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Are any physiological indicators associated with schizophrenia? In a 1990 article, researchers reported the results of a study that controlled for genetic and socioeconomic differences by examining 15 pairs of monozygotic twins, where one of the twins was schizophrenic and the other was not. The researchers used magnetic resonance imaging to measure the volumes (in cm^3) of several regions and subregions of the twins' brains.
1 |
A data frame with 15 observations on the following 2 variables.
volume of left hippocampus of unaffected twin (in cm^3)
volume of left hippocampus of affected twin (in cm^3)
Ramsey, F.L. and Schafer, D.W. (2013). The Statistical Sleuth: A Course in Methods of Data Analysis (3rd ed), Cengage Learning.
Suddath, R.L., Christison, G.W., Torrey, E.F., Casanova, M.F. and Weinberger, D.R. (1990). Anatomical Abnormalities in the Brains of Monozygotic Twins Discordant for Schizophrenia, New England Journal of Medicine 322(12): 789–794.
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 | attach(case0202)
str(case0202)
diff <- Unaffected-Affected
summary(diff)
t.test(diff) # Paired t-test is a one-sample t-test on differences
t.test(Unaffected,Affected,pair=TRUE) # Alternative coding for the same test
boxplot(diff,
ylab="Difference in Hippocampus Volume (cubic cm)",
xlab="15 Sets of Twins, One Affected with Schizophrenia",
main="Hippocampus Difference: Unaffected Twin Minus Affected Twin")
abline(h=0,lty=2) # Draw a dashed (lty=2) horizontal line at 0
## BOXPLOT FOR PRESENTATION:
boxplot(diff,
ylab="Difference in Hippocampus Volume (cubic cm)",
xlab="15 Sets of Twins, One Affected with Schizophrenia",
main="Hippocampus Difference: Unaffected Minus Affected Twin",
col="green", boxlwd=2, medlwd=2, whisklty=1, whisklwd=2,
staplewex=.2, staplelwd=2, outlwd=2, outpch=21, outbg="green",
outcex=1.5)
abline(h=0,lty=2)
detach(case0202)
|
'data.frame': 15 obs. of 2 variables:
$ Unaffected: num 1.94 1.44 1.56 1.58 2.06 1.66 1.75 1.77 1.78 1.92 ...
$ Affected : num 1.27 1.63 1.47 1.39 1.93 1.26 1.71 1.67 1.28 1.85 ...
Min. 1st Qu. Median Mean 3rd Qu. Max.
-0.1900 0.0550 0.1100 0.1987 0.3150 0.6700
One Sample t-test
data: diff
t = 3.2289, df = 14, p-value = 0.006062
alternative hypothesis: true mean is not equal to 0
95 percent confidence interval:
0.0667041 0.3306292
sample estimates:
mean of x
0.1986667
Paired t-test
data: Unaffected and Affected
t = 3.2289, df = 14, p-value = 0.006062
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
0.0667041 0.3306292
sample estimates:
mean of the differences
0.1986667
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