A company wants to test clear deck sealants for weather resistance. Three brands of sealants will be testedusing 60 pieces of decking wood. The company wants to create treatment groups of 20 pieces of wood each,and decide to randomize using slips of paper. Select all the approaches that would result in comparabletreatment groups.The numbers 1, 2, and 3 are each written on 20 slips of paper, and the slips areplaced in a hat and shaken well. The top piece of wood from a stack is selected and aslip of paper is drawn from the hat. That piece of wood is assigned to the group numberon the slip. The slip of paper is returned to the hat. This continues until all pieces of woodhave been assigned to a group.The numbers 1, 2, and 3 are written on three slips of paper, put into a hat, and shaken well. Aslip is drawn and the first 20 pieces of wood on the stack are assigned to the group number on theslip. Another slip is drawn and the next 20 pieces of wood are assigned to that group. The remaining
Answer
A
The numbers 1, 2, and 3 are each written on 20 slips of paper, and the slips areplaced in a hat and shaken well. The top piece of wood from a stack is selected and aslip of paper is drawn from the hat. That piece of wood is assigned to the group numberon the slip. The slip of paper is returned to the hat. This continues until all pieces of woodhave been assigned to a group.
B
The numbers 1, 2, and 3 are written on three slips of paper, put into a hat, and shaken well. Aslip is drawn and the first 20 pieces of wood on the stack are assigned to the group number on theslip. Another slip is drawn and the next 20 pieces of wood are assigned to that group. The remainingpieces of wood are assigned to the remaining group.
C
Each piece of decking wood is assigned a number from 1 to 60. The numbers 1–60 are written on slips of paper and placed in a hat and shaken well. Twenty slips are drawn, shakingthe hat after each slip of paper is drawn, and the pieces of wood corresponding to those numbersare placed in group 1. Twenty more slips are drawn in the same way, and the pieces of woodcorresponding to those numbers are placed in group 2. The pieces of wood corresponding to thenumbers on the remaining slips are placed in group 3.
D
The numbers 1, 2, and 3 are each written on 20 slips of paper (20 for each number) and the slips are placed in a hat and shaken well. The top piece of wood from a stack is selected,and a slip of paper is drawn from the hat. That piece of wood is assigned to the group number onthe slip. The slip of paper is not returned to the hat. This continues until all pieces ofwood have been assigned to a group.
Explanation
Comparable groups should be formed by randomly assigning the wood while ensuring each group has 20 pieces. In C, the 60 pieces are randomly divided into three groups of 20. In D, drawing slips without replacement uses exactly 20 slips for each group, so each group also gets 20 randomly selected pieces. A can produce groups of unequal sizes because slips are returned, and B assigns whole consecutive sections of the stack to groups, which may not balance differences among the pieces.
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