Reading

Schmidt & Brown (2021). Evidence-Based Practice for Nurses:

• Chapter 8: Quantitative Designs: Using Numbers to Provide Evidence

Objectives

• Explain the three essential components of experimental designs

• Identify major experimental designs

• Discuss the advantages and disadvantages of various experimental designs

• Discuss the key difference between quasi-experimental and experimental designs

• Identify major quasi-experimental designs

• Discuss the advantages and disadvantages of various quasi-experimental designs

• Describe the purpose of nonexperimental designs

• Identify major nonexperimental quantitative designs

• Discuss the advantages and disadvantages of various nonexperimental designs

Experimental Designs

• = Designs involving random assignment to groups and manipulation of the independent variable

• 3 Essential Components of Experimental Designs

  • 1. Randomization

    • Randomization in experimental designs is used in two ways

      • (1) Researchers randomly select participants from the target population

      • (2) Randomly assign participants to groups

  • 2. Control

    • Related to randomization

    • Ways to control for extraneous variables

      • Control group

        • for comparison to the experimental group

      • Exert the highest level of control over the selection of participants, the definitions of the variables, and the environment in which the experiment is conducted

  • 3. Manipulation

    • Manipulate the independent variable for a design to be considered experimental

    • = Administer the intervention

True Experimental Designs

• True Experimental Designs

  • Randomized Controlled Trials (RCTs)

    • = Clinical experimental studies that typically involve large samples and are sometimes conducted at multiple sites

    • 6 characteristics of RCTs

      • (1) They involve a large number of participants, often from diverse geographic areas

      • (2) There are strict guidelines for including participants in a study

      • (3) Participants are randomly assigned to either the intervention or control group

      • (4) Participants in each group must be comparable (equivalent) on either the intervention or control group

      • (5) The intervention is consistently implemented to all participants in the experimental group following a very rigid defined protocol for implementation

      • (6) All participants in both groups are measured on the dependent variable using the same method of measurement at the same points in time

  • 6 types of true experimental designs

    • (1) Two-group pretest-post-test

      • = Participants are randomly assigned to the experimental or control group and are measured before and after the intervention; classic or true experiment

      • Allows researchers to examine within-subjects results as well as between-subjects results

      • Potential disadvantage

        • threats to internal validity

          • introduced from repeated testing

        • mortality

          • Participants are measured more than once and some participants may drop out before the study is completed

    • (2) Two-group posttest-only

      • = Experimental designs where participants are randomly assigned to an experimental or control group and measured after the intervention

      • Used when it is not possible or practical to measure the dependent variable before the intervention is implemented

      • Advantage

        • Because participants are measured once, the followings are minimized:

          • Threats of testing

          • Mortality

      • Disadvantage

        • Threats of selection bias

          • One cannot assume that the two groups are equivalent because there was no measurement at baseline

    • (3) Solomon four-group

      • = An experimental design involving four groups - some receive the intervention, others serve as controls; some are measured before and after the intervention, others are measured only after the intervention

      • Advantage

        • Better than the two-group pretest-posttest design to reduce the threat of testing

        • Better than the two-group posttest-only design to minimize selection bias

      • Disadvantage

        • Sample sizes must be large because there are more groups, meaning

          • Participants must be available

          • Recruitment of participants will take longer

          • Costs will be increase

    • (4) Multiple experimental groups

      • = Experimental designs using two or more experimental groups with one control group

      • Advantage

        • Allows researchers to compare the effects of different interventions on the dependent variable

      • Disadvantage

        • A large number of participants is needed to detect differences across multiple groups

• • • (6) Crossover designs

      • = Experimental designs that use two or more treatments; participants receive treatments in a random order

      • A type of longitudinal design

      • Advantage

        • Smaller sample sizes because only one group of participants is required, and participants serve as their own controls

      • Disadvantage

        • Participants may continue to engage in the first intervention after moving to the second

Quasi-Experimental Designs

• = Research designs involving the manipulation of the independent variable but lacking random assignment to experimental and comparison groups

• 4 types of quasi-experimental designs

  • 1. Nonequivalent control group pretest-posttest

    • = A quasi-experimental design where participants are not randomly assigned to treatment or comparison groups, but are measured before and after an intervention

  • 2. One-group pretest-posttest

    • = A quasi-experimental design where only one group is measured before and after an intervention

  • 3. One-group time series

    • = A quasi-experimental design where one group is measured prior to administering the intervention and then multiple times after the intervention

  • 4. Preexperimental designs

    • = A posttest-only design that involves manipulation of the independent variable but lacks control for extraneous variables

Nonexperimental Designs

• = Research designs that lack manipulation of the independent variable and random assignment

• 3 main purposes

  • (1) describe a phenomenon in detail

  • (2) explain relationships and differences among variables

  • (3) predict relationships and differences among variables

• 2 general categories of nonexperimental designs

  • (1) Correlational designs

    • = Nonexperimental designs used to study relationships between two or more variables

    • Covary

      • = When change in one variable is associated with change in another variable

    • 3 types of correlational designs

      • (I) Descriptive correlational

        • = Correlational design type used to explain the relationships among the variables or groups using a nondirectional hypothesis

      • (II) Predictive correlational

        • = Correlational design where researchers hypothesize which variables are predictors or outcomes

        • Causality cannot be assumed

        • 2 main aims

          • (i) Attempt to determine the amount of variance in an outcome variable that can be explained by multiple predictor variables

          • (ii) Attempt to know how accurately a group of predictor variables can determine group membership

      • (III) Model testing

        • = Correlational design to test a hypothesized theoretical model; causal modeling or path analysis

        • Can only provide a suggestion of causality, not true evidence of causality

  • (2) Descriptive designs

    • = Designs that provide a picture of a situation as it is naturally happening without manipulation of any of the variables

    • Purposes

      • To assess current practice

      • To be used in the early stages of theory development

        • Conceptual and operational definitions of the variables and possible theoretical relationships among the variables can emerge from descriptive studies

    • Variations in names

      • Exploratory designs

        • Nonexperimental design type used when little is known about a phenomenon

      • Comparative designs

        • Descriptive design type that compares two or more groups or variables

      • Survey designs

        • Descriptive design type involving data obtained through participants' self-reports

    • Advantage

      • Flexibility in the methods that can be used to collect data, often leading to more rapid collection of data and cost savings

    • Disadvantage

      • Inability to establish causality