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Internal Validity: a Must in Research Designs

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Internal Validity: a Must in Research Designs Vol. 10(2), pp. 111-118, 23 January, 2015 DOI: 10.5897/ERR2014.1835 Article Number: 01AA00749743 ISSN 1990-3839 Educational Research and Reviews Copyright © 2015 Author(s) retain the copyright of this article http://www.academicjournals.org/ERR Full Length Research Paper Internal validity: A must in research designs Cahit Kaya Department of Psychological Counseling and Guidence, University of Wisconsin- Madison, United State. Received 2 May, 2014; Accepted 31 December, 2014 In experimental research, internal validity refers to what extent researchers can conclude that changes in the dependent variable (that is, outcome) are caused by manipulations to the independent variable. This causal inference permits researchers to meaningfully interpret research results. This article discusses internal validity threats in social and educational research using examples from the contemporary literature, and research designs in terms of their ability to control internal validity threats. An Eric and psychINFO search was performed to the current review of internal validity. The review indicated that appropriate research designs that control possible extraneous variables are needed to be able to meaningfully interpret research results in education and social sciences. Although, pretest- posttest experimental-control group design controls most of the internal validity threats, the most appropriate research design would vary based on the research questions or goals. Key words: Internal validity, education, confounding variables, research design. INTRODUCTION One of the fundamental purposes of educational research concept of conservation at follow-up stage for students is to determine possible relationships between variables. exposed to the popular television exemplars. However, Experimental designs provide the best possible there might be many other factors that can possibly mechanism to determine whether there is a causal influence the learning outcomes of the students. As a relationship between independent and dependent result, the researchers may not have strong confidence in variables by applying an intervention to one group of reporting that the research results were precise. research participants (that is, experimental group) while The extent researchers can conclude that changes in withholding it from another group (that is, control group). the dependent variable (that is, outcome) are caused by Subsequently, performances of the both groups on an manipulations in the independent variable is called outcome variable are compared to determine the possible internal validity. Cook and Campbell (1979) described effect of the intervention (Cook and Rumrill, 2005). internal validity as a phenomenon with which researchers For example, Swiderski and Amadio (2013) examined infer that relationships between independent and the effectiveness of popular television clips as exemplars dependent variables are not random but casual. In other of Piagetian concepts compared to verbal descriptions of words, interval validity of a study is a process to make the same exemplars with a sample of college students. sure changes in the dependent variable are due to the They concluded that an advantage in learning the independent variable, not other confounding variables. E-mail: [email protected]. Authors agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Kaya 112 Internal validity is the sine qua non and conducting participants` and studies` characteristics; changes in experiments with a strong internal validity is, therefore, public policy (for example, changes in public school ideal (Campbell and Stanley, 1966). policies) and weather conditions (for example, improving In order to establish strong internal validity, researchers mood because people are outside more) could also have need to, as much as possible, minimize confounding history effect (Cook and Rumill, 2005). To exemplify variables which are undesirable variables that influence history threat, a student with emotional disturbance might the relationship between independent and dependent start displaying more socially appropriate behaviors after variables (Cook and Rumrill, 2005). Confounding an intervention program, however the student`s variables might vary from one study to another depending appropriate behaviors might not solely be due to the upon experimental conditions. Examples of confounding intervention but also as a result of the students` parents variables include but not limited to changes in the history teaching the student appropriate behaviors during the of participants, familiarity with experimenter and study intervention. conditions etc. One prevailing way to control confounding variables is employing research designs that provide strong internal validity and are compatible with research Maturation conditions (Campbell and Stanley, 1966). Although it is relatively easier to establish internal It refers to processes that changes in respondents` validity in hard sciences, due to the complexity of human actions are simply due to the passage of time (not due to behaviors, it requires much more effort to do that in social a specific event) in addition to the effect of the and educational sciences. Social scientists cannot readily experimental variable. Changes in respondent`s actions claim that treatment is the only cause of change in might be as functions of biological or psychological behavior. In order to have a strong internal validity and changes that occur to participants, including growing provide more accurate results, unlike in hard sciences, older, growing hungrier, growing more tired and the like. social scientists need to override other possible Maturation could be a problem especially in longitudinal explanations of changes in behavior, such as studies where the impact of an intervention is measured developmental variations in participants, and changes in over a long period of time (Onwuegbuize, 2003). To environmental conditions (Cook and Shadish, 1994). exemplify it, a teacher who teaches a class at the end of The study examines internal validity threats observed in the day might not obtain educational improvements as social and educational research illustrated by examples much as other teachers and assume that his/her teaching from contemporary literature. The study also discuss key method is not affective, however, the reason he/she does features of research designs that help to control internal not obtain better educational outcomes might be that the validity threats, and thereby enable researchers to students feel exhausted at the end of the day. interpret research results meaningfully. Testing effect REVIEW It indicates the influence of taking tests one after another. Threats to internal validity It is also called practice effect. With repeated test taking, test takers will obtain better outcomes, not because of Campbell and Stanley (1966) in their classical book of interventions but because they will become more familiar experimental and quasi-experimental designs pointed out with test questions and formats. Although using different eight different classes of extraneous variables. They tests might reduce the possibility of getting higher results, indicated if not controlled, those extraneous variables some improvements might occur anyway due to might have the confounding effect on the dependent participants` increasing familiarity with testing procedure variable. Those threats are explained in the following. (Rogers and Holloway, 1990). For example, if a teacher wants to measure the progress of a student with learning disability and give similar standardized test over and History over, then the student might pick up the correct answer and have high scores as a result of his/her familiarity with History threat refers to any events that happened the tests. between first and second measurement that influence outcome variable in addition to experimental variable. Instrumentation Those events can be anything that affects the results. Although most of those events might closely be related to It refers to having drifts in the calibration of a 113 Educ. Res. Rev. measurement tool, changes in scorers and observers that participants from high achieved schools are more may impact results of the measurements. Instrument motivated to learn than the other school students. effect is most commonly seen when different instruments Experimental mortality are used in pretests and posttests or a measurement tool is administrated by different researchers. In such It refers to the loss of participants in different rates in situations, changes in outcomes might be attributed to experimental and control groups. The loss can be due to inconsistencies in instrumentation (Campbell and death or drop out from studies. A high mortality rate can Stanley, 1966). To exemplify instrumentation threat, cause selection biases if mortality rates are differentiated some teachers tend to give higher scores on exams than within experimental and control groups. Results of other teachers. If an exam is graded by two teachers, the studies will be confounded if mortality has a specific students` results on exams are prone to be influenced by relationships with particular characteristics of either the teachers` tendencies in scoring. experimental or control group participants (Cook and Rumrill, 2005). For example, if a researcher wants to investigate effects of a class intervention on students` Statistical regression academic
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