Informal ANOVA (cont.)

1. Think about 1 potential idea for your MP1. What are your two factors called? What are the levels of those factors?
2. Begin to sketch a parallel dot graph based on hypothetical data you might collect for MP1. What goes on the x-axis? What goes on the y-axis? What about a legend describing the type or colors of your dots?

• Randi's office hours today 3-5p
  • Waiting room system
• Office hour session tonight 7:05-8:20p
  • We'll be doing HW3 problems
  • Answering questions about MP1
• Format for HW3

• Continue design naming activity!
• Level of measurement of response variable
• Six Fisher Assumptions
• Time for discussing MP1 in breakout groups

Randomized Basic Factorial Design BF[1]

The shelf life of meats is the time a prepackaged cut remains salable, safe, and nutritious. Recent studies suggested controlled gas atmospheres as possible alternatives to existing packaging. To test this, beef steaks (75\( g \)) were randomly assigned to packaging with either 1) ambient air in a commercial plastic wrap, 2) vacuum packed, 3) 100% carbon dioxide (\( CO_2 \)), or 4) a mixture of 1% carbon monoxide (CO), 40% oxygen (\( O_2 \)), and 59% nitrogen (N). The number of psychrotrophic bacteria on the meat was measured after nine days of storage at 4 degrees C.

Randomized Basic Factorial Design BF[1]

“Clean” precipitation has a pH in the 5.0 to 5.5 range, but observed precipitation pH in northern New Hampshire is often in the 3.0 to 4.0 range. Is this acid rain hurting trees? 240 six-week-old yellow birch seedlings were randomly assigned to one of 5 groups. Each group received an acid rain mist at the following pH levels: 4.7, 4.0, 3.3, 3.0, and 2.3. After 17 weeks, the seedling were weighed, and their total plant (dry) weight was recorded.

One-Way Complete Block Design CB[1]

Modern zoos try to reproduce natural habitats in their exhibits as much as possible. They try to use appropriate plants, but these plants can be infested with inappropriate insects. Cycads (plants that look vaguely like palms) can be infected with mealybugs, and the zoo wishes to test three treatments: 1) water, 2) horticultural oil, and 3) fungal spores in water. Five infested cycads are taken to to the testing area. Three branches are randomly selected from each tree, and 3 cm by 3 cm patches are marked on each branch. The number of mealybugs on the patch is counted. The three treatments then get randomly assigned to the three branches for each tree. After three days the mealybugs are counted again. The change in number of mealybugs is computed (\( before-after \)).

One-Way Complete Block Design CB[1]

Most people believe that country air is better to breather than city air, but how would you test it? You might start by choosing a response that narrows down what you mean by “better.” One feature of healthy lungs is tracheobronchial clearance—how fast they get rid of nasty stuff. To test this idea, investigators found 7 sets of mono-zygotic twins where one was living in the country and one in the city. Each person inhaled an aerosol of radioactive Teflon particles. Then the level of radioactivity was measured once right after inhaling, and again an hour later. The percent of the original radioactivity remaining was calculated.

Categorical

• nominal: categorical variable whose levels have no ordering.
  • gender, race, etc.
• ordinal: categorical variable whose levels have an order.
  • education level

Numerical

• interval: numerical variable where we assume the distance between points is equal. No true zero.
  • scores on a “self-esteem” scale, measured from 1 to 7
• ratio: numerical variable that has a true zero point.
  • students’ times to complete cognitive task
  • enzyme concentration

• Take turns giving one or two ideas for your MP1. Give each presenter thoughts or suggestions before moving onto the next person.
• Raise your hand if anyone in your group has a question!

• See code 02-Informal ANOVA from the course website