Research Process & Experimental Research Design PDF

RESEARCH PROCESS SELECTING A RESEARCH STRATEGY AND EXPERIMENTAL RESEARCH DESIGN Ms. Uzma Ilyas  Research Process Step 1: Research idea Step 2: Convert research idea into research hypothesis Step 3: Constructs and operational definitions Step 4: Identifying...

RESEARCH PROCESS SELECTING A RESEARCH STRATEGY AND EXPERIMENTAL RESEARCH DESIGN Ms. Uzma Ilyas  Research Process Step 1: Research idea Step 2: Convert research idea into research hypothesis Step 3: Constructs and operational definitions Step 4: Identifying the participants (Sampling) Step 5: Selecting a research strategy Step 6: Selecting a research design Step 7: Conduct the study Step 8: Evaluate the data Step 9: Report the results Step 10: Refine research idea Resear ch design Resear ch strateg y  STEP 5: RESEARCH STRATEGY Definition: A research strategy is a general approach to research determined by the kind of research question that the research study hopes to answer. Types of Research Strategies 1. The Experimental Research Strategy 2. The Quasi-Experimental Research Strategy 3. Non-experimental Research Strategy 4. The Correlational Research Strategy 5. The Descriptive Research Strategy The Experimental Research Strategy Definition: The experimental research strategy establishes the existence of a cause-and effect relationship between two variables. To accomplish this goal, an experiment manipulates one variable while a second variable is measured and other variables are controlled. To rule out the possibility of a coin cidental relationship, an experiment, often called a true experiment, must demonstrate that changes in one variable are directly responsible for causing changes in the second variable.  Four Basic Elements Of Experiment An experimental study contains the following four basic elements: 1. Manipulation. The researcher manipulates one variable by changing its value to create a set of two or more treatment conditions. The primary purpose of manipulation is to allow researchers to determine the direction of a relationship. Suppose, for example, there is a systematic relationship between temperature and ice-cream sales at major-league baseball stadiums, so that temperature and ice- cream sales rise and fall together. 2. Measurement. A second variable is measured for a group of participants to obtain a set of scores in each treatment condition. 3. Comparison. The scores in one treatment condition are compared with the scores in another treatment condition. Consistent differences between treatments provide evidence that the manipulation has caused changes in the scores. 4. Control. All other variables are controlled to be sure that they do not influence the two variables being examined.  A study by Polman et al. (2008) examined the relationship between video game violence and aggressive behavior. In the study, one group of boys was given a violent video game and another group received a nonviolent game. The researchers manipulated the violence of the game by changing from violent to nonviolent. They then measured the behavior of the boys during a free-play period after the video games. Aggressive behavior for boys with the violent game was then compared with behavior for boys with the nonviolent game. During the study, the researchers controlled other variables by ensuring that both groups consisted of 10-year-old boys (same age and same gender) and randomly assigning participant to the different games to ensure that other variables were balanced across the two conditions. The results showed more aggressive behavior after playing a violent game than after playing a nonviolent game PURPOSE OF EXPERIMENTAL RESEARCH STRATEGY The general purpose of the experimental research strategy is to demonstrate the existence of a cause-and-effect relationship between two variables. That is, an experiment attempts to demonstrate that changing one variable (the independent variable) causes changes in a second variable (the dependent variable). This general purpose can be broken down into two specific goals. 1. The first step in demonstrating a cause-and-effect relationship is to demonstrate that the “cause” happens before the “effect” occurs. In the context of an experiment, this means that you must show that a change in the value of the independent variable is followed by a change in the dependent variable. To accomplish this, a researcher first manipulates the independent variable and then observes the dependent variable to see if it also changes. 2. To establish that one specific variable is responsible for changes in another variable, an experiment must rule out the possibility that the changes are caused by an extraneous variable Type of Variables 1. Independent variable 2. Dependent variable 3. Extraneous/confounding variable  Independent variable is the variable manipulated by the researcher. In behavioral research, the independent variable usually consists of two or more treatment conditions to which participants are exposed. The dependent variable is the variable that is observed for changes to assess the effects of manipulating the independent variable. The dependent variable is typically a behavior or a response measured in each treatment condition. Extraneous variables are all variables in the study other than the independent and dependent variables. Or A variable (usually unmonitored) that changes systematically along with the two variables being studied.  Experimental condition: Individuals in the experimental condition do receive the experimental treatment and are often called the experimental group. OR In an experiment, the experimental condition is the condition in which the treatment is administered. Control condition: Individuals in a control condition do not receive the experimental treatment. Instead, OR the control condition is the condition in which the treatment is not administered.  Confoundi Independent Dependent ng/ variable variable extraneou s variable Not Held Manipulate Observed/ Constant/ d Measured Controlled  Example An experimenter wish to study the effects of room temperature on students' performance on an examination. IV= room temperature DV= students’ performance Confounding variable= noise level, amount of light in room, humidity etc.  Class Activity 1. Stephens, Atkins, and 2. Knight and Haslam Kingston (2009) (2010) found that office conducted an experiment workers who had in which participants were designed their office able to tolerate more pain were more productive when they shouted their compared to workers favorite swear words over whose office design was and over than when they shouted neutral words. controlled by an office Identify the manager. For this independent and study, identify the dependent variables independent variable for this study. and the dependent variable. In an experiment examining Ford and Torok (2008) found that the effects Tai Chi on arthritis motivational signs were effective in pain, Callahan (2009) selected increasing physical activity on a a large sample of individuals college campus. Signs such as with doctor-diagnosed arthritis. “Step up to a healthier lifestyle” Half of the participants immediately began a Tai Chi and “An average person burns 10 course and the other half (the calories a minute walking up the control group) waited 8 weeks stairs” were posted by the before beginning the program. elevators and stairs in a college At the end of 8 weeks, the building. Students and faculty individuals who had increased their use of the stairs experienced Tai Chi had less during times that the signs were arthritis pain that those who posted compared to times when had not participated in the there were no signs. course. a. Identify the independent a. Identify the independent and and dependent variable for dependent variables for this this study. study. A researcher is interested in determining whether large doses of vitamin C can help prevent the common cold. The researcher separates the students into two roughly groups. The students in one group are given a daily multivitamin containing a large amount of vitamin C, and the other group gets a placebo (multivitamin with no vitamin C). The researcher then records the number of colds each individual gets during the winter. It was observed that the students who were give multivitamins containing vitamin C reported fewer incidents of cold. Identify the independent and dependent variable in this study? a) Independent variable b) Dependent and variable c) Also suggest ONE extraneous/confounding variable that can affect the result of the study? RESEARCH DESIGN Definition: A research design is a general plan for implementing a research strategy. A research design specifies whether the study will involve groups or individual participants, will make comparisons within a group or between groups, and how many variables will be included in the study.  RESEARCH DESIGN 1.Experimental Research Strategy i. Between-subjects design ii. Within-subjects design 2.Non-experimental Research Strategy i. Non-equivalent Group Designs ii. Pre-post Designs iii.Developmental Research Design Cross-sectional research design Longitudinal research design 3.The Descriptive Research Strategy Observational research designs Survey Research Design Case Study Design Experimental Research Designs Two research designs: 1.Between-subjects design 2.Within-subjects design https://www.youtube.com/watch?v=8GFPZOYZLMg  Between-subjects Design (Independent Group Designs, Comparative Design) Definition: In between subjects design: different people test each condition, so that each person is only exposed to a single treatment. Or A between-subjects experimental design requires a separate, independent group of individuals for each treatment condition. As a result, the data for a between-subjects design contain only one score for each participant. To qualify as an experiment, the design must satisfy all other requirements of the experimental research strategy, such as manipulation of an independent variable and control of extraneous variables. CHARACTERISTICS OF BETWEEN-SUBJECTS DESIGNS The defining characteristic of a between-subjects design is that it compares different groups of individuals. In the context of an experiment, a researcher manipulates the independent variable to create different treatment conditions, and a separate group of participants is assigned to each of the different conditions. The dependent variable is then measured for each individual, and the researcher examines the data, looking for differences between the groups (fig 8.1). The general goal of a between-subjects experiment is to determine whether differences exist between two or more treatment conditions.  For example, one group of individuals is given a list of one- syllable words to memorize and a separate group receives a list of two-syllable words. This type of design, comparing scores from separate groups, is called a between-subjects design. For example, a researcher may want to compare two teaching methods (two treatments) to determine whether one is more effective than the other. In this case, two separate groups of individuals would be used, one for each of the two teaching methods. ASSUMPTIONS OF BETWEEN-SUBJECT DESIGN Random Assignment: Participants should be randomly assigned to different groups to ensure that each group is comparable at the outset. This helps control for confounding variables and reduces selection bias, ensuring that any differences observed are due to the manipulation of the independent variable. Independence of Observations: The responses of participants in one group should not influence the responses of participants in another group. This assumption is crucial for maintaining the integrity of the data and ensuring that each group’s results are independent. Homogeneity of Variance: It is assumed that the variances within each group are approximately equal. This assumption is important for many statistical tests (e.g., ANOVA) used to analyze data from between-subjects designs, as unequal variances can lead to inaccurate conclusions. Normality: The distribution of the dependent variable should be approximately normally distributed within each group, especially when sample sizes are small. This assumption allows for valid statistical inferences. Control of Extraneous Variables: Researchers must account for potential extraneous variables that could affect the outcome. This can include controlling for factors such as participant characteristics (e.g., age, gender) or environmental conditions (e.g., time of day).  BETWEEN SUBJECT DESIGN ADVANTAGES DISADVANTAGES A main advantage of a between-subjects design One disadvantage of between-subjects designs is that is that each individual score is independent they require a relatively large number of participants. from the other scores. Because each participant Remember, each participant contributes only one score is measured only once, the researcher can be to the final data. To compare three different treatment reasonably confident that the resulting conditions with 30 scores in each treatment, the measurement is relatively clean and between-subjects design requires 90 participants. This uncontaminated by other treatment factors. For can be a problem for research involving special populations in which the number of potential participants this reason, a between-subjects experimental is relatively small. For example, a researcher studying design is often called an independent-measures preschool children with a specific learning dis ability experimental design. might have trouble finding a large number of individuals In addition, between-subjects designs can be to participate. used for a wide variety of research questions. The primary disadvantage of a between-subjects design For any experiment comparing two (or more) stems from the fact that each score is obtained from a treatment conditions, it is always possible to unique individual who has personal characteristics that assign different groups to the different are different from all of the other participants. Individual treatments; thus, a between-subjects design is differences are personal characteristics that differ from always an option. one participant to another CONCEPT CHECK 1. Which statement best characterizes a between-subjects experimental design? a. Participants are randomly selected from two different populations. b. Each participant is assigned to one condition of the experiment. c. Each participant is assigned to every condition of the experiment. d. Participants with the same characteristics are assigned to the different conditions of the experiment. 2. Which of the following accurately describes the scores in a between-subjects experiment? e. Only one score is obtained for each participant. f. At least two scores are obtained for each participant. g. One score is obtained for each treatment condition for each participant. h. Each score represents multiple participants.  Within-subjects Design (Repeated Measures, Dependent Groups, Before And After Group Design) A within-subjects experimental design, or repeated-measures experimental design, compares two or more different treatment conditions (or compares a treatment and a control) by observing or measuring the same group of individuals in all of the treatment conditions being compared. Thus, a within-subjects design looks for differences between treatment conditions within the same group of participants. To qualify as an experiment, the design must satisfy all other requirements of the experimental research strategy, such as manipulation of an independent variable and control of extraneous variables. Or Within-subjects (or repeated-measures) study design: the same person tests all the conditions (i.e., all the user interfaces). The defining characteristic of a within-subjects design is that it uses a single group of participants and tests or observes each individual in all of the different treatments being compared. For example, we described an experiment by Stephens, Atkins, and Kingston (2009) examining the effect of swearing on the experience of pain. In the study, participants were asked to place one hand in icy cold water for as long as they could bear the pain. In one condition, the participants were told to repeat their favorite swear word over and over for as long as their hands were in the water. In the second condition, the participants repeated a neutral word. Each participant started in one condition and, after a brief rest, repeated the ice water plunge switching words to the other condition. Thus, all the participants experienced both conditions with a brief rest period in between. The results clearly showed that swearing significantly increased pain tolerance and decreased the perceived level of pain. It also is possible that the different treatment conditions are administered all together in one experimental session.  For example, Schmidt (1994) presented participants with a list containing a mix of humorous and non-humorous sentences, and then asked them to recall as many as possible. The results showed that significantly more humorous sentences were recalled, indicating the humor plays an important role in human memory. In this case, the researcher switched back and forth between the two treatment conditions (humorous and non-humorous) with only a few seconds between one treatment and the next. Whether the treatment conditions are administered in a sequence over time or are presented all together, the key element of a within-subjects design is that all the individuals in one sample participate in all of the treatment conditions. ASSUMPTIONS FOR WITHIN SUBJECT DESIGN Normality: The scores for the dependent variable should be approximately normally distributed within each condition. Sphericity: This assumption refers to the equality of variances of the differences between all combinations of related groups. In simpler terms, it means that the variances among the conditions should be similar. Independence of Observations: While individual scores from the same participant are not independent (since they are measured multiple times), it is assumed that the scores from different participants are independent of each other. Each participant's responses should not influence those of another participant.  WITHIN SUBJECT DESIGN ADVANTAGES DISADVANTAGES The primary advantage of a within-subjects design The primary disadvantage comes from the fact that each is that it essentially eliminates all the problems based on individual differences that are the participant often goes through a series of treatment conditions, primary concern of a between-subjects design. with each treatment administered at a different time. Whenever the treatments occur at different times, there is an opportunity First, a within-subjects design has no individual for time-related factors, such as fatigue or the weather, to differences between groups. There is only one influence the participants’ scores. For example, if a participant’s group of participants, so the group of individuals in performance steadily declines over a series of treatment treatment I is exactly the same as the group of conditions, you cannot determine whether the decline is being individuals in treatment II; hence, there are no caused by the different treatments or is simply an indication that individual differences between groups to confound the participant is getting tired. the study. Another potential problem for a within-subjects design with Second, because each participant appears in every different treatments administered at different times is treatment condition, each individual serves as his participant attrition. In simple terms, some of the individuals who own control or baseline. This makes it possible to start the research study may be gone before the study is measure and remove the variance caused by completed. Because a within-subjects design often requires individual differences. repeated measurements under different conditions for each individual, some participants may be lost between the first measurement and the final measurement. Participants may forget appointments, lose interest, quit, move away, or even die. CONCEPT CHECK 1. A psychologist is studying the effects of sleep deprivation on cognitive performance. She has the same group of participants complete cognitive tests after a normal night’s sleep and again after staying awake for 24 hours. What type of research design is she using? A) Between-subjects design B) Within-subjects design C) Cross-sectional design D) Longitudinal design 2. In a within-subjects design, how many conditions does each participant experience? A) Only one condition B) Two or more conditions C) Only the control condition D) None of the above  COMPARING WITHIN-SUBJECTS AND BETWEEN-SUBJECTS DESIGNS 1. Individual differences. The prospect that individual differences may become confounding variables or increase variance is a major disadvantage of between- subjects designs. However, these problems are eliminated in a within-subjects design. Because the within-subjects design reduces variance, it is generally more likely to detect a treatment effect (if one exists) than is a between-subjects design. If you anticipate large individual differences, it is usually better to use a within-subjects design. 2. Time-related factors and order effects. There is often the potential for factors that change over time to distort the results of within-subjects designs. However, this problem is eliminated in a between-subjects design, in which each individual participates in only one treatment and is measured only once. Thus, whenever you expect one (or more) of the treatment conditions to have a large and long-lasting effect that may influence the participants in future conditions, it is better to use a between-subjects design. 3. Fewer participants. Although it is a relatively minor advantage, we should note once again that a within-subjects design typically requires fewer participants. Because a within-subjects design obtains multiple scores for each individual, it can generate a lot of data from a relatively small set of participants. A between-subjects design, on the other hand, produces only one score for each participant and requires a lot of participants to generate a lot of data. Whenever it is difficult to find or recruit participants, a within-subjects design is a better choice.  CONCEPT CHECK 1. In an experiment to test the effectiveness of two types of exercise programs on weight loss, one group of participants follows Program A, while a separate group follows Program B for eight weeks. After the study, the researchers compare the weight loss results between the two groups. What type of design is being used here? A) Within-subjects design B) Between-subjects design C) Mixed design D) Repeated measures design A psychologist wants to evaluate the impact of two different therapy techniques on anxiety reduction. They have the same group of patients undergo both therapies in a random order and measure their anxiety levels after each therapy session. What type of research design is this? A) Between-subjects design B) Within-subjects design C) Cross-sectional design D) Factorial design A marketing team tests two advertisements by showing one ad to one group of consumers and a different ad to another group. They then measure brand recall after viewing the ads. What type of research design is being utilized? A) Within-subjects design B) Between-subjects design C) Longitudinal study D) Case-control study NONEXPERIMENTAL AND QUASI- EXPERIMENTAL RESEARCH STRATEGIES  NONEXPERIMENTAL AND QUASI- EXPERIMENTAL RESEARCH STRATEGIES The nonexperimental research strategy and the quasi-experimental research strategy typically involve comparison of scores from different groups or different conditions. However, these two strategies use a nonmanipulated variable to define the groups or conditions being compared. The nonmanipulated variable is usually a participant variable (such as college graduate vs. no college) or a time variable (such as before vs. after treatment). The distinction between the two strategies is that nonexperimental designs make little or no attempt to control threats to internal validity, whereas quasi- experimental designs actively attempt to limit threats to internal validity.  Differential Research Design Non-Equivalent Group Posttest-Only Designs PRETEST-POSTTEST QUASI EXP RESEARCH DESIGN ONE-GROUP PRETEST- POSTTEST DESIGN TIME-SERIES & Time-Series Designs INTERRUPTED TIME- SERIES DESIGNS EQUIVALENT TIME- SAMPLES DESIGN CHARACTERISTICS OF QUASI- EXPERIMENTS Lack the degree of control Lack random assignment Researchers seek additional evidence to eliminate threats to internal validity when they do quasi-experiments rather than true experiments. There is a great difference between the power of the true experiment and that of the quasi-experiment. Before facing the problems of interpretation that result from quasi-experimental procedures, the researcher should make every effort possible to approximate the conditions of a true experiment.  THE STRUCTURE OF NONEXPERIMENTAL AND QUASI-EXPERIMENTAL DESIGNS Nonexperimental and quasi-experimental studies often look like experiments in terms of the general structure of the research study. In an experiment, for example, a researcher typically creates treatment conditions by manipulating an independent variable, and then measures participants to obtain a set of scores within each condition. If the scores in one condition are significantly different from the scores in another condition, the researcher can conclude that the two treatment conditions have different effects (Figure 10.1). Similarly, a nonexperimental or quasi-experimental study also produces groups of scores to be compared for significant differences. One variable is used to create the groups or conditions, and then a second variable is measured to obtain a set of scores within each condition. In nonexperimental and quasi- experimental studies, however, the different groups or treatment conditions are not created by manipulating an independent variable. Instead, the groups are usually defined in terms of a specific participant variable (e.g., college graduate/no college) or in terms of time (e.g., before and after treatment). These two methods of defining groups produce two general categories of nonexperimental and quasi- experimental designs: 1. Between-subjects designs, also known as nonequivalent group designs 2. Within-subjects designs, also known as pre–post designs 1. A nonexperimental design; a. makes no attempt to minimize threats to validity. b. makes some attempts to minimize threats to validity. c. controls extraneous variables, similar to an experiment. d. manipulates one variable, similar to an experiment. 2. Which of the following is an example of a nonexperimental study? e. A study comparing self-esteem scores for children with a learning disability versus scores for children without a learning disability f. A study comparing depression scores for one group that is assigned to receive a therapy versus another group that is assigned not to receive a therapy g. A study comparing performance in a room where the walls have been painted yellow versus performance in a room painted blue h. A study comparing cognitive functioning scores for one group of Alzheimer’s patients who are assigned to receive memory therapy versus another group that is assigned not to receive therapy  I. NONEQUIVALENT GROUP DESIGN A nonequivalent group design is a research study in which the different groups of participants are formed under circumstances that do not permit the researcher to control the assignment of individuals to groups, and the groups of participants are, therefore, considered nonequivalent. Specifically, the researcher cannot use random assignment to create groups of participants. A general example of a nonequivalent group design is shown in Figure 10.3. Notice that the groups are differentiated by one specific factor that identifies the groups. In the example evaluating in-class electronic devices, the differentiating factor was the school policy: one high school encouraged use and one banned use. Typically, the purpose of the study is to show that the factor that differentiates the groups is responsible for causing the participants’ scores to differ from one group to the other. For this example, the goal is to show that the school policy concerning electronic devices is responsible for the different levels of student performance in the two schools. Recall that individual differences create a confound whenever the assignment procedure produces groups that have different participant characteristics. For example, the two high schools in the electronic device study may differ in terms of student IQs, socioeconomic background, racial mixture, student motivation, and so on. These variables are all potentially confounding variables because any one of them could explain the differences between the two groups. Because the assignment of participants is not controlled in a study using nonequivalent groups, this type of research always is threatened by individual differences. You may recognize that a non-equivalent groups study is similar to the between-subjects experimental design. However, the experimental design always uses some form of random assignment or matching to ensure equivalent groups. In a nonequivalent groups design, there is no random assignment and there is no assurance of equivalent groups.  In this section, we consider three common examples of nonequivalent group designs: (1)the differential research design, (2) the posttest-only nonequivalent control group design, and (3) the pretest–posttest nonequivalent control group design. The first two designs make no attempt to control or minimize individual differences as a confound and are nonexperimental designs. The third design is a modification of the posttest-only design and is classified as quasi-experimental because it does attempt to minimize the threat of individual differences as a confound.  NONEXPERIMENTAL DESIGNS WITH NONEQUIVALENT GROUPS 1. Differential Research Design A differential research design is a research study that simply compares preexisting groups. A differential study uses a participant characteristic such as gender, race, or personality to automatically assign participants to groups. The researcher does not randomly assign individuals to groups. A dependent variable is then measured for each participant to obtain a set of scores within each group. The goal of the study is to determine whether the scores for one group are consistently different from the scores of another group. Differential research is classified as a nonexperimental research design. 2. Posttest-only Nonequivalent Control Group Design A posttest-only nonequivalent control group design compares two nonequivalent groups of participants. One group is observed (measured) after receiving a treatment, and the other group is measured at the same time but receives no treat ment. This is an example of a nonexperimental research design. This type of study is occasionally called a static group comparison. In this design, one group of participants is given a treatment and then is measured after the treatment (this is the posttest). The scores for the treated group are then compared with the scores from a nonequivalent group that has not received the treatment (i.e., the control group). The neighborhood parks program is a good example of this type of study. The program is administered in one neighborhood, and other neighborhoods that do not receive the parks serve as a nonequivalent control group. Note that the purpose of the study is to show that the parks have an effect by demonstrating a difference in social interactions for the two groups.  A QUASI-EXPERIMENTAL DESIGN WITH NONEQUIVALENT GROUPS 3. Pretest–posttest Nonequivalent Control Group Design A pretest–posttest nonequivalent control group design compares two non equivalent groups. One group is measured twice, once before a treatment is administered and once after. The other group is measured at the same two times but does not receive any treatment. Because this design attempts to limit threats to internal validity, it is classified as quasi- experimental. This type of design also allows a researcher to compare the pretest scores and posttest scores for both groups to help determine whether the treatment or some other, time-related factor is responsible for changes. In the pretest–posttest nonequivalent groups design, however, these time-related threats are minimized because both groups are observed over the same time period and, therefore, should experience the same time- related fac tors. If the participants are similar before treatment but different after treatment, the researcher can be more confident that the treatment has an effect. On the other hand, if both groups show the same degree of change from the pretest to the posttest, the researcher must conclude that some factor other than the treatment is responsible for the change. Thus, the pretest–posttest nonequivalent control group design reduces the threat of individual differences, limits threats from time-related factors, and can provide some evidence to support a cause-and-effect relationship. As a result, this type of research is considered quasi-experimental.  CONCEPT CHECK 1. For which of the following studies does the researcher not control which individuals are assigned to which group? a. Between-subjects experiment b. Within-subjects experiment c. Nonequivalent group design d. Pre–post design 2. Which research design is used by a researcher comparing self-esteem scores for children from divorced families versus scores for children from families with no divorce? e. Differential research design f. Pretest-only nonequivalent control group design g. Pretest–posttest nonequivalent control group design h. Time-series design WITHIN-SUBJECTS NONEXPERIMENTAL AND QUASI-EXPERIMENTAL DESIGNS: PRE–POST DESIGNS Pre–post Design A pre–post design is a research study in which a series of observations is made over time for one group of participants. The goal of the pre–post design is to evaluate the influence of the intervening treatment or event by comparing the observations made before treatment with the observations made after treatment. pre–post design is similar to the pretest–posttest nonequivalent control group design discussed earlier. However, a pre–post design has no control group. In addition, the primary focus of a pretest–posttest nonequivalent control group design is to compare the treatment group and the control group, not to compare the pretest scores with the posttest scores. As a result, the pretest–posttest nonequivalent control group design is primarily a nonequivalent group design, and we have classified it in that category. II. TIME-SERIES DESIGN A time-series design has a series of observations for each participant before a treatment or event and a series of observations after the treatment or event. A treatment is a manipulation administered by the researcher, and an event is an outside occurrence that is not controlled or manipulated by the researcher. Goal of Time-Series Design --- to evaluate the influence of the intervening treatment or event by comparing the observations made before and after the treatment Studies in which series of observations --- made over-time 1. ONE-GROUP PRETEST-POSTTEST DESIGN One-Group Pretest-Posttest Design --- It involves one measurement before treatment & one measurement after treatment for a single group of participants Classified as Non-Experimental Design OXO For Example; a political consultant could evaluate the effectiveness of a new political TV commercial by assessing voters’ attitude toward a candidate before & after they view the commercial Results may demonstrate a change in attitude, however no attempts --- to control threats to internal validity 2. TIME-SERIES AND INTERRUPTED TIME-SERIES DESIGN Time-Series Design --- has a series of observations before a treatment & a series of observations after the treatment An Interrupted Time-Series Design --- consists of a series of observations before an event occurs and after the event occurs Event --- is not a treatment or an experience that is created or manipulated by the researcher OOOXOOO  3. EQUIVALENT TIME-SAMPLES DESIGN Equivalent Time-Samples Design --- consists of a long series of observations during which a treatment is alternatively administered and then withdrawn By repeatedly applying & withdrawing the treatment --- it reduces the likelihood that some coincidental outside event and not the treatment, is responsible for observed changes in behavior O O O X O O O N O O O X O O O N O O O X O O O …. O = Observation, X = Treatment, N = No Treatment (Treatment Withdrawn) Use --- when the treatment effect is temporary  CONCEPT CHECK 1. A clinical psychologist measures body satisfaction for a group of clients diagnosed with anorexia nervosa each day for 1 week before and for 1 week after the psychologist begins a series of group therapy sessions. What kind of design is being used? a. Time-series b. Interrupted time-series c. Equivalent time-samples d. Pretest–posttest design 2. What design is being used by a researcher comparing depression scores before and after treatment in one group of clients? e. Pretest–posttest nonequivalent control group design f. Differential research design g. Pre–post design h. Posttest-only nonequivalent control group design