Introduction to Statistical Methods for the Life and Health Sciences

Laboratory 4 - Data Generation and STATA Coding

In previous labs, we have compared several data sets and looked for relation-ships between paired data. In this lab, we will use all our previous commands to reveal the story that the data tell. In place of the step by step directions, you will need to select the commands as you need them. About the Data These data, from a study by Peter Nonacs at the UCLA Department of OBEE, involve the foraging habits of thatch ants and seed harvester ants and the strategies that these ants use to balance their ability to collect food and their exposure to risk. The data were collected at the Sierra Nevada Aquatic Research Laboratory (SNARL) in the Great Basin Desert Province.

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Data description:
Each ant is classified by colony to distinguish ants from the same colony from ants from other colonies. The distance from the mound’s entrance is measured in meters. Each ant’s mass or wtmg measures the amount of food or energy for that ant. Headwidt is the measure of an ant’s head at its widest section and V5 is a scaled measure of headwidth. Worker class or size class sorts the ants by their headwidths. Colony, distance, and sizeclass or worker classes are categorical variables and mass or weight and headwidth are nu-merical variables.

Lab Questions
  1. How large was the sample of thatch ants? 
  2. How many colonies, distances, and size classes were involved? 
  3. Graph and then describe the distribution of masses for the thatch ants in this study. Include the shape, center, and spread of the distribution. Are 1 there any outliers or unusual observations? 
  4. How heavy is a typical thatch ant? 
  5. Graph and the describe the plot for the headwidths of the thatch ants. Include the shape, center, and spread. Are there any outliers or unusual observations? 
  6.  Graph and then describe the relationship between the mass and headwith of the thatch ants. 
  7. Graph and describe the relationship between distance from the mound entrance and mass. 
  8. Compare headwidths to determine if the thatch colonies produce different sized ants? 
  9. Do heavier or larger ants tend to travel farther from the mound in search of food? 
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Ivo D. Dinov, Ph.D., Departments of Statistics and Neurology, UCLA School of Medicine