Description Usage Format Source References Examples

Educational researchers randomly assigned 28 ninth-year students in Australia to receive coordinate geometry training in one of two ways: a conventional way and a modified way. After the training, the students were asked to solve a coordinate geometry problem. The time to complete the problem was recorded, but five students in the “conventional” group did not complete the solution in the five minute alloted time.

1 |

A data frame with 28 observations on the following 3 variables.

- Time
the time (in seconds) that the student worked on the problem

- Treatment
factor variable with two levels—

`"Modified"`

and`"Conventional"`

- Censored
1 if the individual did not complete the problem in 5 minutes, 0 if they did

Ramsey, F.L. and Schafer, D.W. (2013). *The Statistical Sleuth: A
Course in Methods of Data Analysis (3rd ed)*, Cengage Learning.

Sweller, J., Chandler, P., Tierney, P. and Cooper, M. (1990).
Cognitive Load as a Factor in the Structuring of Technical Material,
*Journal of Experimental Psychology General* **119**(2):
176–192.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | ```
str(case0402) # level 1 of Treatment is "Conventional" (1st alphabetically)
attach(case0402)
boxplot(Time ~ Treatment)
median(Time[Treatment=="Conventional"])-median(Time[Treatment=="Modified"])
wilcox.test(Time ~ Treatment, exact=FALSE, correct=TRUE,
alternative="greater") # Rank-sum test; alternative: group 1 is greater
wilcox.test(Time ~ Treatment, exact=FALSE, correct=TRUE,
alternative="two.sided", conf.int=TRUE) # Use 2-sided to get confidence int.
## DOT PLOTS FOR PRESENTATION
xTreatment <- ifelse(Treatment=="Conventional",1,2) # Make numerical values
myPointCode <- ifelse(Censored==0,21,24)
plot(Time ~ jitter(xTreatment,.2), # Jitter the 1's and 2's for visibility
ylab="Completion Time (Sec.)", xlab="Training Method (jittered)",
main="Test Completion Times from Cognitive Load Experiment",
axes=FALSE, pch=myPointCode, bg="green", cex=2, xlim=c(.5,2.5) )
axis(2) # Draw y-axis as usual
axis(1, tick=FALSE, at=c(1,2), # Draw x-axis without ticks
labels=c("Conventional (n=14 Students)","Modified (n=14 Students)") )
legend(1.5,300, legend=c("Did not Complete in 300 sec","Completed in 300 sec."),
pch=c(24,21), pt.cex=2, pt.bg="green")
detach(case0402)
``` |

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