Factors That Affect Dependent Variables Were Caused By The Independent Variable?

#2. There are some confounds in this study that make it difficult to adjudge whether the changes in dependent variables were caused by the independent variable (Jackson, 2012; P.229). First, the study has no control group which is the most important elements of an experiment. Other confound that might have influenced the result include history effects due to the length of the study; Also, mortality or attrition rate may be a factor as we knew that 50 subjects were selected for the study but only 29 completed the study (42% attrition rate). So it is possible that some of these uncontrolled extraneous variables influenced the outcome of the research (Jackson, 2012; P.229).
#4. Internal validity refers to the correctness of the research inferences concerning the cause and effect while external validity involves ability to generalize findings of the study to the other settings (Cozby & Bates, 2012, p. 69). These are important because threats to the internal validity of experimental procedures affect the researcher’s ability to make a valid conclusion “from the data about the population in an experiment” (Creswell, 2014; p. 174). Also, threat to external validity of the study will influence the ability to generalize the result of the study “beyond the subjects used for the experiment and beyond the laboratory in which the experiment was conducted” (Jackson, 2012; P.239).
#6. Both within-subjects design and matched-subjects design used different participants in each condition; but one major difference is the carryover effects, that mean participating in one condition changes makes it difficult to participate in the second condition (Jackson, 2012; P.242).
What is the purpose of conducting an experiment? How does an experimental de...

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... design where participants are matched between conditions on variable that the researcher deemed to be relevant to the research. This type of design shares some commonalities with both between-and with-subjects designs. However, on the mood study above, the researcher must endeavor to match participants’ (experimental groups/control groups) in relevant variables (smile; not smile). Because different people are in each group, it will help to minimize testing effects and demand characteristics. Since Matched-Subjects Experimental designs are shares the same attributes with Between-participants design and Within-participants, it has the same advantages of both. But notable weakness Matched-Subjects Experimental designs is that more subjects will be needed for the research. And also, losing one subject due to attrition will affect the entire pair (Jackson, 2012; P.242).