Presentation on theme: "INTRODUCTION TO SCIENTIFIC PAPERS"— Presentation transcript:
1 INTRODUCTION TO SCIENTIFIC PAPERS Joe Pozdol, MLISEvans Whitaker, MD, MLISNorris Medical LibraryUniversity of Southern California2003 Zonal Ave.Los Angeles, CA
2 Before We Begin…Ask!PowerPoint at under Key Resources for StudentsInteractive questionsHandoutsArticle laterEvaluationUnwanted handouts
3 Outline For TodayI. Parts of a paper A. Abstract B. Introduction/Background C. Methods D. Results E. Discussion F. References (Bibliography) II. Study types A. Primary 1. Observational 2. Experimental B. Secondary III. Group work IV. Evaluations
22 Part II Objectives Learn the common study types Be able to extract the research questionBe able to identify an article’s study typeBe able to determine the conclusions
23 Outline For This Section Focus on 4 study designsCase-controlCohortRandomized Control TrialReviewNarrativeSystematicMeta AnalysisThere are others but these are the main four; two others are mentioned in your handout
24 “3 questions to get your bearings” * What was the research question?What was the research design?Was the research design appropriate to the question?Will try to find answers to 1 and 2 in excerpts of 4 articles (A-D) providedThese three questions can be asked of any research study.What was the research question?Why was the study needed? (Another way to say “Was the study original? Does it add to our understanding?”What was the research design?Was the research design appropriate to the question?** - Greenhalgh, T. (2006). How to read a paper: the basis of evidence-based medicine. Malden, MA: Blackwell24
25 Study Designs Primary Literature Secondary Literature Observational Case-ControlCohortExperimentalRandomized Control TrialSecondary LiteratureNarrative (Subject/Journalistic)ReviewsSystematic ReviewMeta AnalysisObservational means that the researcher does not choose which group a subject is part of – the experimenter observes the subjects as they are and does not manipulate the assignmentExperimental means that the researcher assigns subjects to an experimental or control groupMany ways to organize this information.This is one way that makes sense to me.Secondary literature is a summary of primary literature.Narrative, Subject, or Journalistic Reviews -- subject to author biasSystematic Review – a transparent, well-defined methodology is used to select and analyze a group of articlesMeta Analysis – similar to above but using statistical methods to combine results of studiesPrimary literature reports the individual investigations/experiments.Primary literature can be divided in two groups:Observational in which the investigator does not control what exposures the subjects have.Experimental in which the experimenter controls exposures that the subjects have.Retrospective looks at previously collected data. May apply to case-control, cohort. It is possible to do retrospective analysis of data from an experiment (questionable practice).Prospective data is collected moving forward in time.Cross-sectional – usually applied to case-control (or cross-sectional) studies.Data are collected at a point in time for a group of subjects.Longitudinal - data is collected over time for a group of subjectsBlinding applies to experimental design:1. the subject does not know whether he/she is in the treatment or the control group.2. the experimenter who measures outcomes does not know which subjects are in which group.1 only = Single blind1 and 2 = Double blindCross over – subjects act as their own controls.Usually there is a “wash out” period between phases.Qualitative studiesSecondary literature – see above25
26 Case-Control Patients with a disease or exposure --compared to-- Similar group without disease or exposureBest usesRare conditionsDiseases or conditions that may take a long time to develop
27 Background: DES Used in the United States from 1947 until 1971 Boston area doctors noted an unusual cancerStudy compared the group with the cancer to similar people without the cancerThe major difference between the cases and the controls was DES exposureDES is an estrogen approved by US FDA in 1947 to prevent spontaneous or habitual abortion.Two large trials showed it to be ineffective for its proposed uses in Despite this it was used ‘til ‘71 in US and mid-to-late ‘70s in Europe.In late ‘60s, 8 cases of clear-cell adenocarcinoma (CCAC) of the vagina were reported in women in their teens and twenties. This tumor type had not been seen in this age group before; the cancer was rare in any case and almost always found in those >50.These “cases” of CCAC were compared to other women of same age without CCAC. The use of DES by the case’s mothers during pregnancy was found in the CCAC women but not in the controls.The Case Control study was completed in months, reported in If the researchers had used other methods it might have taken 20 years to show the relationship between DES and CCAC.27
28 Example: DES and Cancer Herbst, A.L., Ulfelder, H., & Poskanzer,D.C. (1971). Adenocarcinoma of the vagina: association of maternal stilbestrol therapy with tumor appearance in young women. NEJM, 284(16),Look at article:Last sentence in Introductory area = research questionFirst paragraph in methods = research design“case-control retrospective study” – clearly labels itself as a case-control study“four matched controls for each patient…were selected by examination of birth records”. “Females born within 5 days and on the same type of service”.
29 Why did the authors match cases and controls by the type of service mothers received?* * -see page 879To reduce socioeconomic differencesTo examine whether the cancer was related to infectious disease exposuresTo decide if chemical disinfectants used to clean wards caused cancerAll of the above
30 How many of the 8 cases’ mothers were given estrogen in pregnancy (DES)? AllSevenFiveThreeOneNone30
31 Cohort Two groups compared over time One group with “exposure”, the other without the “exposure”Best used:when exposures can’t be controlledwhen outcomes occur infrequentlywhen RCT is not ethicalExposure is a broad term, can be a…DrugEnvironmental exposureGenetic inheritance (parent or parents with a disease; subject with known genetic variant)31
32 Example: Smoking vs. Non-Smoking British Physicians Doll, R., Peto, R., Boreham, J., & Sutherland, I. (2004). Mortality in Relation to Smoking: 50 years' observations on male British doctors. BMJ, doi: /bmj AE50 years (and counting) Cohort Study of British doctorsMost recent of a series of reportsCompared health outcomes of smokers vs. health outcomes of non-smokersResearch question =Research design =Amazing study of British MDs now followed for 50 years with 94% follow-up of those still living study ended in 2005Notice this article never proclaims itself as a cohort study.Compared health outcomes of smokers vs. health outcomes of non-smokersReports:1954, 1956, 1964, 1976, 1994, 2004.35,000 MDs at outset, 10,000 died in first 20 years, 10,000 in the next 20 years, another 5,000 in the last 10 years. Men who smoked throughout the study died on average 10 years earlier than non-smokers.32
33 When was there enough evidence from this study to show the link between smoking and lung cancer? 1954196619781991
34 Randomized Control Trial A treatment group is compared to a control groupGroup members are assigned randomlyBest uses:Drug therapiesMedical treatments“Cross over” means that subjects become their own controls.Placebo control means that a placebo was used on the control group and compared to an active treatment for the treatment groupSingle blind means that the subjects did not know which group they were in – control or treatmentDouble blind means that both the investigators and subjects did not know which group the subjects were part of.
35 Example: Smoking cessation intervention An, L.C., Klatt, C., Perry, C.L., Lein, E.B., Hennrikus, D.J., et al. (2008). The RealU online cessation intervention for college smokers: a randomized control trial. Preventive Medicine, 47(2)Look at the article:The last paragraph of the introduction - research questionThe last paragraph of the introduction - research designStudy flow chart - pg. 196As you can see this study tells you the study type in the title, and in the abstract. It does not say RCT in Methods?Notice the study flow sheet on page 196
36 25,000 UM students were recruited by email How many UM students ended up in the intervention group? 1. 24,0072. 2,4075. 7
37 What percent of RealU participants had 30 days of no smoking at week 30? 100%80%60%40%20%none30
38 Narrative (Journalistic/Subject) Reviews The “traditional” or “classic” review“Review” limit in Ovid/PubMed includes:Narrative reviewsSystematic reviewsAuthors choose articles includedAuthor bias is a concern – research verifies this effectWhen you search MEDLINE you can cut down your number of articles by only including reviews.38
39 Systematic ReviewReproducible methods to find and select articles are includedShould include both inclusion and exclusion criteriaWhy? Decrease author bias
40 Example: Is HPV Vaccine Cost-Effective? Techakehakij, W., Feldman, R.D. (2008). Cost-effectiveness of HPV vaccination compared to Pap smear screening on a national scale: a literature review. Vaccine, doi: /j.vaccineLook at article:Pg. 2, Section 3.1, first paragraph = research questionPg. 3, Section 4.1, first to third paragraphs = research designThe essence of this article is that cervical cancer remains a killer of a quarter million women a year almost all in the developing world.Two HPV vaccines have been released on the market in the last few years but remain quite expensive, although appear effective.PAP smears have been used for the last 65 years to test women for cervical cancer.The test has problems with the ability to detect problems (low sensitivity) but widespread use in the US has decreased cervical cancer mortality by >70%.How do we decide whether to begin a cervical cancer immunization program?That study examines cost-effectiveness – does the cost of the vaccination program save money compared to the costs of a PAP smear program. The analyses attempt to factor in the obvious costs (cost of the programs), and the less obvious costs (failed vaccines, cost of cancer treatment, incomplete screening and vaccination).
41 It is recommended that HPV vaccine be given as a 3 shot series It is recommended that HPV vaccine be given as a 3 shot series. How much do 3 doses of vaccine cost?$500-$1000$300-$500$200-$300$100-$20030
42 Meta Analysis Similar to Systematic Review except… Numeric data from separate studies combined in meta analysisUses statistical/mathematical methods to combine numerical data from studiesCombining data increases the confidence we have in the conclusions reached by a meta analysis
44 Group WorkGroups of 3Everyone in group gets same article (#1, 2, 3, OR 4)Spend 10 min. working together on questionsClass discussionOne article from each of these four types:Case-controlCohortRandomized control trialSystematic review
46 What kind of question is it good for? Identifying Characteristics Article TypeWhat kind of question is it good for?StrengthsWeaknessesIdentifying CharacteristicsCase-Control(Herbst, 1971)(Peled, 2008)-Rare disorders or conditions-Slow developing disorders-Causation*-Short time frame to examine correlations between disorder and other factors-Susceptible to bias-Limited validity-Cross sectionalCohort**(Doll, et al, 2004)(Metcalf, 2008)- Prognosis- Feasible when studying conditions or exposures over which the investigator has no control-May require large groups, long durations, great cost-Longitudinal-Usually prospective-Can be retrospective (less cost)Randomized Control Trial (RCT)(An et al, 2008)(Gordon, 1997)-Drug treatment-Medical interventions-Strong level of evidence-Low susceptibility to bias-Feasibility (e.g. Ethical limitations)-Generalizability**-Randomization method -Experimental and control groupsSystematic Review (Techakehakij,2008)(Gallicchio, 2008)-Strongest level of evidence-Many topics have no systematic review-Methods section has explicit information about information sources, how articles were chosen or excluded* - used loosely here; not distinguishing between correlation and causation(in medicine etiology is used for the cause of a disease or condition)** - can results of an RCT be applied to groups that do not match the study group?
47 Used for Evidence-Based Medicine The Evidence PyramidUsed for Evidence-Based Medicine
48 Thanks for your attention We will post these slides on the Student Portal on the Norris Medical Library websiteContact us with questionsJoe Pozdol –Evans Whitaker –Please complete evaluations!
49 ReferencesAn, L.C., Klatt, C., Perry, C.L., Lein, E.B., Hennrikus, D.J., et al. (2008). The RealU online cessation intervention for college smokers: a randomized control trial. Preventive Medicine, 47(2)Doll, R., Peto, R., Boreham, J., & Sutherland, I. (2004). Mortality in Relation to Smoking: 50 years' observations on male British doctors. BMJ, doi: /bmj AEGallicchio, L., Boyd, K., Matanoski, G., et al. (2008). Carotenoids and the risk of developing lung cancer: A systematic review. Am.J.Clin. Nutrit., 88,Gordon, C.M., Carey, M.P., & Carey, K.B. (1997). Effects of a drinking event on behavioral skills and condom attitudes in men: Implications for HIV risk from a controlled experiment. Health Psychology, 16(5),Greenhalgh, T. (2006). How to read a paper: the basis of evidence- based medicine. Malden, MA: Blackwell.Guyatt, G., Rennie, D. (eds.). (2001). User’s guides to the medical literature: essentials of evidence-based clinical practice. Chicago: AMA Press.
50 ReferencesHerbst, A.L., Ulfelder, H., & Poskanzer,D.C. (1971). Adenocarcinoma of the vagina: association of maternal stilbestrol therapy with tumor appearance in young women. NEJM, 284(16),Metcalf, B.S., Voss, L.D., Hosking, J., & Wilkin, J.T. (2008). Physical activity at the government-recommended level and obesity- relatedhealth outcomes: a longitudinal study (Early Bird 37). Archives of Diseases of Childhood (Early Bird 37). 93,Peled, R. Carmil, D., Siboni-Samocha, O., & Shoham-Vardi, I. (2008). Breast cancer, psychological distress and life events among young women. BMC Cancer, 8,