Experimental Design

True or False: In an experiment, the experimental units are simply observed - no treatment is imposed on them

• True

• False

True or False: In an experiment, we can infer a causal (direct cause-and-effect) relationship between two variables.

• True

• False

Athletes who had suffered hamstring injuries were randomly assigned to one of two exercise programs. The first focused on static stretching and the second on agility. The injury recovery time was then analyzed by trainers. Classify this data collection method.

• Sample Survey

• Observational Study - Retrospective Study

• Experiment

• Observational Study - Prospective Study

A group of researchers are analyzing the association between children's school attendance and mental health. One study looked at data of high school seniors attendance records from 6th-11th grade and whether or not they are participating in therapy. Classify this data collection method.

• Sample Survey

• Observational Study - Retrospective Study

• Observational Study - Prospective Study

• Experiment

Does preconditioning improve athletic performance? The students were interested in ischemic preconditioning, which is a technique to create resistance to loss of oxygen through loss of blood supply to tissues. Ischemic preconditioning works by applying brief episodes of restricted blood flow in order to protect against damage from a subsequent longer term episode. In their experiment, they looked at different blood pressure restriction in pounds (10 pounds or 20 pounds) and the length of time the pressure was applied (10 minutes or 20 minutes).

Identify the factors of this experiment. (More than 1 answer)

• 
  -10 pounds vs. 20 pounds

• 
  Length of time pressure was applied

• -10 minutes vs. 20 minutes

• 
  Blood pressure restriction in pounds

Does preconditioning improve athletic performance? The students were interested in ischemic preconditioning, which is a technique to create resistance to loss of oxygen through loss of blood supply to tissues. Ischemic preconditioning works by applying brief episodes of restricted blood flow in order to protect against damage from a subsequent longer term episode. In their experiment, they looked at different blood pressure restriction in pounds (10 pounds or 20 pounds) and the length of time the pressure was applied (10 minutes or 20 minutes).

How many treatments are there for this experiment?

• 0

• 1

• 2

• 4

Researchers at a dog food company want to compare a new lower calorie food with their standard dog food to see if it's effective in helping inactive dogs maintain a healthy weight. They found several dog owners willing to participate in the trial. The dogs have been classified as small, medium, or large breeds, and the company will supply owners with one of the two foods described above. The owners have agreed to not feed their dogs anything else for a period of 6 months, after which the dogs' weights will be checked.

Identify the experimental units of this experiment.

• The dog owners

• The type of food

• The size of dog

• The dogs

To check the effect of hot temperatures on the elasticity of two brands of rubber bands, one box of Brand A and one box of Brand B rubber bands are tested. Ten bands from the Brand A box are placed in a warm car in the sun for two hours and ten bands from the Brand B box are kept at room temperature. The amount of stretch before the breakage is measured on each rubber band, and the mean for the hot bands is compared to the mean for the others. Is this a good experimental design?

• Yes, this is a good experimental design

• No, because more than two brands should be used.

• No, because more temperatures should be used.

• No, because the brand of rubber band is confounded with the explanatory variable (temperature)

In the relationship between the time spent shopping and the number of items bought. The response variable is

• The number of items bought

• The number of items at the shop

• The time spent shopping

• The time spent getting to the shops

What does replication mean in the context of experimental design?

• Repeating the experiment on multiple experimental units

• Randomly assigning treatments to groups

• Using only one treatment per experiment

• Ensuring all experimental units receive the same treatment