R代写-STAT6014/STAT6038-Assignment 1
Assignment 1 (Total Marks: 50)
Submit by 5pm on Tuesday 20 Apr 2021
• This assignment is worth 15% of your overall marks for this course and redeemable.
• You must write up your solutions to this assignment by yourself. If you copy someone
else’s work or allow your work to be copied, you will receive a mark of zero for the
assignment and risk very severe academic consequences.
• Your report should be submitted to Turnitin on Wattle as a single pdf document
(less than 50MB) including the following:
1. The assignment cover sheet (available to download from Wattle).
2. Your assignment (no more than 10 pages).
3. An appendix including all the R commands you used (no page limit).
• Assignments should be typed. Your assignment may include some carefully edited
R output (e.g., graphs, tables) and appropriate discussion of these results, as well
as some selected R commands. Please be selective about what you present and only
include as many pages and as much R output as necessary to justify your solution.
Clearly label each part of your assignment and appendix with the question number
and the part of the question that it refers to.
• Unless otherwise advised, use a significance level of 5%.
• Round numeric answers to 4 decimal places (e.g., 0.0012).
• Marks will be deducted if these instructions are not strictly adhered to, especially
when the total report is of an unreasonable length, i.e., more than 10 pages including
graphs and tables. The appendix and the cover sheet are in addition to the above
page limit; but the appendix will generally not be marked, only checked if there is
some question about what you have actually done.
• Name your report “Course code_Uid”, e.g., “STAT2008_u1234567”.
• Try to submit your assignment at least 15 mins before the deadline in case something
unexpected happens, for instance internet issue.
• Late submissions will NOT be accepted. Extensions will usually be granted on
medical or compassionate grounds on production of appropriate evidence, but must
have lecturer’s permission at least 24 hours before the deadline.
Assignment 1 - Sem 1, 2021 Page 1 of 3
Question 1 [13 Marks]
As we know, b0 and b1 are the least squares estimators of the unknown parameters β0
and β1 of simply linear regression model, respectively. In this question, we will study
the correlation between b0 and b1 both from theory and numerical simulations. The
simulation codes are provided as follows:
# Set your Uni ID number as the seed of random number generator.
# For example, if your Uni ID is u1234567, then use
# set.seed(1234567)
x <- 1:10
n <- length(x)
estimates <- matrix(NA, 1000, 2)
names(estimates) <- c("b0","b1")
for(r in 1:1000) {
y <- 1 + 2*x + rnorm(n,0,2)
estimates[r,] <- lm(y~x)$coefficients
(a) [4 marks] Show the covariance of b0 and b1:
Cov(b0, b1) = − X¯
Note that you cannot use the matrix approach introduced in week 6.
(b) [4 marks] Write down the true model and the distribution of the error terms used
in the simulation. Based on this model, calculate the values of the theoretical
covariance and correlation of b0 and b1.
(c) [2 marks] First set your Uni ID number as the seed of random number
generator, e.g., if your Uni ID is u1234567, run set.seed(1234567). Then
run the simulation. Make a scatterplot of b1 against b0 based on the simulation
output. Do these estimates appear to be correlated?
(d) [3 marks] Following part (c), calculate the values of the empirical covariance and
correlation of b0 and b1. Comparing the results with part (b), what do you notice?
Assignment 1 - Sem 1, 2021 Page 2 of 3
Question 2 [37 Marks]
Data file “mammal.csv” (available to download from Wattle) contains the average mass
(Mass) in kg, metabolic rate (Metab) kJ per day and average lifespan (Life) in years
for 95 species for mammals. It has been suggested that metabolic rate is one of the best
single predictor of species lifespan.
(a) [3 marks] Make a scatterplot of Life against Metab and visually check if there are
any high leverage observations. What are the names and species of these mammals?
(b) [2 marks] Make a comment on the relationship between Life and Metab for the
majority of observations. You may need to adjust the x and y coordinates ranges.
(c) [5 marks] Apply natural log transformation to Metab. Then fit a simple linear
regression model by regressing Life on transformed Metab. Provide the fitted
results. Then conduct model diagnostics. Provide the appropriate plots and discuss
your findings regarding model assumptions and unusual observations.
(d) [4 marks] Following the model in part (c), experiment with applying natural log
transformation and square root transformation to the response variable. Select a
best model with the help of scatterplots and sample correlations. Write down the
mathematical form of your selected regression model.
(e) [4 marks] Following your selected model in part (d), fit a simple linear regression
model. Write down the fitted model by mathematical equation. Conduct model
diagnostic, provide the appropriate plots and discuss related results.
(f) [3 marks] Interpret the estimated slope of the fitted model in part (e). Obtain a
95% confidence interval for the slope parameter.
(g) [5 marks] Using ANOVA approach to test whether the model in part (e) is signifi-
cant. You need to write down the hypotheses, provide the ANOVA table. What is
the test statistic, rejection region or p-value, and your conclusion associated with
this test?
(h) [4 marks] With the model in part (e), find a 90% prediction interval for the lifespan
in years of a mammal with the metabolic rate 8000 kJ per day. Interpret this
(i) [7 marks] Kleiber’s law states that on average the metabolic rate of an animal
species is proportional to its mass raised to the power of 3/4. Propose a simple
linear regression model and appropriate hypotheses to check the adequacy of this
theory and explain why. Using this dataset, fit the model and provide the fitted
results. Then test your proposed hypotheses. What’s your conclusion?
Assignment 1 - Sem 1, 2021 Page 3 of 3