Experimental Research in Nursing

  • There are three basic levels of research designs and two sub-levels: (Brink and Wood, 1998)
    • Experimental,
      • experimental and quasi-experimental
    • Survey -
      • comparative and correlational and
    • Exploratory-Descriptive,
      • descriptive and exploratory.
  • Higher levels of design, the degree of control and the level of knowledge about the variables increases.
  • The level of knowledge about pertinent variables should be the greatest at the level of the experiment and is expected to be most limited at the exploratory level.
  • The choice of the appropriate design is based on the current level of knowledge about the research topic.
  • The current level of knowledge and theory about a topic must be thoroughly examined prior to entering into an experimental design.
  • Two methods of examining existing theory on a topic:
    • conceptual mapping of the literature
    • meta analysis of the published literature
  • When a causal relationship between variables can be both predicted and ethically tested, experimental or quasi experimental designs are warranted.
  • Experiments  broadly defined are tests that involve at least one treatment (independent variable), units (subjects) to be analyzed by assignment  or non assignment to a treatment and a comparison for inferring effects that may be attributed to the treatment.
  • Experimental designs must be characterized by three essential elements:
    • randomization,
    • manipulation and
    • control.
  • refers to participants being assigned by chance to either receive or not receive the treatment condition or intervention.
  • A number of procedures exist for assigning individuals to groups such as:
    • coin toss,
    • a random numbers table or
    • computerized random number generators.
  • Each participant has an equal and known probability of being assigned to either the control or the experimental group. 
  • Randomization helps eliminate bias by spreading variability due to extraneous variables equally across the groups under study.
  • The advantage of assigning participants to groups in a random manner is that this should result in the group’s initially being similar to one another prior to the intervention.
  • Random assignment to condition does not guarantee that the two groups will be similar to one another.
  • Based on sampling theory, significant difference(p<0.05) between the two groups will occur in 1:20 cases of assigning participants to groups.
  • The sample size should be large enough or else researcher may wish to consider some additional methods of distributing important variables such as matching or use of more homogeneous population.
  • In some research, it is necessary to randomly assign treatment conditions, to units other than the individual participants.
  • Randomization may be cluster, stratified, fixed or by random assignment.
  • Manipulation is the process of maneuvering the independent variable so that its effect on the dependent variable can be observed.
  • The causative variable must be amenable to manipulation by the investigator.
  • In working to avoid unintended effects researchers should be cautious of the use of reactive measures which can influence participants’ responses to the dependent variable.
  • Even though researcher does not actively manipulate the control group, it is important that he or she be aware of what may be happening to them.
  • Control group should experience all the same things as participants in the experimental group, except the independent variable. 
  • Ethical considerations, organizational policy or some variables like attitudes, age, disease etc which cannot be manipulated may disallow manipulation.
  • The ability of the researcher to manipulate the independent variable is a major source of control in experimental studies.
  • Elimination of threats to valid inference namely the researchers control over the research environment; control over the experimental variable; the ability to identify and rule out threats to internal validity. (Cook and Campbell
  • The last type of control is typically achieved through the use of a comparison or control group and through attention to sources of variance. 
  • The experimental designs in terms of their ability to control variance should consider three kinds of variance:
    • systematic or experimental variance - the effect of IV on the DV
    • extraneous variance - the effects of extraneous variables on the DVs, which is to be controlled by the design, by selecting participants as homogeneous as possible on that variable, matching and using statistical control;
    • error variance - random fluctuations including errors of measurement, which can be controlled by standardizing the instrument/ measurement conditions or using sensitive, reliable instruments.
  • Internal validity is the primary objective of experimental methodology
  • There are of two major types:
    • true experiments and
    • quasi experiments.
  • True experiments include the random assignment of units to comparison groups.
  • Random assignment is an essential component of true experiments.
  • Quasi experiments have a treatment, outcomes and units to be analyzed, but random assignment of units to comparison groups is not included for determining the groups of units to be compared.
  • An important assumption underlying all true experimental designs is that equivalence of groups is maintained throughout the course of the experiment.
  • If experimental and control groups become nonequivalent, the design then becomes quasi experimental.

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