#2. There are some confounds in this study that make it difficult to determine whether the changes in the dependent variables were caused by the independent variable (Jackson, 2012; P.229). First, the study does not include a control group, which is the most important element of an experiment. Other confounding factors that could have influenced the result include historical effects due to the duration of the study; Additionally, mortality or attrition rate may be a factor because we knew 50 subjects were selected for the study, but only 29 completed the study (42% attrition rate). It is therefore possible that some of these uncontrolled extraneous variables influenced the research results (Jackson, 2012; P.229).#4. Internal validity refers to the accuracy of research inferences regarding cause and effect, while external validity involves the ability to generalize study findings to other contexts (Cozby & Bates, 2012, p.69). These elements are important because threats to the internal validity of experimental procedures affect the researcher's ability to draw a valid conclusion “from the population data of an experiment” (Creswell, 2014; p. 174). Additionally, the threat to the external validity of the study will influence the ability to generalize the study result "beyond the subjects used for the experiment and beyond the laboratory in which the experiment was conducted (Jackson, 2012; P.239).#6. Both the within-subjects design and the matched-subjects design used different participants in each condition; but a major difference is carryover effects, which mean that participation in one condition change makes participation in the second condition difficult (Jackson, 2012; P.242). What is the purpose of conducting an experiment? How does a...... middle of paper ...... experimental design work in which participants are presented with conditions on a variable that the researcher has deemed relevant to the research. This type of conception shares some commonalities with conceptions between and with subjects. However, in the above mood study, the researcher should strive to match participants (experimental groups/control groups) in the relevant variables (smile; not smile). Since each group includes different people, this will help minimize testing effects and demand characteristics. Since matched subjects experimental designs share the same attributes with between-participant and between-participant design, they have the same advantages of both. But the notable weakness of matched-subject experimental designs is that more subjects will be needed for the research. Additionally, the loss of a subject due to attrition will affect the entire couple (Jackson, 2012; P.242).