Question

As part of a study on transportation safety, the U.S. Department of Transportation collected data on the number of fatal accidents per 1000 licenses and the percentage of licensed drivers under the age of 21 in a sample of 42 cities. Data collected over a one-year period follow. These data are contained in the file named “Safety.csv”.

1- Find the sample mean and standard deviation for each variable. Round your answers to the nearest thousandth.

2- Use the function lm() in R to run a simple linear regression model on the data provided. Use the function summary() in R to generate the regression output. Use the function aov() in R to generate the corresponding ANOVA table. You ought to be able to determine which is the dependent variable and which is the independent variable in this SLR model.

Please copy your R code and the result and paste them here.

3- Write down the estimated regression function below and provide a practical interpretation of the coefficient of the independent variable.

4- Please find a 95% confidence interval for the coefficient of the independent variable and provide a practical interpretation of this interval.

5- At the 5% level of significance, is there a significant relationship between the two variables? Why or why not?

6- What is the value of the coefficient of determination for this simple linear regression model? Provide a brief interpretation of this value.

7- Use the information from the ANOVA table to compute the standard error of estimate, a.k,a, residual standard error. This value must match the residual standard error in the regression summary.

8- What is the point estimate of the expected number of fatal accidents per 1000 licenses if there are 10% drivers under age in a city?

9- Suppose we want to develop a 95% confidence interval for the average number of fatal accidents per 1000 licenses for all the cities with 10% of drivers under age 21. What is the estimate of the standard deviation for this confidence interval?

10-Suppose we want to develop a 95% confidence interval for the average number of fatal accidents per 1000 licenses for all the cities with 10% of drivers under age 21. Compute the t value and the margin of error needed for this confidence interval.

Please copy your R code and the result and paste them here.

11-Provide a 95% confidence interval for the average number of fatal accidents per 1000 licenses for all the cities with 10% of drivers under age 21 and a practical interpretation to this confidence interval.

12- Suppose we want to develop a 95% prediction interval for the number of fatal accidents per 1000 licenses for a city with 10% of drivers under age 21. What is the estimate of the standard deviation for this prediction interval?

13- Suppose we want to develop a 95% prediction interval for the number of fatal accidents per 1000 licenses for a city with 10% of drivers under age 21. Compute the margin of error needed for this prediction interval.

14- Provide a 95% prediction interval for the number of fatal accidents per 1000 licenses for a city with 10% of drivers under age 21 and a practical interpretation to this prediction interval.'

PS: I do appreciate your help but please do not simply copy and paste the irrelevant answer

Safety.csv

Percent Under 21	Fatal Accidents per 1000
13	2.962
12	0.708
8	0.885
12	1.652
11	2.091
17	2.627
18	3.83
8	0.368
13	1.142
8	0.645
9	1.028
16	2.801
12	1.405
9	1.433
10	0.039
9	0.338
11	1.849
12	2.246
14	2.855
14	2.352
11	1.294
17	4.1
8	2.19
16	3.623
15	2.623
9	0.835
8	0.82
14	2.89
8	1.267
15	3.224
10	1.014
10	0.493
14	1.443
18	3.614
10	1.926
14	1.643
16	2.943
12	1.913
15	2.814
13	2.634
9	0.926
17	3.256

Answer 1

First import the given dataset "saftey.csv" in to R.

Then run the following R-code.

attach(saftey);
x = saftey$`Percent Under 21`; #independent variable
y = saftey$`Fatal Accidents per 1000`; #dependent variable

Ans (1):

R-code for finding sample means and standard deviations of both variables:

sample_mean_x = mean(x); # sample mean for 'Percent Under 21'
sample_mean_x;
sd_x = sd(x); #standard deviation for 'Percent Under 21'
sd_x;
sample_mean_y = mean(y); # sample mean for 'Fatal Accidents per 1000'
sample_mean_y;
sd_y = sd(y); #standard deviation for 'Fatal Accidents per 1000'
sd_y;

Then the output:

	Percent Under 21 (x)	Fatal Accidents per 1000 (y)
Sample Mean	12	2
Standard Deviation	3.132	1.071

Ans (2):

The R-code for fitting simple linear regression model and ANOVA Table:

model = lm(y~x); #simple linear regression model
summary(model);
anova = aov(model); #corresponding ANOVA table
summary(anova);

Then the output:

#Simple linear regression model:

Call:
lm(formula = y ~ x)

Residuals:

Min	1Q	Median	3Q	Max
-1.2341	-0.2644	0.0077	0.4436	1.4909

Coefficients:

	Estimate	Std. Error	t value	p-value
Intercept	-1.5974	0.3717	-4.298	0.000107 ***
x	0.2871	0.0294	9.767	3.79e-12 ***

---

Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Residual standard error: 0.5894 on 40 degrees of freedom

Multiple R-squared: 0.7046, Adjusted R-squared: 0.6972

F-statistic: 95.4 on 1 and 40 DF, p-value: 3.794e-12

#ANOVA Table:

	df	Sum Sq	Mean Sq	F value	p-value
x	1	33.13	33.13	95.4	3.79e-12 ***
Residuals	40	13.89	0.35

---
Signif. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1

Ans (3):

From the above output, the estimated regression functions is given as,

# Interpretation of coefficient of independent variable:

Recall: In simple or multiple linear regression, the size of the coefficient for each independent variable gives you the size of the effect that variable is having on your dependent variable, and the sign on the coefficient (positive or negative) gives you the direction of the effect. In regression with a single independent variable, the coefficient tells you how much the dependent variable is expected to increase (if the coefficient is positive) or decrease (if the coefficient is negative) when that independent variable increases by one.

In this problem X is "Percent Under 21" and Y is "Fatal Accidents per 1000" so β1^ is our estimate of the number that Fatal Accidents per 1000 increases for every number per 1000 increase in Percent Under 21.

Ans (4):

R-code for finding 95% confidence interval for coeffficient of independent variable:

confint(model, 'x', level = 0.95); #95% confidence interval for coeffficient of independent variable

Then the Output:

# 95% Confidence Interval for coefficient of independent variable:

Lower 95%	Upper 95%
0.227654	0.346452

# Interpretation of confidence interval of independent variable:

We are 95% confidence that it is between 0.2277 and 0.3465 [where by "95%" confidence we mean that if we were to collect new data generated from the same distribution then in 19 out of every 20 experiments we'd get β1^ in this interval].