Stat 250, Section 701, Homework Assignment 3 (Due 6/8/98 in class)

• 1) Please work on the following textbook exercises in Blaisdell (Second edition) [Each 1/2 point = 15 Points in total]:
  • Exercise 4.3, 4.4, 4.6, 4.8, 4.9, 4.12
  • Exercise 4.22, 4.23, 4.24, 4.29, 4.30, 4.41, 4.45
  • Exercise 4.55, 4.56, 4.58, 4.65, 4.66
  • Exercise 4.75, 4.76, 4.81, 4.84, 4.95, 4.97
  • Exercise 4.125, 4.139, 4.140, 4.153, 4.155, 4.156
  
  
• 2) Computer software in any field is highly dependend on the human programmer. Bugs always occurred and will continue to occur in the future. Perhaps one of the most costly bugs was the one a FORTRAN programmer made in the early 60ies by mistyping a ";" instead of a ":" - resulting in the destruction of an expensive space rocket.

  Bugs in statistical software also always occurred. Best known are statistical programs from the 70ies and early 80ies that ended up with negative variances (which is statistically impossible) for particularly small numbers that resulted in internal computer register underflows when these values were squared. Another problem that occurred very frequently was related to random number generators that generated anything else but random numbers - in many cases the numbers repeated themselves in exactly the same order after only a few hundred or thousand values inbetween.

  So - whatever type of software you have - never expect it to be bug-free. Under this point of view, evaluate Webstat at http://www.stat.sc.edu/~west/webstat/version1.0/ and answer the following questions [15 Points in total]:
  
  You may want to work on this particular exercise in groups of 2 or 3 to be most effective.
  
  

  • Test Webstat with some of the data from class. Perhaps the sample of 8 points from the "Payroll/Win" data set we analyzed in much detail in class might be a good example to test WebStat. Make a clear report which features you tested, if the results look numerically OK, and if the graphics are correct (obviously not all of them are since we already have seen that the labeling of histograms seems to be incorrect). Use some other data from class as well.

    Also make notes what kind of a computer you used for your software test, which Web browser you used (Netscape Version x.x, Internet Explorer Version y.y), and what your exact inputs were.

    The intention is to summarize all your comments and send an e-mail that contains your bug reports to those people that develop WebStat. Typically, software developers, in particular at universities, are very thankful for any comment they get on their software!
    
    

  • Move on one step and use the full "Payroll/Win" data set. This data is available in electronic form at http://www.galaxy.gmu.edu/~symanzik/teaching/1998_stat250/victories.dat. Incorporate this data into WebStat (depending on which Web browser/ Java version you use, the ``Data'' -> ``Get Data'' -> ``from URL'' may not work correctly - in that case you can simply copy and paste the data from the given URL into WebStat or even manually type it in). What kind of graphics do you get for the full data set? What is the resulting regression equation? How does this equation based on all 30 points relate to the one based on the 8 sample points only? Do the results appear to be correct?
    
    
  • Based on your experience with this tool, would you recommend it for use for future Stat 250 students (and given that the bugs you found will be removed)? Is WebStat easy to use, does it expect any additional background knowledge that was not taught in class, or did it work straightforward for you? Would you use WebStat again outside class if you have small statistical problems? Which additional features, if any, would you like to see in WebStat?
    
    
  Extra Credit (Due 6/15/98 in class)
  
  Each of the following questions is worth up to 10 points. The policy for extra credit is that final grades will be determined without looking at the extra credit points and cutoff point limits will be set. Only thereafter, extra credits will be added. Therefore, people that feel comfortable that they will be able to achieve the grade they are looking for through regular course work do not have to work on these extra credit questions. However, if you feel uncertain about the outcome of your final grade, you may want to work on one ore multiple of these questions.
  
  
  • 1) In our first homework, we have seen many examples of how to lie with statistical plots by exaggerating dimensions, scales, distances, etc. There exist plenty of these statistically incorrect plots out there in the real world. Look at newspapers, magazines, on the Web, or even your textbooks and see if you can find such plots. If yes, turn in a photocopy (or printout) of this plot, indicate where it has been found, and make precise statements what's wrong with it.
    
    
  • 2) In Quiz 1, we have seen another type of plot (the Weider empire) that occurs very often in the real world - a plot that does provide only very little of the information one would like to have. Can you find similar plots in newspapers, magazines, on the Web, or even your textbooks? If so, then state questions you would like to have answered about the provided data but no such answers have been given in the plot, the accompanying caption or the main text where the plot is coming from. Again, indicate where the plot has been found and turn in a photocopy (or printout) of this plot and the accompanying text.
    
    
  • 3) There must be some reason why your department thinks that Stat 250 is a class you should attend. Write up to 1 page what kind of statistical problems and data you might encounter in your future job. What kind of statistical knowledge do you think would be most useful to help you in this job?
    
    
  • 4) We have seen many small examples where JAVA applets have been used, e.g., to demonstrate the effect of different bin widths for histograms or the ``Let's make a deal'' JAVA applet. The page http://www.stat.sc.edu/~west/javahtml/Histogram.html contains instructions how to modify this example and how to include your own data. Can you create a Webpage that makes use of this particular JAVA applet and gives an introduction to some of our class data set(s) and allows to look at the effect of a varying histogram for this data. It would be ideal if you could create a page that contains two histograms (displaying payroll and wins) as well as the regression applet from http://www.stat.sc.edu/~west/javahtml/Regression.html. As an answer to this question, just provide the URL where your created Web page can be found.
    
    
  Computers
  
  George W. Johnson Center Library (Room 134)
  Mo-Th 7:30am-11pm
  Fr 7:30am-6pm
  Sa 9:00am-6pm
  Sun 12:00noon-11pm
  
  Johnson Center Computer Lab (Room 341 & 343 - enter through 342)
  Mo-Th 8am-10pm
  Fr 8am-8pm
  Sa 9am-8pm
  Sun 9am-10pm
  
  All these rooms contain PCs that support WebStat (this holds for an estimated 100% of the machines) [should I state that I have sampled n=3 machines that all support WebStat ;-].