Answer to Question 1
2
Rationale 1: In this case, the experimental group would have O1' before the X' and O2' after the X,' indicating use of a pretest and a posttest.
Rationale 2: This is an experimental posttest only design. Subjects are randomly assigned to groups (R), the experimental group receives the experimental treatment (X), the comparison group receives the routine treatment (no X), and a posttest is administered to both groups (O1).
Rationale 3: There is no random selection of subjects to the experimental and comparisons groups, so the notation would have no R.'
Rationale 4: In a time series design, there would be additional O' subscript notations, one for each observation.
Answer to Question 2
4
Rationale 1: Pre-experimental designs are those experimental designs that are weak and in which the researcher has little control over the research. This is not the case in this study.
Rationale 2: Quasi-experimental designs are those in which there is either no comparison group or subjects are not randomly assigned to a group. That is not the case in this study.
Rationale 3: The difference between an experimental study and a comparative study lies in the researcher's ability to manipulate the independent variable. In comparative studies, there is no manipulation of the independent variable. That is not the case in this study.
Rationale 4: The study contains all 3 elements of experimental design: 1) manipulation of an independent variable; 2) control/comparison group; 3) random assignment of subjects to groups.
Summary of greenhouse experimental design and results
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