range

I've fit a mixed linear model to some longitudinal data. I'm interested in the differences in patterns of decrease in the dependent variable according to group status, and my hypothesis particularly ...
741 views

### Testing for moderation with continuous vs. categorical moderators

I am testing an interaction effect where X and Y are continuous variable and M (Moderator) is a categorical variable (effects coding +1, -1). I have no clue about how to do a post-hoc probing of ...
46 views

### How to interpret an insignificant main effect that became significant at the presence of interaction effects in moderated regression analysis? [duplicate]

Possible Duplicate: What if interaction wipes out my direct effects in regression? I did hierarchical regression analysis on my data due to having interaction effects in my research model. ...
848 views

### How to cope with multicollinearity and interactions between IVs in generalized linear models?

I have made a generalised linear model with a single response variable (continuous/normally distributed) and 4 explanatory variables (3 of which are factors and the fourth is an integer). I have used ...
2k views

### Cox proportional hazard model and interpretation of coefficients when higher case interaction is involved

Here is the summary-output of the Coxph-model I used (I used R and the output is based on the best final model i.e. all significant explanatory variables and their interactions are included): ...
1k views

### How should I interpret the interaction term in a Cox proportional hazards model?

How should I interpret the following interaction term of 2 continuous predictors in the output of a Cox proportional hazards model? The Hazard ratio for the interaction of X and Y is >1, which means ...
374 views

### Excluding the components and only including the interaction term in a logistic regression? [duplicate]

Possible Duplicate: What if interaction wipes out my direct effects in regression? We have a question regarding a regression we are working on. We have two dummy variables, net income (If ...
484 views

### Interaction Terms and Logit Models

I have read the previous discussions on interaction effects and main effects, and I have a question on the subject. I am running a destination choice model (multinomial logit), and I have one ...
68 views

### GWAS and Statistical theory - does the likelihood of a detectable main effect decrease with complexity?

I've been wondering recently about the difficulty of detecting statistically significant results from, say, genome-wide association studies. In these studies, many - ($10^{8}$) for example- ...
503 views

### Following up a three-way interaction found with (mixed) model comparison

I hope this isn't a silly question, I'd like some advice on following up a threeway interaction in a mixed effects model. I've been building my models incrementally, like this: ...
8k views

### How to interpret main effects when the interaction effect is not significant?

I ran a Generalized Linear Mixed Model in R and included an interaction effect between two predictors. The interaction was not significant, but the main effects (the two predictors) both were. Now ...
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### How to test and examine interaction effect in 2 by 3 by 6 mixed ANOVA design?

Background: I have two groups of children - one group with normal hearing and one with permanent hearing losses - call them NH and PHL. Each child has had a hearing test, consisting of 6 different ...
56 views

### Interaction term change the significance of the main effect variable [duplicate]

Possible Duplicate: What if interaction wipes out my direct effects in regression? I am just wondering why would adding an interaction term to the regression model change the main effect ...
1k views

### How to compute significant interaction estimates when main effect is not significant?

I have a linear model of a dependent variable, $y$, with two predictor variables, year and site, and their interaction, with year being numeric and site categorical. The main effect of year is not ...
2k views

### What is a valid post-hoc analysis for a three-way repeated measures ANOVA?

I've performed a three-way repeated measures ANOVA; what post-hoc analyses are valid? This is a fully balanced design (2x2x2) with one of the factors having a within-subjects repeated measure. I'm ...
6k views

### Do all interactions terms need their individual terms in regression model?

I am actually reviewing a manuscript where the authors compare 5-6 logit regression models with AIC. However, some of the models have interaction terms without including the individual covariate ...
135 views

### Determining where no correlation exists

I need to determine at what value of a variable mictrb there would be almost no correlation between two other variables: ...
134 views

### Comparing drug effects in different conditions

What is the ‘correct’ way to compare the effect of a drug in different conditions? For example, if I have conditions a, b, c and d, where there are different numbers of ‘control’ and ‘drug’ cells in ...
1k views

### Mediator versus moderators - not sure which is more appropriate

I am undertaking a study which has the following aims: The main aim of the current study is to investigate the effects of food messages about the healthiness of foods on actual food intake. ...
2k views

### How to interpret two-way interactions in Linear Mixed Effects modeling?

I've fit a Linear Mixed Effects model to some "accuracy" scores for a study with rats. The fixed effects are TrialNumber and ...
307 views

### What is the effect size for the interaction of a 2X2X2 contingency table?

I am computing the interaction in several 2X2X2 tables (i.e. in each case, I have eight frequencies), see for an example this file. I have two predictors (low vs high 'threat' and low vs high ...
39 views

### Can the influence of a different factor on a known effect be analyzed directly?

If I am trying to analyse wether a known effect is inhibited by another factor, is it a fallacy to analyse the influence of the factor on the effect size directly? I.e. can I just use a statistical ...
536 views

### Moderated regression for categorical, within-subjects variable

I am planning to run a moderated regression on my dataset with two IVs. One of them is a straightforward interval data-type, between subjects IV (e.g. anxiety level). The other is a categorical ...
173 views

### Categorical variable with a lot of levels and interaction

Suppose we have a categorical variable $X_1$ with $100$ levels. Should we not test interaction between $X$ and some other variable $X_2$? Because if, for example, $X_1(3)*X_2$ is not significant ...
378 views

### Interaction term as a dependant variable in LMM with R

In a longitudinal study, two groups of subjects have been measured over a period of two years at 6 months intervals. During these measurements subjects have been assessed with a series of $k$ measures ...
302 views

### How to follow up a 3-way interaction with one continuous variable in F-test fixed effects in mixed model

In the Estimates of Fixed Effects SPSS-table, I don't understand why certain parameters are set to zero an just a dotted line appears (because they are redundant according to SPSS). Moreover, I don't ...
3k views

### How to perform post-hoc comparison on interaction term with mixed-effects model?

I’m working on a data set in order to evaluate the impact of drying on sediment microbial activities. The objective is to determine if the impact of drying varies among sediment types and/or depth ...
576 views

### Cohen's d for 2x2 interaction

I have a significant 2x2 interaction in a between-subjects design. I would normally report omega-squared as my effect-size measure, but I've been asked to provide Cohen's d instead? Can Cohen's d be ...
I want to interpret an interaction. Usually a conditional regression analysis is done with 1 SD below/above the mean (see Aiken & West, 1993, p. 18). My result is a contrast with $p=.068$ if I ...