BIOL 2300
Name____________________
Introduction to Biostatistics Homework 4
Directions: Write a report of your answers on separate sheets of paper, taking care to prepare a legible and organized report. Put your name on your report. STAPLE ALL PAGES TOGETHER. Answer questions in order and underline or draw a box around any final numerical answers. Show your work for all answers. Full credit will not be given to answers without work, and partial credit may be given when work is shown. Write any written answers or explanations clearly, and be as neat as possible. DUE Thursday, April 24, 2008 1. On-line (http://biol2300.info) you will find data for homework #4. For this problem we have a hypothetical population of 1000 young adults within an age range of 25-35 years. We want to estimate the mean number of white blood cells found in each cubic millimeter of blood for this population. This measurement is often called a WBC. In order to estimate the mean WBC, I want you to randomly sample 30 individuals from our hypothetical population. Here is what you need to do: a. Choose a method that will allow you to select a simple random sample from this population. Your sample must include 30 patients. Keep in mind that each patient has already been assigned a unique ID number ranging from 1 to 1000. In order to get a person’s WBC, simply enter that person’s ID number into the box provided online. Describe in detail the method that you used to select a simple random sample. b. List each sampled patient’s WBC in a table next to their ID number. c. Compute a mean and standard deviation for your sample. These are your estimates for the population mean and standard deviation. d. Calculate the standard error of the mean based on the information computed in part b. e. Determine the degrees of freedom and the t value (from the t table) that you would use to construct 95% confidence interval around an estimate for the population mean. f. Construct 95% confidence interval around an estimate for the population mean and report it in this format: 95% Confidence Interval = y ± t 0.025 ⋅ SE y
g.
Draw a graph showing your estimate for the population mean with error bars representing your 95% confidence interval. The vertical axis should be a measurement of WBC in units of white blood cells per cubic millimeter. The horizontal axis may simply be labeled “Sample Population.”