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Statistical Methods for Engineering and Science Assignment-

Question 1 -

Download the paper which is provided on FLO under Week 8/Assessment/:

More Tweets, More Votes: Social Media as a Quantitative Indicator of Political Behavior Joseph DiGrazia, Karissa McKelvey, Johan Bollen, Fabio Rojas PLOS One, November 2013, Volume 8, Issue 11, page 1-5. and answer the questions below.

This process forms the basis of a critical appraisal and this will assist you in drawing your own conclusions about the study's findings.

Answer each of the questions in your own words. For example, quoting from the abstract that a "cohort study" was carried out is not sufficient.

Statement of objectives

1) What were the investigators' aims and objectives? If they are not stated explicitly in the paper, what do you think they were?

Study design

2) What type of study was carried out? The name of a study type as stated by the investigators (eg randomised controlled trial) is not sufficient, describe in your own words what they did. Do you think the study design is appropriate to the aims and objectives?

Target/reference population

3) What is an appropriate target/reference population for this study? (That is, to whom did the investigators want to generalise the results?)

Source/sampled population

4) Describe the source or sampled population from which sample was drawn. Is this an appropriate choice? Are there any potential biases introduced through specific groups being missed or underpresented?

Sample frame

5) Did the investigators use a sample frame? If so, describe the sample frame and comment on its appropriateness. If not, what would you recommend as a sample frame and why?

Sample selection

6) How was the study sample selected? Is this an appropriate sampling strategy? What, if any, are the potential biases in the sample selection?

Method of measurement

7) What method(s) was (were) used to obtain data from the sample? Comment on the appropriateness of the method(s). Discuss the advantages and disadvantages of other methods that could have been used.

Measurement instrument

8) How were the main variables of interest measured? Were valid and reliable measures obtained? What were the main outcome (dependent) variable(s) and study factors (or exposures or independent variables) of interest?

Statistical analysis

9) Suppose that you were assisting the authors with the data analysis and had to help them with the interpretation of the findings. Describe in your own words the results presented in Table 1 to Table 2.

Authors' conclusions

10) What were the main conclusions drawn by the authors? Are they justified? Based on your reading of the paper, do you agree with them?

Question 2 -

The common fruit fly, Drosophila melanogaster, is the most studied organism in genetic research because it is small, easy to grow and reproduces rapidly. The length of the thorax (where the wings and legs attach) in a population of male fruit flies is approximately Normally distributed with mean 0.900 millimeters (mm) and standard deviation 0.068 mm.

(a) Choose a male fruit fly at random. What is the probability that the fly you choose has a thorax longer than 1mm?

(b) What proportion of male fruit flies have thorax length between 0.8mm and 0.95mm?

(c) What is the length of the thorax in a population of male fruit flies, if only 1% of male fruit flies have this length or longer?

(d) What are lengths of thorax encompass the middle 90% of the normal distribution?

Question 3 -

How did you use your mobile phone?

Adapted from Moore et al (2014) Exercise 8.12.

A Pew Internet poll in 2010 asked mobile phone users about how they used their mobile phones. One question asked whether or not during the past 30 days they had used their phone while in a store to call a friend or family member for advice about a purchase they were considering.

The poll surveyed 1005 adults living in the United States by telephone. Of these, 478 responded that they had used their phone while in a store within the last 30 days to call a friend or family member for advice about a purchase they were considering.

(a) Construct a 90% confidence interval for the proportion of U.S. adult mobile phone users who had used their phone while in a store within the last 30 days to call a friend or family member for advice about a purchase they were considering.

(b) In the previous survey in 2007, a poll reported this same proportion to be 55%. Using the data from this poll in 2010, test the claim that the proportion of U.S. adult mobile phone users who had used their phone while in a store within the last 30 days to call a friend or family member for advice about a purchase they were considering has declined since 2007.

Use all steps for hypothesis testing to make a conclusion at a significance level of 10%.

(c) What assumptions or conditions have you made in statistical inference in parts (a) and (b)? Are they being satisfied?