Chapter 12 Quantitative Questions and Procedures

Quantitative Research Uses measurement to determine the effectiveness of interventions Involves measuring objective characteristics that are reported as numbers

Quantitative Research Question PICO Population of Interest Intervention under study Comparison that makes up control Outcome/s of Interest

Characteristics of Quantitative Research Designs Provide a high level of control Allow measurement of probability of error Enable the nurse to: –Appraise the effectiveness of interventions –Determine the relationship between actions and outcomes –Measure changes over time

Common Elements An interest in variables Control over the experiment Use of measurement to compare groups Statistical data analysis A priori design – established prior to the study

Common Designs used in Nursing Research Experimental designs Quasi-experimental designs Studies of intact groups –Ex Post Facto –Causal-comparative –Case/control Time series designs

Experimental Designs The only design that allows for conclusion of cause and effect Random assignment of subjects to groups Manipulated independent variable Measurement of an outcome of interest High levels of internal control Must include randomization, an intervention, & a control group

Quasi-Experimental Design Very similar to experimental design Missing either randomization or a control group Primary distinction: assignment to groups is not random Evidence of cause and effect is not as strong a result

Studies of Intact Groups Ex Post Facto Causal-Comparative Case/Control All of these designs involve: –Finding subjects with a characteristic of interest –Matching them to a comparison group without the characteristic –Measuring an outcome of interest

Ex Post Facto Design Intact group design Relies on observation of relationships between naturally occurring differences in the intervention & outcomes Data is collected after the fact (retrospective) Weakens capacity for reliable and valid data to show cause & effect

Causal-Comparative Design Intact group design Categorization of subjects into groups An outcome of interest is measured Differences are attributed to differences in the classification or category of the group (ie. gender, ethnicity)

Case-control Study Intact group design Observation of subjects who exhibit a characteristic matched with subjects who do not have the characteristic Differences between the subjects allows study of the relationship between the risk & disease Do not have to expose subjects to the risk Always look backward in time (retrospective)

Characteristics of Intact Group Designs Population of interest is identified Group characteristics are identified Outcome of interest is defined Variables are measured Differences are qunatitatively analyzed using statistics

Strengths of Intact Group Designs Practical Intervention not withheld or group not exposed to risk Helpful in applied settings (clinical) Easy to carry out Use secondary data

Weaknesses of Intact Groups Cannot draw definitive conclusions about cause & effect Data collection secondary Forfeits control over the independent variable Extraneous variables could effect outcome

Time Series Designs Measurement of a group over time Independent variable manipulated at some point in time Group serves as its own control Enable the researcher to: –Determine effectiveness of intervention –Quantify timing of effects

Characteristics of Time Series Designs Population of interest is identified Variables are defined Baseline condition is measured Intervention is applied Outcome variables are measured over time Differences in groups and time periods are analyzed quantitatively with statistics

Strengths of Time-Series Designs Fewer subjects required Effects of intervention over time can be quantified (good for lifestyle change interventions) Multiple data points before and/or after the intervention Can evaluate effects of change on a group, ie. organizational change

Weaknesses of Time Series Designs Inability to include a meaningful control group Cause & effect determination is weakened Rival explanations for observed outcomes Attrition can be a particular problem

Using Quantitative Research Useful in regards to: –Assessment & diagnosis of patients –Draw definitive conclusions regarding cause & effect (experimental design being the gold standard) –Can identify complications, side effects of an intervention –Evaluation of outcomes

Critiquing Quantitative Research Quantitative nature of study is clear Specific design is identified Rationale for design is linked to the research question Instruments & measurement procedures are described objectively Validity of instrumentation is described with supporting statistics

Critiquing Quantitative Research (Cont.) Reliability of instrumentation is described with supporting statistics Detailed protocol is described Threats to internal validity are identified & controlled Research bias & treatment effects are controlled by blinding Sufficient information is supplied as to whether the findings can be generalized