Questions tagged [ancova]

Analysis of Covariance. This is really a special case of multiple linear regression, used in ANOVA-like settings with some continuous covariates in addition to the categorical ones.

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Factor analysis when I have mixture of continuous and dichotomous variables

I am trying to determine if there is a significant difference between two groups for a single continuous variable while accounting for baseline differences in dichotomous variables in each group. To ...
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How do I perform and interpret an Ancova/Poisson Regression, with multiple covariates and possible interactions?

I am researching how recovery time of trees after tropical wildfires differs between South America, Africa and Australia, using R. For this, I am using a Poisson regression. First I checked if there ...
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Significant interaction between covariate and factor in R

I have a dataset of subjects age, test score, and group (each subject belongs to 1 of 3 groups, let's say A, B, and C). Only the 'group' is categorical. The sample size is different between the groups ...
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Two-group “ANCOVA” with Theil-Sen?

("ANCOVA" might typically refer to using at least three groups. In what I do, I am always comparing two groups, and that is what I mean throughout this question.) I know how to do ANCOVA via OLS ...
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If interested in common a trend in multiple groups, can I pool all the data and run a correlation rather than an ANCOVA?

Dear CrossValidated Community, I have three groups, each of which has some biological data I'll call X, and I am interested in whether X is correlated with their treatment response, Y. Thus far, I ...
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How to interpret the interaction term in an ANCOVA model

Just looking for some help on my ANCOVA analysis. My study is basically looking at the difference in variables at 12 weeks in an exercise group and a control group. In figure 1 included as I ...
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Anconva or Anova for multifactor analysis

I have non-normal plankton community data, where rows are sites and columns are species (dependent) and a few factors. I want to check the influence of season on community (dis)similarities but am ...
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Discrepancies in robust ancova calculated in R with the WRS2 package vs by hand

I've conducted a study where participants in 2 groups (Control and Experimental) completed three scales (NJ, A, and D) at two time points (T1 and T2). I'm running ANCOVAs with the T2 responses as my ...
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Why is the Tukey method not appropriate for covariance analysis when estimating treatment effects?

In the book 'Applied Linear Statistical Models' chapter 22 it states that the Tukey method is not appropriate for covariance analysis. The context is in estimation of treatment effects. Instead, when ...
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Interpreting repeated-measures oneway ANCOVA

I have a question on how to run a repeated-measures oneway ANCOVA. I have only one within-subjects factor (time) and I am interested in how a construct changes from T1 to T2. I would also like to add ...
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Comparing two correlations/regressions with a repeated variable?

apologies this is possibly a repeat question but I have done a fair amount of googling and the answer is not obvious to me. I have two variables each measured on different days. Say a_day1, a_day2, ...
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Levels of a random effect coincide with values of covariates

My data are the wing area of insects, catched during the 12 years. Each year corresponds to one value of a mean ambient temperature, one value of rainfull and sample of the individuals. My task is the ...
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Homoscedascity tests for Two-Way ANOVA (a factor and a covariate or two factors)

I have the following formula: glm1 <- glm(y ~ g1 + g2, data = fish, family = binomial) y is a binomial variable: num 1 1 0 0 1 0 0 0 0 1 ... #There is (1) or ...
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Correct method of creating a repeated measures ANCOVA in r

I am attempting to build a 3x2 repeated measures ANCOVA in R where the same participants were measured 6 times using 2 different intervention combinations. 6 demographic covariate questions were ...
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ANCOVA with multiple covariates: How to test for homogenity of regression slopes in SPSS

I want to use ANCOVA to test whether means on a dependent variable (DV) differ between 3 groups (the independent variable, IV) while adding 3 variables as covariates (CV). One assumption of ANCOVA is ...
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Is it customary to report a beta coefficient for ANCOVA?

I'm reviewing a paper for a journal, and the authors have reported results of ANCOVA models. They report the F statistic, partial eta squared, beta coefficient, standard error, p value, and R squared. ...
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ANCOVA, Covariates, & Variable Selection

I just want to preface this question by saying: I've searched extensively for answer elsewhere without luck. If, however, you think this question has been answered elsewhere please point me in the ...
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How to test the disturbance effect of a measuring instrument?

I am trying to think of an experimental design that allows me to test to what extent a measuring tool (automatic counting unit) alters (by restricting the entrance area) the measured quantity (number ...
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ANCOVA $\eta^2$ definition

I am struggling to find references to understand what is the exact definition of $\eta^{2}$ is two way anova. Let's say I am estimating the following ANCOVA model: $$ y_{ijk} = \mu + \alpha_i + \...
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What type of ANOVA test should I use?

I have 2 independent categorical variables with 2 groups each, say ind_1 -ind_1a -ind_1b ind2 -ind_2a -ind_2b The outcome variable is quantitative and is measured at ...
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Testing percentages when I may or may not have the original values that give the percentages

I've found tons written about testing proportions between two groups (Fisher's exact test, $\chi^2$-test, logistic regression, etc) but very little on what happens in a t-test-like setting where the ...
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ANCOVA when response variable is calculated from 2 covariates

I have an experiment in which I apply a treatment (g), and measure variables X and Y; the response variable (density; Z) is simply X/Y. If I wanted to know if X or Y, when shifted under the treatment, ...
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Test if intercepts in ancova model are significantly different in R

I ran a model explaining the weight of some plant as a function of time and trying to incorporate the treatment effect. weight ~time + treatment The model looks ...
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MANOVA or repeated measures anova or ANCOVA?

for my thesis I want to compare 3 training groups (2 different types of training and 1 control group) to see the influence on mindfulness-skills and exhaustion level (so 1 IV and 2 DV). All the ...
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Interrupted Time Series Analyses in R with Type-2 Sum Squares ANCOVA Lagged Dependent Variable model

I have a short times series (less than 100 data points). I wonder how to compare effects of intervention I on values of time series. I prepared model on dataset Nile available in R. Let's assume that ...
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AN(C)OVA - Unequal variances even with log transformation

I would like to run an ANCOVA testing the mean difference in # of drinks (DV) consumed by students in 2017 versus students in 2019 (2 groups). Groups are independent and sample sizes are not equal (7,...
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ANOVA: Can a very small Residual Sum of Squares be in part due to a dependent variable of small magnitude?

Substantive Question: Could a very small Residual Sums of Squares be due in large part to a variable of small magnitude? If so, is multiplying the variable by some number (e.g. 10) an appropriate ...
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Equivalence of ANCOVA and repeated measures model

Consider an RCT with individuals i in 2 arms (group, with 0 = control and 1 = treatment) in which one metric outcome (score) is collected at baseline (pre) and after some treatment (post). In an ...
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RMAnova or ANCOVA

I have read many similar questions but I could not find a post completely fit to my experiment design. I have two systems: A system and B system. Participants of Group A use A system to conduct two ...
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ANCOVA: Measured weight of 5 participants 5 times on 3 different weight scales. Should I use participant ID as a covariate?

I measured weight of 5 participants, 5 times each, on 3 different scales accurate to 5 places after decimals. In total, I took: [5 participants] x [5 times each] x [3 different scales] = 75 ...
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The lines on my scatterplot for ANCOVA results doesn't look right, personal error or model error?

I ran an ANCOVA model, to test the effect of treatment on the relationship between two continuous variables (elephant number and plant density) - please see more details in my last question (What ...
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Two way repeated measures with baseline and multiple time-points

We have a repeated measures experiment. Each person had their temperature measured once before, and every minute (for 15 minutes) after two different interventions. As each of the two different ...
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What statistical model can incorporate my categorical variable (2 levels) and 2 continuous variables?

I have some data which has a categorical variable (treatment) with 2 levels, control and 'mice added'. I have 2 continuous variables of plant density and elephant number/density. I have examined the ...
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Research question: We measured heart rate variability parameters

In my research we measured heart rate variability parameters (4 different numerical variables) in 4 different situations in 50 subjects - newborns who were of different age. How to control the sample ...
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Test if post-exposure value is different from pre-exposure value in a follow-up adjusted for baseline analysis using a cumulative probability model?

I'm trying to conduct a follow-up adjusted for baseline analysis using ANCOVA with a proportional odds model (using the rms package in R). After fitting the model I ...
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method for difference score prediction

I am currently working on a longitudinal analysis (with only 2 time measurements, T1 and T2). In this non-randomized data, I have 2 time measurements of fasting glucose as my outcome, i.e. Y1 and Y2 ...
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Continuous Dependent variable, ordinal and continuous as Independent variables

I have a numeric dependent variable, and I'm trying to run a regression model in R using a score (ordinal) and another numeric variable as predictors. Which is the appropiate model (and R code) for ...
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Paired t-test or comparison of difference?

I want to compare anxiety levels of participants before and after an intervention in two groups. Firstly, I intended to use paired t-test, but I realized that there was a confounder that might effect ...
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is the summary() adequate to visualize the intractions among variables in GLMs?

Good afternoon, I'm fitting a GLM with Poisson distribution. Based on the information collected from Zuur et al. (2009) entitled "Mixed Effects Models and Extensions in Ecology with R" I noticed that ...
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continous x categorial interaction with aov-command in R

I've really tried to google it, but so far I couldn't find any information that fully answers my questions, so I'm hoping to get some help here (I'm also happy about links to any resources dealing ...
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Effect size for ANCOVA in R (lm with factor and covariate)

I have data on survival (time in minutes) for animals (salt-marsh hoppers Orchestia gammarellus) from saline and brackish plots, and my model shows a statistically clear interaction between salinity ...
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ANCOVA and moderator variables

I am currently doing research with an independent variable (four treatment groups), a continuous dependent variables, 5 control variables, and 2 continuous moderators. I figured out that I needed to ...
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Dealing with unequal measurements in MLM or ANCOVA

I am tasked with analyzing a preexisting dataset. The experiment is fairly simple, but I'm finding that analyzing the data is challenging due to the fact that the experimental design is not ideal for ...
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Is GEE a good replacement for ANCOVA to analyze change from baseline on 8-points Likert item?

I was asked to analyze adjusted change from baseline. The variable of interest is a customer answer reported on 8-point Likert scale, but constructed from numbers 0 - 8, rather than labels ("weak", "...
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When running an ANCOVA with two time points, how do you include a covariate that only has data at baseline?

I am running an ANCOVA where insufficiently active adults were recruited in self-selected teams (N = 24) to receive a web-based intervention with gamification component (TECH+C) or without (TECH). At ...
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ANCOVA or T tests?

I have data from a pre and post survey taken by adolescents who participated in a 10 month long pen pal exchange. The DV is their attitude toward people from other cultures. Covariates include gender, ...
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Difference between ANCOVA and Randomized Block ANOVA

What is the difference between an ANCOVA and a Randomized Block ANOVA?
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ANCOVA with two (related) factors

I'm analysing data from a repeated-measures study, in two participant groups (call them patient and control groups). I have measured a dependent variable response. Both the patient and control groups ...
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Should I use a GLM or an ANCOVA?

I'm studying leaf litter decay rates of two plant species, as affected by different treatments. As I need to compare the effect of the treatments, my director suggested me the use of an ANCOVA, with ...
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Differences in LSMEANS in R vs SPSS

I am trying to replicate results from SPSS in R. The model is a repeated measure ANCOVA. Funny enough: all the estimated parameter are the same (beta-coefficients, mean differences for contrasts) but ...

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