Hello everyone.
I am working on an Open Stats Lab (https://sites.trinity.edu/osl/) activity
for factorial ANOVA and have posted my analysis on GitHub (link below).
Once I have a significant interaction, how do I conduct a simple-effects
test in R?
The mixed design is unbalanced as follows:
1. within-subjects factor: Time 1, Time 2;
2. between-subjects factor: Condition 1 (ordinary; n = 64), Condition 2
(extraordinary; n = 66).
I imported the data and transformed it into long format.
library(broom)
library(car)
library(nlme)
library(tidyverse)
> zhang_long[, 1:4]
# A tibble: 260 x 4
condition subject_id extra_time extra_rating
<fct> <fct> <fct> <dbl>
1 ordinary 1 t1_extra 1
2 ordinary 2 t1_extra 3
3 ordinary 3 t1_extra 1
4 ordinary 4 t1_extra 1
5 ordinary 5 t1_extra 5
6 ordinary 6 t1_extra 2
7 ordinary 7 t1_extra 2
8 ordinary 8 t1_extra 3
9 ordinary 9 t1_extra 4
10 ordinary 10 t1_extra 6
# ... with 250 more rows
Since this is a practice activity, I can test my analyses against the
published paper. I was able to calculate the appropriate F-value using
car::Anova and nlme::lme.
# Create linear mixed-effects model
extra_lme <- lme(extra_rating ~ condition*extra_time, random
~1|subject_id,
data = zhang_long)
# Print ANOVA summary using type III sum of squares
options(contrasts = c("contr.sum", "contr.poly"))
Anova(extra_lme, type = "III")
But now I am stuck. How do I conduct a simple-effects test for the
interaction between time and condition?
I tried to subset the data by condition.
# Split data by condition
ordinary <- zhang_long %>% filter(condition == "ordinary")
# Simple-effects test
Anova(lme(extra_rating ~ extra_time, random = ~1|subject_id, data ordinary),
type = "III")
This got me very close to the F-value reported in the paper, which is F(1,
128) = **39.86**.
Analysis of Deviance Table (Type III tests)
Response: extra_rating
Chisq Df Pr(>Chisq)
(Intercept) 610.25 1 < 2.2e-16 ***
extra_time 37.81 1 7.797e-10 ***
---
Signif. codes: 0 ?***? 0.001 ?**? 0.01 ?*? 0.05 ?.? 0.1 ? ? 1
What am I doing wrong?
I uploaded a script and Rmarkdown document to GitHub:
https://github.com/corycaaz/osl-zhang-et-al-2014
Any help would be greatly appreciated!
Thank you,
Cory J. Cascalheira
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