# Biological Data Analysis: Homework 3

## Due Tuesday, October 9

**You must type this and all other homework assignments. Do not e-mail the assignment to me; turn it in early (at 322 Wolf) for a foreseeable absence, or turn it in late after an unexpected absence from class. **

**1.** Look at the balance data set again. Pick one of the measurement variables. For each value of the nominal variable "most disliked class," calculate the mean, standard deviation, standard error, and 95% confidence interval of the measurement variable. (For example, if your measurement variable is shoe size, calculate the mean, standard deviation, etc. of shoe size for all the people who gave "math" as their least favorite class; then calculate mean, etc. for all the people with "chemistry," etc.) Present your results in a nice little table (do NOT just copy from a spreadsheet).

**2.** Use Excel (or another graphing program, if you have one) to draw a bar graph showing the means and standard deviations you calculated in question 1. (The handbook page on graphs gives instructions on how to add error bars in Excel.) Try your best to make it publication-quality, with good informative labels and without unnecessary crap.

**3.** Draw two more graphs like you did for question 2, only one should show means and standard errors, and one should show means and 95% confidence intervals.

**4.** Don't do a statistical test on the data, even if you already know how, but just look at your three graphs. Do you think there is going to be a significant difference between any of the means? What do you see in the data that makes you think that?

**5. **Look at the article you used in homework 1. If it has a graph in it with error bars, look at the figure caption. Do the error bars represent standard error; standard deviation; 95% confidence interval; something else; or does the paper not say what the error bars are? If the paper you used for homework 1 doesn't have a graph with error bars, look at other papers in the same journal until you find one. Just give me the name of the journal and what the error bars you found represent.

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Biological Data Analysis syllabus