Quantitative Research Designs 1 Questions for Thought What

Quantitative Research Designs 1

Questions for Thought What is the difference between experimental, quasi-experimental, and nonexperimental? 2

Research Design • Research Design – It is the researcher’s overall plan for • Answering the research question • Testing the research hypotheses 3

Research Design • Research Design – Will involve decisions regarding • Will there be an intervention • What types of comparison will be made • What procedures will be used to control extraneous variables – Extraneous are variables that may affect the independent or dependent variables, and need to be controlled • When and how many times will data be collected from study participants • In what setting will the study occur 4

Types of Quantitative Research Designs 1. Experimental 2. Quasi-experimental 3. Non-experimental 5

Experimental Research Designs • Experimental Designs 6

Experimental Research Designs • Greatest amount of control over the independent variable • Researcher is an active agent rather than a passive observer 7

Experimental Research Designs • Characteristics of Experiments – Manipulation – Control – Randomization • Need to have these three factors to be considered an experimental design 8

Characteristics of Experiments – Manipulation • The researcher does something to study participants • Independent variable is manipulated by administering an experimental treatment or intervention to some participants and withholding it from others or administering another treatment (control group) • The researcher controls and varies the independent variable and observes its effect on dependent variable 9

Characteristics of Experiments – Control • The researcher introduces controls over the experimental situation through use of control groups • Control group is the participants in an experiment that do not receive the experimental treatment and whose performance provides a baseline against which the effects of the treatment can be measured • The researcher compares the control group’s performance on a dependent variable to the experimental group 10

Characteristics of Experiments – Randomization (random assignment) • The researcher assigns study participants to control or experimental groups randomly • Each participant has an equal chance of being included in any group • Each group is considered to be comparable therefore any changes could be attributed to the independent variable (treatment) 11

Experimental Designs • Types: – – – 1. After-only (post-test-only) design 2. Before-after (pretest-posttest) design 3. Factorial Design 4. Repeated-Measures Design 5. Clinical Trials 12

Experimental Designs 1. After-only (post-test-only) design – Two groups – Collection of data after intervention 13

Experimental Designs 2. Before-after (pretest-posttest) design – Collects baseline (pretest data) data before intervention – Then collects data after the intervention (post-test data) 14

Experimental Designs 3. Factorial Design – Manipulation of two or more variables simultaneously – Allows evaluation of main effects (effects resulting from the intervention) and interaction effects (effects resulting from combining the treatment methods) – Participants are assigned at random to a combination of treatments 15

Experimental Designs 4. Repeated Measures Design (crossover design) – Within-subjects designs • A research design in which a single group of subjects is compared under different conditions or at different points in time (i. e. before and after surgery) – The same study participants are used to evaluate more than one treatment/intervention – Participants are randomly assigned – Participants serve as their own control group 16

Experimental Designs 5. Clinical Trials – Involves the testing of a clinical treatment – Random assignment of participants to experimental or control groups – Large sample, can be across the world to increase generalizability – Usually use a before-after or after-only design 17

Advantages/Disadvantages of Experimental Design • Advantages – Most powerful for testing cause and effect hypotheses • Disadvantages – Some variables can not be manipulated – Not feasible – Not ethical – Potential of Hawthorne effect • Being in a study causes people to change their behaviour 18

Advantages/Disadvantages of Experiments • To reduce the potential for the Hawthorne effect – Researchers use double-blind experiments • Neither researcher nor participant know who is getting which treatment 19

Quasi-Experimental Research Designs • Quasi-Experimental Designs 20

Quasi-experimental Research Designs • Involves manipulation of an independent variable • Lacks either randomization or control-group or both *** • Weaker than experimental designs • Uses the term comparison group instead of the term control group • Also known as pre-experimental design 21

Quasi-experimental Research Designs • Types: – 1. Nonequivalent Control-Group Design – 2. Time-Series Design 22

Quasi-experimental Research Designs 1. Nonequivalent Control-Group Before-After Design – Most frequently used quasi-experimental design – Involves a treatment and two or more groups of participants – Collects data before and after intervention – No randomization • Therefore the groups can not be assumed to be equivalent 23

Quasi-experimental Research Designs 2. Time-Series Design – Has neither a control group nor randomization – Involves the collection of data over an extended period of time and the introduction of the intervention during that period – Therefore data is collected before the intervention (multiple collection points) and again after implementation (multiple collection points) 24

Advantages/Disadvantages of Quasi -Experiments • Advantages – Practical • Disadvantages – Cause and effect can not be determined as easily as experimental designs – Could be other reasons for the change in dependent variable (rival hypotheses) 25

Nonexperimental Research Designs • Nonexperimental Designs 26

Nonexperimental Research Designs • Used where the independent variable can not be manipulated • Used when it is unethical to manipulate the independent variable • Useful in descriptive studies 27

Nonexperimental Research Designs • Types: – 1. Ex post facto (correlational) – 2. Descriptive 28

Nonexperimental Research Designs 1. Ex post facto (correlational) – Research is conducted after the independent variable has been manipulated or intervention applied – Studys relationships among variables – No control of independent variable – Can be retrospective or prospective studies 29

Nonexperimental Research Designs – Retrospective • Looks at dependent variable in the present and attempts to link this effect to cause in the past • Looks at present outcomes and tries to determine what factors caused it – Lung cancer currently, linked to smoking in the past – Prospective • Looks at the presumed cause and then goes forward in time to observe presumed effects • Considered stronger than retrospective studies – Smoking currently may cause lung cancer in the future 30

Nonexperimental Research Designs 2. Descriptive Design – Purpose is to observe, describe and document aspects of a situation 31

Advantages/Disadvantages of Nonexperimental Research Designs • Advantages – Good for problems not able to be studied through experimentation • Disadvantages – Can’t determine causal relationships conclusively 32

Research Design and Time • When to use multiple points of data collection – Time-related processes • Phenomena evolves over time • i. e. healing, growth – Time-sequenced phenomena • Sequencing of phenomena – Comparative purposes • Compare phenomena over time – Enhancement of research control 33

Research Design and Time – Cross-sectional Studies • Collection of data at one point in time • Difficult to infer changes and trends over time – Longitudinal Studies • Collect data over an extended period of time • Can show changes over time 34

Research Design and Time – Longitudinal Studies • Trend studies – Different samples from a population are studied over time, always from same population • Panel studies – Same participants supply the data at two or more points in time • Follow up studies – Determine the outcomes of people with a specific condition or who have received a specific treatment 35

Techniques of Research Control • A major purpose of research design is to maximize the researcher’s control over the research situation 36

Techniques of Research Control • Research Control – Concerned with eliminating possible extraneous influences on the dependent variable • A variable that confounds (confuses) the relationship between the independent and dependent variables – Concerned with understanding the true relationship between independent and dependent variables – Research control attempts to exclude contaminating factors, to control the extraneous influences 37

Techniques of Research Control • Controlling External Factors – Want to achieve constancy of conditions • Researcher is confident that situational contaminants or conditions are not affecting the data – Want to control the environment • As environment influences people’s emotions and behaviour – Want to control the time • Maintain constancy of time, control time of day, time of year – Research protocols • Specific procedures are outlined to maintain consistency 38

Techniques of Research Control – Controlling Intrinsic Factors • Intrinsic factors are participant's characteristics – Age, gender, habits 39

Techniques of Research Control – Methods of Controlling Intrinsic Factors • Randomization – Equalized groups in relation to extraneous variables – The best, most effective method • Homogeneity – Only participants who are the same with respect to extraneous variables are included in the study • Matching – Using information about participants’ characterisitcs to form comparison groups • Statistical Control – Statistical analysis 40

Internal and External Validity • Internal Validity – The extent to which it is possible to make an inference that the independent variable is truly influencing the dependent variable – Quasi-experimental, preexperimental and correlational studies are especially susceptible to threats to internal validity – Experimental designs usually reduce threats to internal validity 41

Internal and External Validity • Threats to Internal Validity – – History threat Selection threat Maturation threat Mortality threat 42

Internal and External Validity • Threats to Internal Validity – History threat • Refers to events external to the intervention but occur at the same time which can affect the dependent variable • Threat in quasi-experimental and non-experimental designs • Not usually threat in experimental studies as all groups will be affected by history 43

Internal and External Validity • Threats to Internal Validity – Selection threat (self-selection) • Results from pre-existing differences between groups which may affect the dependent variable • Groups may not be equivalent • Most problematic threat to studies not using experimental design 44

Internal and External Validity • Threats to Internal Validity – Maturation threat • Occurs when changes to the dependent variable (outcome) results from the passage of time 45

Internal and External Validity • Threats to Internal Validity – Mortality threat • Refers to the loss of participants (attrition) from the different groups in the study 46

Internal and External Validity • External Validity – Refers to the generalizability of the research findings to other settings or samples – Does intervention work in another setting or with different people – A good sampling design increases chance of generalizability 47

Reference Loiselle, C. G. , Profetto-Mc. Grath, J. , Polit, D. F. , & Beck, C. T. (2011). Canadian essentials of nursing research (3 rd ed. ). Philadelphia, PA: Lippincott, Williams & Wilkins. 48