The process of evidence-based practice?
1) Ask an answerable question
2) Access the evidence
3) Appraise the evidence
4) Apply the appropriate evidence
5) Assess the process
How is a bias caused?
- extraneous variables may effect study variables
- may MASK or INCREASE effect of independent variable
- bias matters as we may not get the truth.
What does bias threaten?
Validity. Also affects confidence in study findings.
What are types of bias in quantitative research studies?
- systematic error (something that happens b/c of some things that are done systematically)
- can occur from: choice of study design, methods, analysis, reporting, interpretation
- conscious or subconscious
What is the goal in quantitative research?
- minimize extent of bias that may affect the outcome – what criteria of merit does this address?
- look at how different designs minimize bias
8 threats to internal validity (Campbell and Stanley)
*review threats to external validity
- history
- maturation
- testing
- instrumentation
- statistical regression
- selection biases
- experimental mortality
- selection - maturation interaction
True Experimental Designs
Randomized Control Trial
- elements: randomization, control group, manipulation (when the investigator puts the intervention in place) *** quiz
Quasi Experimental Design
Variations on RCT, but w/o randomization
- no random assignment of participants to groups –> participants from ‘intact’ groups available to the researcher (ex: exercise class)
or ‘matched’ groups (age, gender, height, weight)
Pre-experimental Designs
Non-randomized, used to collect preliminary information.
- characteristics: no random assignment, may not have control
- elements: intervention and outcome
- can’t say intervention caused the outcome
Notation symbols
R
R = random sample selection
*any r is random allocation
Notation symbols
r
r = random assignment
*any r is random allocation
Notation symbols
O
O = outcome - observation or measurement
Notation symbols
X
X = intervention or exposure to an experimental variable for which the effects are to be measured (*manipulation)
When are quasi-experimental designs most valuable?
When you can’t randomly allocate, better to do a group all together, ethics issues
When are pre-experimental designs most valuable?
- answering a level 1 question - can describe intervention and outcome, can’t say intervention caused O
- pilot testing an intervention protocol or measurement approach (exploratory)
Elements of Observational Studies (epidemological studies)
- researcher does not provide the intervention (no manipulation)
- comparison group
- naturally - occurring (not randomized groups)
What level question do you answer with descriptive studies?
Level 1
What level question do you answer with analytic studies?
Level 3 - cause and effect
What are observational studies called?
- cohort study - fwds in time
- case - control study - backwards in time
- cross- sectional (analytic) - interaction
Why are they different?
the direction of the outcome they provide
What is a cohort study?
- prospective - measure fwd in time - outcome measured after intervention
What is a case-control study?
- retrospective - start with outcome, then look back in time if they were exposed to the treatment
What is a case study or case series?
prospective
- target population - treatment, treatment effect
- measure these two things w/ no control
What is the world view for quantitative research?
- only one reality - looking for the truth
