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# Nur3052 ch5

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### Nur3052 ch5

1. 1. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 5: Critically Appraising Quantitative Evidence for Clinical Decision Making
2. 2. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Critically Appraising Quantitative Studies • The process focuses on three questions 1. Are the results of the study valid? (Validity) 2. What are the results? (Reliability) 3. Will the results help me in caring for my patients? (Applicability) • Interpretation of results requires consideration of the clinical significance of the study findings and the statistical significance of the results
3. 3. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Question of Validity • Bias - anything that distorts study findings in a systematic way and arises from the study methodology − Selection bias − Knowledge of who is or is not receiving an intervention − Measurement bias − Recall bias − Contamination
4. 4. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question • Tell whether the following statement is true or false. • The best way to prevent selection bias is to randomly assign study participants to groups.
5. 5. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer • True • Rationale: Selection bias in quantitative studies is best controlled by assigning participants to groups on a random basis. Other systematic and deliberate methods of assignment normally increase the chance of selection bias.
6. 6. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Question of Validity (cont’d) • Confounded Study Results − A study’s results may be confounded when a relationship between two variables is actually due to a third, either known or unknown variable − Often encountered in studies about lifestyle and health − Frequently a result of participant history
7. 7. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Reliability • Evaluate whether the sum of all n values equals the original N • Magnitude of the effect − How strong is the difference between groups? − Tables − Statistical tests
8. 8. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Reliability (cont’d) • Strength of association − Absolute risk reduction (ARR) − Absolute risk increase (ARI) − Relative risk (RR) − Relative risk reduction (RRR) − Odds ratio (OR) − Number needed to treat/harm (NNT/NNH)
9. 9. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question • The findings of a quantitative study testing a high school-based sexual health program reveal that for every 140 female students who take the program, one pregnancy is prevented. This conclusion indicates the: a. OR b. NNT c. NNH d. ARR
10. 10. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer • b. NNT • Rationale: The number needed to treat (NNT) represents the number of people who would need to receive the therapy or intervention (the educational program) to prevent one bad outcome (teenage pregnancy).
11. 11. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Reliability (cont’d) • Random error − Variations that occur purely by chance − The extent to which random error may influence a measurement can be reported using statistical significance (or p values) or by confidence intervals.
12. 12. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Reliability (cont’d) • Statistical significance − The aim of statistical analysis is to determine whether an observed effect arises from the study intervention or has occurred by chance − Study hypothesis and null hypothesis − The smaller the p value, the less likely the null hypothesis is true − Confidence interval - describes the range in which the true effect lies with a given degree of certainty
13. 13. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Confidence Intervals
14. 14. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Questions to Ask in a Critical Appraisal • Why was the study done? • What is the sample size? • Are measurements reliable and valid? • How were the data analyzed? • Did any untoward event happen during the study? • How do the findings fit with previous research? • What does this mean for practice?
15. 15. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Appraising Case Studies • Historically ranked lower in the hierarchy of evidence • Must be used with caution to inform practice, and any application requires careful evaluation of the outcomes
16. 16. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Appraising Case Control Studies • These investigate why certain people develop a specific illness, have an adverse event with a particular treatment, or behave in a particular way • Questions to ask − How were the cases obtained? − Were appropriate controls selected? − Were data collection methods the same for the cases and controls?
17. 17. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Appraising Cohort Studies • These are used for investigating the course of a disease or the unintended consequences of a treatment • Questions to ask − Was there a representative and well-defined sample of individuals at a similar point in the course of the disease? − Was follow up sufficiently long and complete? − Were objective and unbiased outcome criteria used?
18. 18. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Appraising Cohort Studies (cont’d) • Did the analysis adjust for important prognostic risk factors and confounding variables? • What is the magnitude of the relationship between predictors (i.e., prognostic indicators) and targeted outcome? • How likely is the outcome event(s) in a specified period of time? • How precise are the study estimates?
19. 19. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question • A team of researchers have received a grant to investigate the potential links between diet and the development of stomach cancer. What methodology is most likely to answer the researchers’ clinical question? a. Case control b. Case study c. Randomized controlled trial (RCT) d. Qualitative study
20. 20. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer • a. Case control • Rationale: A case control study often selects individuals with a particular disease (e.g., stomach cancer) and looks back to identify factors that may underlie that disease (e.g., diet). Neither a case study nor a qualitative study would inform this relationship and an RCT would be unethical and impractical.
21. 21. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Appraising Randomized Controlled Trials (RCTs) • These can accurately establish cause and effect and can inform the efficacy and effectiveness of interventions • Questions related to validity of RCTs − Were the subjects randomly assigned to the experimental and control groups? − Was random assignment concealed from the individuals who were first enrolling subjects into the study? − Were the subjects and providers kept blind to study group?
22. 22. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Appraising the Validity of RCTs • Were reasons given to explain why subjects did not complete the study? • Were the follow-up assessments long enough to fully study the effects of the intervention? • Were the subjects analyzed in the group to which they were randomly assigned? • Was the control group appropriate? • Were instruments valid and reliable? • Were the subjects in each of the groups similar on demographic and baseline clinical variables?
23. 23. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Appraising Systematic Reviews • Systematic reviews are a compilation of similar studies that address a specific clinical question • Not the same as a literature review or narrative review • The process the was used to conduce the review should be explicit • Look for a detailed description of the databases accessed, the search strategies, and the search terms • Clinicians should be able to clearly see which studies were included and which were excluded and how selected studies were assessed
24. 24. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Appraising Systematic Reviews (cont’d) • The report should inform clinicians about how data were extracted from the individual studies • It should provide an overview of the evaluation of the included studies • Meta-analysis − The statistical approach to synthesizing the results of two or more studies − A relatively new methodology that has become a hallmark of EBP • As with all methodologies, applicability must be considered
25. 25. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Evaluation and Synthesis of Quantitative Studies • Once studies have been selected, they should be melded together into a synthesis upon which to base practice and standards • Individual studies should be evaluated using an evaluation table - see Table 5-8 • Synthesis is not reporting the findings of study after study; it is combining, contrasting, and interpreting a body of evidence to reach a conclusion
26. 26. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question • Tell whether the following statement is true or false. • Meta-analysis results in evidence that is applicable to a larger patient population than individual studies.
27. 27. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer • False • Rationale: In meta-analyses, combining the results of several studies produces a larger sample size and thus greater power to accurately determine the magnitude of the effect. This does not, however, increase the size of the relevant patient population.