case1102: The Blood-Brain Barrier

Description Usage Format Source See Also Examples

Description

The human brain is protected from bacteria and toxins, which course through the blood–stream, by a single layer of cells called the blood–brain barrier. These data come from an experiment (on rats, which process a similar barrier) to study a method of disrupting the barrier by infusing a solution of concentrated sugars.

Usage

1

Format

A data frame with 34 observations on the following 9 variables.

Brain

Brain tumor count (per gm)

Liver

Liver count (per gm)

Time

Sacrifice time (in hours)

Treatment

Treatment received

Days

Days post inoculation

Sex

Sex of the rat

Weight

Initial weight (in grams)

Loss

Weight loss (in grams)

Tumor

Tumor weight (in 10^(-4) grams)

Source

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

See Also

ex1416, ex1417

Examples

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str(case1102)
attach(case1102)

## EXPLORATION
logRatio <- log(Brain/Liver)
logTime <- log(Time)
myMatrix <- cbind (logRatio, Days, Weight, Loss, Tumor, logTime)
if(require(car)){   # Use the car library
scatterplotMatrix(myMatrix,groups=Treatment,
  smooth=FALSE, diagonal="histogram", col=c("green","blue"), pch=c(16,17), cex=1.5)
}
 
myLm1 <- lm(logRatio ~ Treatment + logTime + Days + Sex + Weight + Loss + Tumor)
plot(myLm1, which=1)          
if(require(car)){   # Use the car library
  crPlots(myLm1) # Draw partial resdual plots. 
}                              

myLm2   <-  lm(logRatio ~ Treatment + factor(Time) + 
  Days + Sex + Weight + Loss + Tumor)  # Include Time as a factor.
anova(myLm1,myLm2)
if(require(car)){   # Use the car library
  crPlots(myLm2) # Draw partial resdual plots. 
}    

summary(myLm2)  # Use backard elimination 
myLm3 <- update(myLm2, ~ . - Days)   
summary(myLm3)  
myLm4 <- update(myLm3, ~ . - Sex)          
summary(myLm4)
myLm5 <- update(myLm4, ~ . - Weight)
summary(myLm5)
myLm6 <- update(myLm5, ~ . - Tumor)
summary(myLm6)                             
myLm7 <- update(myLm6, ~ . - Loss)
summary(myLm7)   # Final model for inference


## INFERENCE AND INTERPRETATION
myTreatment <- factor(Treatment,levels=c("NS","BD")) # Change level ordering 
myLm7a  <- lm(logRatio ~  factor(Time) + myTreatment)
summary(myLm7a) 
beta <- myLm7a$coef
exp(beta[5])         
exp(confint(myLm7a,5))
# Interpetation: The median ratio of brain to liver tumor counts for barrier-
# disrupted rats is estimated to be 2.2 times the median ratio for control rats 
# (95% CI: 1.5 times to 3.2 times as large). 

## DISPLAY FOR PRESENTATION 
ratio <- Brain/Liver
jTime <- exp(jitter(logTime,.2)) # Back-transform a jittered version of logTime
plot(ratio ~ jTime, log="xy",
  xlab="Sacrifice Time (Hours), jittered; Log Scale",
  ylab="Effectiveness: Brain Tumor Count Relative To Liver Tumor Count; Log Scale",
  main="Blood Brain Barrier Disruption Effectiveness in 34 Rats", 
  pch= ifelse(Treatment=="BD",21,24), bg=ifelse(Treatment=="BD","green","orange"),
  lwd=2, cex=2)
dummyTime     <- c(0.5, 3, 24, 72)
controlTerm   <- beta[1] + beta[2]*(dummyTime==3) + 
  beta[3]*(dummyTime==24) + beta[4]*(dummyTime==72)
controlCurve  <- exp(controlTerm)
lines(controlCurve ~ dummyTime, lty=1,lwd=2)
BDTerm        <- controlTerm + beta[5]
BDCurve       <- exp(BDTerm)
lines(BDCurve ~ dummyTime,lty=2,lwd=2)
legend(0.5,10,c("Barrier disruption","Saline control"),pch=c(21,22),
  pt.bg=c("green","orange"),pt.lwd=c(2,2),pt.cex=c(2,2), lty=c(2,1),lwd=c(2,2))

detach(case1102)

Example output

'data.frame':	34 obs. of  9 variables:
 $ Brain    : int  41081 44286 102926 25927 42643 31342 22815 16629 22315 77961 ...
 $ Liver    : int  1456164 1602171 1601936 1776411 1351184 1790863 1633386 1618757 1567602 1060057 ...
 $ Time     : num  0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 3 ...
 $ Treatment: Factor w/ 2 levels "BD","NS": 1 1 1 1 1 2 2 2 2 1 ...
 $ Days     : int  10 10 10 10 10 10 10 10 10 10 ...
 $ Sex      : Factor w/ 2 levels "Female","Male": 1 1 1 1 1 1 1 1 1 1 ...
 $ Weight   : int  239 225 224 184 250 196 200 273 216 267 ...
 $ Loss     : num  5.9 4 -4.9 9.8 6 7.7 0.5 4 2.8 2.6 ...
 $ Tumor    : int  221 246 61 168 164 260 27 308 93 73 ...
Loading required package: car
Loading required package: carData
Warning message:
In applyDefaults(diagonal, defaults = list(method = "adaptiveDensity"),  :
  unnamed diag arguments, will be ignored
Analysis of Variance Table

Model 1: logRatio ~ Treatment + logTime + Days + Sex + Weight + Loss + 
    Tumor
Model 2: logRatio ~ Treatment + factor(Time) + Days + Sex + Weight + Loss + 
    Tumor
  Res.Df    RSS Df Sum of Sq      F  Pr(>F)  
1     26 9.5127                              
2     24 7.1831  2    2.3295 3.8916 0.03437 *
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Call:
lm(formula = logRatio ~ Treatment + factor(Time) + Days + Sex + 
    Weight + Loss + Tumor)

Residuals:
     Min       1Q   Median       3Q      Max 
-1.58034 -0.20482 -0.04134  0.17296  0.96182 

Coefficients:
                Estimate Std. Error t value Pr(>|t|)    
(Intercept)    -4.063527   3.144780  -1.292 0.208609    
TreatmentNS    -0.830930   0.197544  -4.206 0.000312 ***
factor(Time)3   1.089380   0.294004   3.705 0.001106 ** 
factor(Time)24  4.113695   0.337234  12.198 8.90e-12 ***
factor(Time)72  5.136627   0.340967  15.065 9.88e-14 ***
Days            0.019350   0.282007   0.069 0.945864    
SexMale        -0.035751   0.357884  -0.100 0.921257    
Weight          0.001502   0.004740   0.317 0.754079    
Loss           -0.048216   0.027653  -1.744 0.094032 .  
Tumor           0.001379   0.001160   1.189 0.246065    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.5471 on 24 degrees of freedom
Multiple R-squared:  0.9569,	Adjusted R-squared:  0.9408 
F-statistic: 59.26 on 9 and 24 DF,  p-value: 3.287e-14


Call:
lm(formula = logRatio ~ Treatment + factor(Time) + Sex + Weight + 
    Loss + Tumor)

Residuals:
    Min      1Q  Median      3Q     Max 
-1.5888 -0.2022 -0.0435  0.1765  0.9628 

Coefficients:
                Estimate Std. Error t value Pr(>|t|)    
(Intercept)    -3.860768   1.054273  -3.662 0.001174 ** 
TreatmentNS    -0.831894   0.193082  -4.308 0.000224 ***
factor(Time)3   1.083469   0.275448   3.933 0.000588 ***
factor(Time)24  4.123335   0.300412  13.726 3.83e-13 ***
factor(Time)72  5.147192   0.298106  17.266 2.10e-15 ***
SexMale        -0.044372   0.328369  -0.135 0.893593    
Weight          0.001464   0.004612   0.317 0.753601    
Loss           -0.048542   0.026694  -1.818 0.081001 .  
Tumor           0.001384   0.001134   1.221 0.233420    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.5361 on 25 degrees of freedom
Multiple R-squared:  0.9569,	Adjusted R-squared:  0.9431 
F-statistic: 69.43 on 8 and 25 DF,  p-value: 3.786e-15


Call:
lm(formula = logRatio ~ Treatment + factor(Time) + Weight + Loss + 
    Tumor)

Residuals:
     Min       1Q   Median       3Q      Max 
-1.57401 -0.19807 -0.04482  0.16600  0.95240 

Coefficients:
                Estimate Std. Error t value Pr(>|t|)    
(Intercept)    -3.782356   0.863426  -4.381 0.000172 ***
TreatmentNS    -0.831705   0.189397  -4.391 0.000168 ***
factor(Time)3   1.090050   0.265941   4.099 0.000361 ***
factor(Time)24  4.113242   0.285432  14.411 6.56e-14 ***
factor(Time)72  5.135271   0.279327  18.384  < 2e-16 ***
Weight          0.001125   0.003798   0.296 0.769397    
Loss           -0.047682   0.025432  -1.875 0.072077 .  
Tumor           0.001348   0.001079   1.249 0.222958    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.5259 on 26 degrees of freedom
Multiple R-squared:  0.9569,	Adjusted R-squared:  0.9453 
F-statistic: 82.46 on 7 and 26 DF,  p-value: 4.014e-16


Call:
lm(formula = logRatio ~ Treatment + factor(Time) + Loss + Tumor)

Residuals:
     Min       1Q   Median       3Q      Max 
-1.58559 -0.19289 -0.03901  0.19174  0.96590 

Coefficients:
                Estimate Std. Error t value Pr(>|t|)    
(Intercept)    -3.536771   0.237291 -14.905 1.50e-14 ***
TreatmentNS    -0.837443   0.185194  -4.522 0.000110 ***
factor(Time)3   1.114831   0.248141   4.493 0.000119 ***
factor(Time)24  4.146020   0.258631  16.031 2.55e-15 ***
factor(Time)72  5.166075   0.254835  20.272  < 2e-16 ***
Loss           -0.046465   0.024670  -1.883 0.070448 .  
Tumor           0.001365   0.001059   1.289 0.208474    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.5169 on 27 degrees of freedom
Multiple R-squared:  0.9568,	Adjusted R-squared:  0.9471 
F-statistic: 99.55 on 6 and 27 DF,  p-value: < 2.2e-16


Call:
lm(formula = logRatio ~ Treatment + factor(Time) + Loss)

Residuals:
     Min       1Q   Median       3Q      Max 
-1.71130 -0.19563 -0.02871  0.24420  1.22384 

Coefficients:
               Estimate Std. Error t value Pr(>|t|)    
(Intercept)    -3.38562    0.20869 -16.223 9.05e-16 ***
TreatmentNS    -0.77410    0.18064  -4.285 0.000195 ***
factor(Time)3   1.08321    0.24982   4.336 0.000170 ***
factor(Time)24  4.21525    0.25596  16.469 6.18e-16 ***
factor(Time)72  5.20088    0.25637  20.287  < 2e-16 ***
Loss           -0.03252    0.02243  -1.450 0.158206    
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.523 on 28 degrees of freedom
Multiple R-squared:  0.9541,	Adjusted R-squared:  0.9459 
F-statistic: 116.4 on 5 and 28 DF,  p-value: < 2.2e-16


Call:
lm(formula = logRatio ~ Treatment + factor(Time))

Residuals:
     Min       1Q   Median       3Q      Max 
-1.74019 -0.17548 -0.01782  0.24772  1.05512 

Coefficients:
               Estimate Std. Error t value Pr(>|t|)    
(Intercept)     -3.5049     0.1954 -17.937  < 2e-16 ***
TreatmentNS     -0.7968     0.1834  -4.346 0.000155 ***
factor(Time)3    1.1341     0.2520   4.501 0.000101 ***
factor(Time)24   4.2573     0.2591  16.431 3.13e-16 ***
factor(Time)72   5.1539     0.2591  19.892  < 2e-16 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.5328 on 29 degrees of freedom
Multiple R-squared:  0.9506,	Adjusted R-squared:  0.9438 
F-statistic: 139.6 on 4 and 29 DF,  p-value: < 2.2e-16


Call:
lm(formula = logRatio ~ factor(Time) + myTreatment)

Residuals:
     Min       1Q   Median       3Q      Max 
-1.74019 -0.17548 -0.01782  0.24772  1.05512 

Coefficients:
               Estimate Std. Error t value Pr(>|t|)    
(Intercept)     -4.3017     0.2047 -21.010  < 2e-16 ***
factor(Time)3    1.1341     0.2520   4.501 0.000101 ***
factor(Time)24   4.2573     0.2591  16.431 3.13e-16 ***
factor(Time)72   5.1539     0.2591  19.892  < 2e-16 ***
myTreatmentBD    0.7968     0.1834   4.346 0.000155 ***
---
Signif. codes:  0 '***' 0.001 '**' 0.01 '*' 0.05 '.' 0.1 ' ' 1

Residual standard error: 0.5328 on 29 degrees of freedom
Multiple R-squared:  0.9506,	Adjusted R-squared:  0.9438 
F-statistic: 139.6 on 4 and 29 DF,  p-value: < 2.2e-16

myTreatmentBD 
     2.218421 
                 2.5 %   97.5 %
myTreatmentBD 1.524703 3.227771

Sleuth3 documentation built on May 2, 2019, 6:41 a.m.