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1 Experimental Research Cause + Effect Manipulation Control.

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Presentation on theme: "1 Experimental Research Cause + Effect Manipulation Control."— Presentation transcript:

1 1 Experimental Research Cause + Effect Manipulation Control

2 2 Cause + Effect Cause(s) = Independent Variable(s) Effect(s) = Dependent Variable(s)

3 3 True Experimental Research Designs Difficult to use in nursing Nonexperimental designs more common

4 4 Internal Validity Are changes in the dependant variable due to effects of the independent variable alone?

5 5 External Validity To what degree can the results of the study be generalized to other people and other settings?

6 6 Extraneous Variables Variables that cannot be controlled May threaten internal and external validity

7 7 Extraneous Variables Confounding Intervening Study Limitations

8 8 Extraneous Variables Threaten internal and external validity Control of one creates problems with others

9 9 Six Threats to Internal Validity Selection Bias History Maturation Testing Instrumentation Change Mortality

10 10 Selection Bias Changes in the dependent variable due to subject differences and not the experimental treatment

11 11 History An event other than the experimental treatment occurs during the course of a study and influences the dependent variable

12 12 Maturation Changes that occur within subjects during an experimental study may influence the study results

13 13 Testing The influence of the pretest or knowledge of baseline data effects the posttest score

14 14 Instrument Change Instrument inaccuracy or judging influences the pretest or posttest scores

15 15 Mortality Attrition or drop out

16 16 Major Threats to External Validity Hawthorne effect Experimenter effect Reactive effects of the pretest

17 17 Hawthorne Effect Study participants respond in a certain manner, not because of the experimental treatment but because they are aware that they are being observed

18 18 Double-blind Experiment Prevents the Hawthorne effect Treatment assignments unknown to researcher and subjects

19 19 Experimenter Effect Occurs in experimental research Researcher characteristics or behaviors influence subject behaviors

20 20 Examples of Influential Researcher Characteristics Facial expressions Clothing Age Gender Type of jewelry Body build

21 21 Rosenthal Effect Occurs in nonexperimental research Interviewer characteristics or behaviors influence respondent’s answers

22 22 Reactive Effects of the Pretest (Measurement Effect) Subjects are sensitized to the experimental treatment through taking the pretest

23 23 Symbolic Presentation of Research Designs Developed by Campbell and Stanley (1963) Used to depict research designs in a symbolic form R = random assignment of subjects to a group O = observation or measurement of dependent variable X = experimental treatment or intervention

24 24 Experimental Research Designs True experimental Quasi-experimental Pre-experimental

25 25 True Experimental Design Internal validity are minimized Causality Researcher has a great deal of control

26 26 True Experimental Design Criteria Researcher manipulates the experimental variable (s) One experimental group and one comparison group Subjects randomly assigned to groups

27 27 Manipulation—First Criteria The independent, or experimental, variable is controlled by the researcher Researcher has control over o the type of experimental treatment that is administered and o who will receive the treatment

28 28 Comparison or Control Group— Second Criteria Group that does not receive the experimental treatment Receive usual treatment or no treatment

29 29 Random Assignment—Third Criteria Each subject has equal chance Decreases Selection Bias

30 30 Experimental Designs Pretest-posttest control group design Posttest-only design Solomon four-group design

31 31 The Pretest-Posttest Control Group Design Subjects randomly assigned to groups Pretest is given to both groups Experimental group receives experimental treatment Comparison group receives routine treatment or no treatment Posttest is given to both groups

32 32 The Pretest-Posttest Control Group Design R O 1 X O 2 R O 1 O 2

33 33 The Pretest-Posttest Control Group Design Advantage Controls for all Internal Validity Threats Disadvantage Causes external threats and Possible reactive effects of the pretest

34 34 The Posttest-Only Control Group Design Subjects randomly assigned to groups Experimental group receives the experimental treatment Comparison group receives routine treatment or no treatment Posttest given to both groups Eliminates reactive effects of pretest

35 35 The Posttest-Only Control Group Design R X O 1 (Experimental group) R O 1 (Comparison group) Eliminates the reactive effects of the pretest on the posttest

36 36 The Solomon Four-Group Design R O 1 X O 2 (Experimental Group 1) R O 1 O 2 (Comparison Group 1) R X O 2 (Experimental Group 2) R O 2 (Comparison Group 2)

37 37 Solomon Four-Group Design Advantages Minimizes threats to both internal and external validity Differences between groups can be associated with the experimental treatment Disadvantages Requires large sample Statistical analysis is complicated

38 38 Quasi-Experimental Designs No comparison group No randomization Nonequivalent Control Group Design Time-series Design

39 39 Quasi-Experimental Designs Advantages Convenient Approximates the real world Disadvantages Decreases researcher control Decreases researcher manipulation

40 40 The Nonequivalent Control Group Design Similar to pretest-posttest control group design No random assignment of subjects to groups

41 41 The Nonequivalent Control Group Design O 1 X O 2 (Experimental Group) O 1 O 2 (Comparison Group)

42 42 The Nonequivalent Control Group Design Biggest threat to internal validity Selection bias

43 43 Time-Series Design Researcher observes or measures the subjects Experimental treatment administered between two of the observations O 1 O 2 O 3 X O 4 O 5 O 6

44 44 Time-Series Design Threats to Internal Validity History Testing

45 45 Learning Objective 8 Discuss two pre-experimental designs

46 46 Pre-Experimental Designs One-shot Case Study One-group Pretest-Posttest Design

47 47 The One-Shot Case Study X O Controls for no threats to Internal Validity Weak design

48 48 The One-Group Preset-Posttest Design O 1 X O 2 Threats to Internal Validity History Maturation Instrumentation Change

49 49 Learning Objective 9 Discuss four types of nonexperimental designs

50 50 Nonexperimental Research Descriptive No manipulation No control of variables

51 51 Nonexperimental Research Survey Research Correlational Research Comparative Research Methodological Research

52 52 Survey Research Self-report data Phone, mail, or through personal contact

53 53 Survey Research Data collection methods Questionnaires Interviews

54 54 Strengths of Survey Research Provide accurate information on populations Use relatively small samples Collect large amounts of data quickly Minimal cost

55 55 Weaknesses of Survey Research Self-report data may be unreliable Subjects tend to provide socially acceptable responses

56 56 Correlational Research Explores the relationship between two or more variables One variable is X. The other variable is Y

57 57 Correlational Coefficient Indicates the strength and direction of relationships Indicates positive (+) or negative (-) information Perfect positive correlation: +1.00 Perfect negative correlation: -1.00 No correlation/relationship: 0.00 Reported through Pearson’s product-moment correlation (Pearson r)

58 58 Correlational Research No manipulation of a variable Possible to identify an independent and dependent variables

59 59 Correlational Research The independent variable Usually comes first in chronological order Influences the dependent variable

60 60 Correlational Research Purpose is to explain relationships between variables Cannot establish cause and effect Useful for generating hypotheses Guides future experimental and quasi- experimental studies

61 61 Comparative Research Examines differences between groups on dependent variable No manipulation of the independent variable Independent variable is often a characteristic of the subjects Independent variable cannot ethically be manipulated

62 62 Comparative Studies Retrospective Ex post facto Prospective

63 63 Retrospective Comparative Study Dependent variable (effect) is identified in the present Researcher tries to determine the independent variable (cause) that preceded it Cannot use an experimental approach for the study

64 64 Prospective Studies Independent variable (presumed cause) is identified in the present Subjects are followed into the future in order to observe the possible occurrence of the dependent variable (effect) May use an experimental approach

65 65 Methodological Studies Research Instruments and Methods Development Testing Evaluation

66 66 Secondary Analysis Studies Analyses data gathered in a previous study May test new hypotheses May ask new questions of the data Cost-effective Efficient

67 67 Learning Objective 10 Describe two types of settings in which research is conducted

68 68 Research Settings Laboratory Studies Field Studies

69 69 Laboratory Studies Conducted in specially created environments Research environment controlled by researcher

70 70 Simulation Studies Laboratory studies Subjects’ responses to descriptions of case studies measured Real-life situations represented in studies

71 71 Field Studies Real-life setting “In the field” Very little control maintained by the researcher Phenomena studied in the natural environment Very appropriate for nursing research

72 72 Learning Objective 11 Critique the design section of quantitative studies

73 73 Critique of Quantitative Research Designs Read the entire research report carefully Determine if the appropriate design is used

74 74 Questions for the Critique Does it test the hypothesis(es)? Does the design answer the research question(s)? Is the researcher trying to determine cause- and-effect? Is the researcher trying to describe a phenomenon from the research subject’s point of view?

75 75 Critiquing the Quantitative Research Design Is the design clearly identified in the research report? Is the design appropriate to test the study hypothesis(es) or answer the research question(s)? If the study used an experimental design, was the most appropriate type of experimental design used? If the study used an experimental design, what means were used to control for threats to internal validity? External validity?

76 76 Critiquing the Quantitative Research Design Does the research design allow the researcher to draw a cause-and-effect relationship between the variables? If the design was nonexperimental, would an experimental design have been more appropriate? What means were used to control for extraneous variables, such as subject characteristics, if a nonexperimental design was used?

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