Week 3 Assignment

A recent cover story in an issue of Marie Claire For Baby Birds talked about the effects of diet on weight gain amongst chicks. Small animals often feel some anxiety about their appearance. This has spread from birds to rodents, as a cover story in Snff Sqeek (known as the Cavine Cosmo) discussed adolescent guinea pigs' lingering concerns over fitting in, and tooth growth. A small cadre of rodent psychologists fanned out to the middle schools with the message that 'we're all beautiful on the inside.' Nevertheless, there is a growing interest amongst guinea pigs and their parents to explore the effect of Vitamin C on tooth growth and whether dosage or delivery method might have an influence upon efficacy.

data(ToothGrowth);

library("tidyr");
library("stringr");
library("dplyr");
library("knitr");

Fresh! Wicked! The second-to-last letter in the name is a consonant. These are clearly not your parents' R libraries!

We're aware that lunch is in about ten minutes. We will tell you about our main finding, and for the complete substantiation, please refer to the paper.

In Crampton's study, the dose of Vitamin C and the means of delivery were both varied. Exploratory analysis suggested that a higher dose would lead to more tooth growth. We ran a t-test as follows:

t.test(ToothGrowth$len[ToothGrowth$dose==2.0],
ToothGrowth$len[ToothGrowth$dose==0.5],
paired = FALSE, var.equal=FALSE)

    Welch Two Sample t-test

data:  ToothGrowth$len[ToothGrowth$dose == 2] and ToothGrowth$len[ToothGrowth$dose == 0.5]
t = 11.799, df = 36.883, p-value = 4.398e-14
alternative hypothesis: true difference in means is not equal to 0
95 percent confidence interval:
 12.83383 18.15617
sample estimates:
mean of x mean of y 
   26.100    10.605 

The p-value is given in scientific notation because it is so small, and the confidence interval is entirely below zero. The data appears to support with 95% confidence that the 2.0 mg/day group experienced around 2.5 times as much tooth growth as the 0.5 mg/day group.

Crampton, E. W. (1947) The growth of the odontoblast of the incisor teeth as a criterion of vitamin C intake of the guinea pig. The Journal of Nutrition 33(5): 491-504. http://jn.nutrition.org/content/33/5/491.full.pdf

Stay in school, kids*