Question

1. Explain the R code. SAT_2010 <- mutate( SAT_2010, Salary =salary/1000)

Note: column name is case sensitive.

2. For the following R code segment, answer the following questions a) and b)
SAT_plot <-ggplot(data =SAT_2010, aes(x=Salary, y =total)) +
geom_point()+geom_smooth( method ="lm") +
ylab("Average total score on the SAT")+
xlab("Average teacher salary (in thousands")
SAT_plot

a). Explain the code. Specially, pay attention to the ggplot.
b). What will happen if we delete the last line: SAT_plot? Why?

2. What command in the 7.6 creates a variable called SAT_grp, how is the variable's value determined? What sampling technique this is called?

3. What is the cofounding factor in this case, and how does it affect the outcome?

4. Check the running outcome, and see if column Salary is added as a new column, or as a replacement column for salary, explain the reason.

5. In lm (x~y), what is the dependent variable, what is the independent variable?

Answer 1

1. In first question we are creating one extra variable in the SAT_2010 called Salary using already existed variable salary in SAT_2010.
   • to create new variable in the data we are using mutate function from dplyr package.
2. a) ggplot is a function from ggplot2 package.
   • in data parameter we are providing the data frame object, like for which data we have to plot a graph.
   • in aes we have x and y two sub parameters that shows in x we have to give the x-axis variable and in y we have to provide the y-axis variable.
   • geom_point() is useful for create the point symbols for each data point in the graph.
   • geom_smooth("lm") is draw a smooth line using linear model.
   • ylab is useful for creating the y-label for the plot.
   • xlab is useful for creating the x-label for the plot.

b) if you delete last line SAT_plot you will not be able to show the plot you fitted.because you stored the plot object in SAT_plot.

Note: - For 2nd and 3rd questions data and required code not given.

4. Salary added as new column as i mentioned in the 1st question.

• Because there we are using mutate function to create new variable called Salary using already existed variable salary.

5. In lm (x~y), x is dependent variable and y is independent variable.