Consider an experiment that was conducted to study the effects of three types of
ID: 3053289 • Letter: C
Question
Consider an experiment that was conducted to study the effects of three types of feed (A, B, and C) on gene expression in pigs. A total of 36 pigs were housed in 12 pens with 3 pigs in each pen. The 3 feed types were randomly assigned to the 12 pens with 4 pens for each feed type. After three weeks, 36 Affymetrix GeneChips were used to measure gene expression in muscle issues from the 36 pigs. One GeneChip was used for each pig. a. Name the treatments in this experiment. b. Name the experimental units in this experiment. c. Name the observational units in this experiment. d. Name the response variable or variables in this experiment. 20
Explanation / Answer
Answer: a) Each of three feed types A, B and C represents treatments
b) The feed types were randomly assigned to the pens, so the pens are the experimental units. A pen consisting of 3 hogs is one experimental unit
c) Gene expression in muscles was measured separately for each pig, so the pigs are the observational units. More specifically we could say that a muscle sample from a single pig is a single observational unit.
d) Each probe set on the GeneChip corresponds to a response variable. Thus we will have several thousand response variables in this example.