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persentation Prof.Dr. Sayneya M.Risk Dean Faculty of Nursing . Learning objectives. After giving this lecture the student should be able to do the following: List the criteria necessary for inferring cause and effect relationships.

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Prof.Dr. Sayneya M.Risk

Dean Faculty of Nursing


Learning objectives

  • After giving this lecture the student should be able to do the following:
  • List the criteria necessary for inferring cause and effect relationships.
  • Distinguish the difference between experimental and quasiexperimental design.
  • Describe the use of experimental design for evaluation research.
  • Critically evaluate the findings of selected studies that test cause and effect relationships.

Purpose of experimental and

quasiexperimental designs:

  • One of the fundamental purposes of scientific research in any profession is to determine cause – and effect relationship.
  • Experimental and quasiexperimental design is used to test nursing interventions, to determine how well they actually work (evaluating the outcomes in terms of efficacy and cost – effectiveness).
difference between experimental and nonexperimental designs
Difference between experimental and nonexperimental designs
  • Experimental design: the researcher actively brings about the desired effect.
  • Non experimental design : the researcher is passively observe behaviors or actions.
  • The findings of experimental and qaiexperimental studies provide the validation of clinical practice and rationale for changing specific aspects of practice.
  • Experimental designs are particularly suitable for testing cause- and effect relationships, because they help to eliminate potential alternative explanations for the findings.
criteria for effective causality
Criteria for effective causality :
  • The causal variable and effect variable must be associated with each other.
  • The cause must precede the effect.
  • The relationship must not be explainable by another variable.
validity of the conclusion
Validity of the conclusion:
  • Means that the experimental treatment, or the (independent variable) caused the desired effect on the outcome or (dependent variable).
  • Validity of the conclusion depends on just how well the researcher has controlled the other variables that may explain the relationship studied.

Remember that: {most researches in nursing is not experimental}


  • Nursing ,(unlike the physical sciences), is still identifying the content and theory of nursing science.
  • An experimental design requires that all of the relevant variables have been defined so that they can be manipulated and studied which is difficult to apply in nursing field.
  • Therefore nonexperimental design used in identifying variables and determining their relationship to each other often, need to be done before experimental studies are performed.
types of experimental and quasiexperimental research designs
Types of experimental and quasiexperimental research designs
  • Experimental designs:
    • True experiment (pretest- posttest control group) design.
    • Solomon four-group design.
    • After-only design
  • Quasiesxperimental designs:
    • Nonequivalent control group.
    • After-only nonequivalent control group design.
    • Time series design.
the true experimental design
The true experimental design

True experimental have three identifying properties

  • Randomization
  • Control
  • Manipulation

These properties allow the other explanations of the phenomenon to be ruled out and thereby provide the strength of the design for testing cause-and effect relationships.

random assignment to groups
Random assignment to groups

Randomization entails two separate processes:

  • Random selection of subjects from the population
  • Random assignment of subjects to treatment and control conditions.

NB: In random assignment to group, each subject has an equal and known probability of being assigned to any group.


Mean introduction of one or more constants into the experimental situation

Control is acquired by:

  • Manipulating the causal or independent variable
  • Randomly assigning subjects to a group.
  • Very carefully prepared experimental protocols
  • Using comparative groups (control groups), or the group that receives the usual treatment, rather than the innovative experimental one.

Means giving the independent variable (such as health education program) to some participants in the study and not to others or by giving different amounts of it to different groups.

Extraneous variables
  • Antecedents variable:

occurs before the study but may affect the dependent variable and confuse the results (such as age, gender, socioeconomic status…..etc).

  • Intervening variable

occurs during the course of the study and is not part of the study, but it affects the dependent variable .An example: (change in health care financing to increase prenatal care for pregnant women) will affect the care provided to these women.

types of experimental designs
Types of experimental designs

Experimental pretest experiment posttest

Random assignment

control group pretest posttest

Some threats cannot be controlled in true experimental design such as (mortality) Researchers can get around this problem in one of two ways:

    • Use different forms of the same test for the two measurement.
    • Use a move complex experimental design called the Solomon four group design

Experimental pretest experiment posttestgroup treatment

control pretest posttest




control experimental posttest

group treatment

control pretest posttest


All four groups have randomly assigned subjects as with experimental studies , but the additional of these last two groups helps to rule out testing threats to internal validity that the before and after groups may experience.

Experimental experiment posttest

group treatment



control posttest


This design is particularly useful when testing effects expected to be a major problem and the number of available subjects is too limited to use a Solomon four group design.
field and laboratory experiments
Field and laboratory experiments

Field and laboratory experiment s share the properties of control, randomization, and manipulation, and they use the same design characteristics but they are conducted in various environments.

  • In the laboratory the researcher has almost total control over the feature of the environment, such as temperature, humidity….etc
  • Field experience are taking place in some real, existing social setting such as hospital or clinic where the phenomenon of interest usually occurs.
advantages and disadvantages of the experimental design
Advantages and disadvantages of the experimental design
  • Advantages:
    • It is the most appropriate for testing cause and effect relationships.
    • It allows nurses to anticipate in a scientific manner the outcomes of their actions and provide the basis for effective high quality care strategies.
    • It is not the one that most commonly used.
    • Experimentations assumes that all of the relevant variables involved in a phenomenon have been identifies and this is not easy in nursing researches.
    • Descriptive studies need to be completed before experimental interventions can be applied.
    • Difficulty in assigning subjects randomly by age or a certain level of income (for example: it is difficult to randomly assigning patients on a hospital floor to different groups when they might talk to each other about the different treatments.
    • It may be disruptive to the usual routine of the field setting where the experiment is done.
    • Just being studied may influence the results of the study (howthrone effect).
quasieperimental designs
Quasieperimental designs

The researcher initiates an experimental treatment, but where some characteristics of a true experiment is lacking

Such as lacking :


or Randomization.

or Manipulation of the independent variable.

type of quasiexperimental designs
Type of quasiexperimental designs

The quasiexperimental design most commonly used in nursing research are:

  • None equivalent control group design.
  • After only nonequivalent control group design
  • Time –series design.
None equivalent control group design looks exactly like the true experiment except that subjects are not randomly assigned to groups.
  • It is commonly used in nursing research studies conducted in field settings.

Experimental pretest experimental posttest

group treatment

control group pretest posttest

what is the problem with the nonequivalent control group design
What is the problem with the NonequIVALENT Control group design?
  • The basic problem with the design is the weakened confidence the researcher can have in assuming that the experimental and comparison groups are similar at the beginning of the study.
  • Threats to internal validity, such as selection maturation, testing, and mortality, are possible with this design.
is the design is strong
Is the design is strong?
  • The design is relatively strong, because the gathering of the data at the time of the pretest allows the researcher to compare the equivalence of the two groups on important antecedent variables before the independent variable is introduced.
b after only nonequivalent control groups
B. After only nonequivalent control groups
  • After only non equivalent control group design is similar to the after- only experimental design, but randomization is not used to assign subjects to group.

Experimental group experiment treatment posttest

control group posttest

This design makes the assumption that the two groups are equivalent and comparable before the introduction of the independent variable.
  • This design is frequently used in nursing research because:
      • There often are limited opportunities for data collection and because it is particularly useful when testing effects may be problematic.
c time series design
C- Time- series design

It is used by researchers when only one group is available, so they study that group over a longer period.


Experimental pretest pretest experiment posttest posttest

Group treatment

control group pretest pretest posttest posttest

It is useful in determining trends.
  • To rule out some alternative explanations for the findings a one- group pretest-posttest design, researchers can measure the phenomenon of interest over a longer period and introduce the experimental treatment sometimes during the course of the data collection period.
  • The use of a time series design would weaken the alternative explanation that the changes occurred because of some thing else that happened during the study period. However, the testing threats to validity looms large in these designs, since measures are repeated so many times.
advantages and disadvantages of quasiexperimental designs
Advantages and disadvantages of quasiexperimental designs


  • Quasiexpermental designs are used frequently because they are practical, feasible and generalizable.
  • These designs are more adaptable to the real- world practice setting than the controlled experimental designs.
  • These designs may be the only way to evaluate the effect of the independent variable of interest.


  • The inability to make clear cause and effect statements.
  • Result of many research done on laboratory animals can not be generalist on human being.
evaluation research and experimentation
Evaluation research and experimentation
  • Such studies are usually associated with quality assurance and evaluation.
  • Studies of evaluation or quality assurance do exactly what the name implies
  • Many early quality assurance studies documented whether nursing care met predetermined standards.
  • Evaluation research is the utilization of scientific research methods and procedures to evaluate a program, treatment, practice, or policy; it uses analytic means to document the worth of an activity
  • Evaluation research uses both experimental and quasiexpermental design (as well as nonexperimental for the purpose of determining the effect or outcomes of a program
Bigman (1961) listed the purposes and uses of evaluation research:
  • To discover whether and how well the objectives are being fulfilled
  • To determine the reasons for specific successes and failures
  • To direct the course of experiment with techniques for increasing effectiveness
  • To uncover principles underlying a successful program
  • To base further research on the reasons for the relative success of alternative techniques
  • To redefine the means to be used for attaining objectives and to redefine sub goals, in light of research finding.
Types of Evaluation researches
  • Formative evaluation research :

Refers to assessment of a program as it is being implemented; usually the focus is on evaluation of the process of a program rather than the outcomes.

  • Summative evaluation research:

Refers to the assessment of the outcomes of a program that is conducted after completion of the program.

The use of experimental and quasiexperemental designs in quality assurance and evaluation studies allows for:
  • The determination not only of whether care is adequate ,but also which method of care is best under certain conditions
  • Such studies can be used to determine whether a particular type of nursing care is cost- effective : that is, that the care not only does what it is intended to do, but also does it at less or equivalent cost.
critiquing criteria
Critiquing criteria
  • What design is used in the study?
  • Is the design experimental or quasiexperimental?
  • Is the problem one of a cause-and-effect relationship?
  • Is the method used appropriate to the problem?
  • Is the design suited to the setting the study?
experimental designs
Experimental Designs:
  • What experimental design is used in the study, and is it appropriate?
  • How are randomization, control, and manipulation applied?
  • Are there any reasons to believe that there are alternative explanations for the findings?
  • Are all threats to validity, including mortality, addressed in the report?
  • Whether the experiment was conducted in the laboratory or clinical setting, are the findings generalizable to the larger population of interest?
quasiexperimental designs
Quasiexperimental Designs:
  • What quasiexperimental design is used in the study, and is it appropriate?
  • What are the most common threats to the validity of the finding of this design?
  • What are the plausible explanations, and have they been addressed?
  • Are the author’s explanations of threats to validity acceptable?
  • What does the author say about the limitations of the study?
  • Are there other limitation related to the design that are not mentioned?
evaluation research
Evaluation Research:
  • Does the study identify a specific problem, practice, policy, or treatment that it will evaluate?
  • Are the outcomes to be evaluated identified?
  • Is the problem analyzed and described?
  • Is the program to be analyzed described and standardized?
  • Is measurement of the degree of change (outcome) that occurs identified?
  • Is there a determination of whether the observed outcome is related to the activity or to some other cause?