Anatomy of Medical Studies: Part I. Emily D Agostino Epidemiology and Biostatistics CUNY School of Public Health at Hunter College

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1 Anatomy of Medical Studies: Part I!! Emily D Agostino Epidemiology and Biostatistics CUNY School of Public Health at Hunter College

2 I. Standard format of a Medical Study Abstract (quick overview: what was done, what was found, why it matters?) Introduction (how does this study contribute to what is known?) Methods (what was done?) Results (what measures were calculated?) Discussion (what was found within the larger context of the literature?)

3 Abstract Journal of publication (careful!) Authors (Lead- first; Principal investigator or department head-last) Quick overview of the study Best to avoid ONLY looking at the abstract WHY? Abstracts have strict word limits Abstracts do not tell the whole story Skimming articles for key points is a skill worth learning!

4 Introduction: Background/literature review, hypothesis, unique contribution of the study Literature review Hypothesis Unique contribution

5 Methods: Description of data set, data cleaning steps, analyses performed, missing values* Steps Dataset *Results may also include some of this information depending on the journal

6 Results: Measures calculated R: Correlation coefficient (a measure of the strength and direction of the linear relationship between two variables; Closer to 1= more strongly correlated)! P-value: Significance (the probability of obtaining a test statistic at least as extreme* as the one that was actually observed, assuming that the null hypothesis is true; p<.05 generally accepted) *An extreme test statistic is one that shows a difference between two groups/treatments/exposures, etc.

7 Graphs/Figures/Tables: Pay attention! Outliers

8 Discussion: Findings, study limitations, conclusions Confounding Causation vs. Association Externa l Validity

9 Exercise: Anatomy of a study from the Working in pairs, skim the article you have been assigned and complete the exercise. Be prepared to explain the fundamentals of your study to the class. literature

10 II. Study Designs What drives study design: Is the study prospective or retrospective? Are they studying a rare or common disease? Are they studying a rare or common exposure? Is it possible to have a control group? If so, who? (ex. environmental and behavioral exposures vs. clinical trials) What ethical questions are raised? What funding is available to conduct the study? How long can we wait for answers?

11 Experimental: Animal Research/In-Vivo Testing (using animal models) Clinical/Pharmaceutical/ Drug Trial (test a treatment) Randomized Controlled Trial (assigns participants randomly to an intervention) Common studies in medical science Observational/Descriptive: Cohort (follow group with particular exposures and look for outcomes) Case-control (select participants based on disease status and look for prior exposures) Cross-sectional (exposure and outcome data collected on a population or subset at one point in time) Case study (exploratory analysis of a particular person, group or events) Case/Clinical series (follow a group of patients after treatment or draw from medical records) Meta-Analysis (statistically combining results from multiple studies improve precision in estimating effects)

12 Hierarchy of medical studies Source: Center for Devices and Radiological Health (CDRH)

13 RCT s The Gold Standard of clinical studies Allow for causal inference Famous example: Hormone Replacement Therapy (HRT) and heart disease Source: Consort guidelines, 2010

14 HRT: HERS Study HRT initially thought to be protective against cardiovascular disease (CVD) 1998: Heart and Estrogen/progestin Replacement Study (HERS) findings released First major randomized clinical trial of HRT for secondary prevention of heart disease NO overall benefit of HRT BUT! Unexpected increased risk of heart disease during the first year of follow-up. Since then, many RCTs have confirmed these findings

15 HRT: Why did they change their mind? With respect to heart disease, the view of conventional HRT has migrated from a position of presumed benefit to one of proven harm. Source: Herrington D. Hormone Replacement Therapy and Heart Disease: Replacing Dogma With Data. Circulation. 2003; 107: 2-4 Observational vs. Experimental studies Association vs. Causation

16 Advantages of RCT s Randomization (participants are randomly assigned a treatment) Theoretically, equal distribution of confounding variables* across treatment groups (a.k.a. exchangeability) Temporality (we know the exposure proceeds the outcome) Control group (a.k.a. the counterfactual)! *Variables that could mask the true effects of the intervention on the outcome

17 Disadvantages of RCT s Ethical? (Has it first been tested in a cell culture or in animals??) Affordable? (May cost hundreds of millions of dollars!!) Blinded? Double blinded? (If not, how does this lead to bias??) Noncompliance? (What if a participant knows or suspects they are receiving the placebo treatment and finds other sources of treatment? What if people drop out?) Generalizable? (What were the exclusion criteria for the trial? Would people in the real-world comply in the same way? Just because it worked for this group ) Stable Unit Treatment Value Assumption (SUTVA) violations? (Are responses independent of other s treatment? Are responses due to the treatment assigned?) Epidemiology and Biostatistics. 20

18 Alternatives to RCT s Non-randomized controlled trials Single arm trials (no control group) Historical control (control group comes from historical records of patients similar to those with the intervention) Case-control, cohort, case studies, etc. (observational and descriptive studies)

19 Cross-sectional Studies: Snapshot - collect data at one time, asking a large sample about disease status and current or prior exposures Advantages: time-efficient, cost-efficient, can study a large/diverse population and many variables simultaneously Disadvantages: difficult to establish causality; how representative is your sample?

20 Cross-sectional Study: Example World Trade Center Health Registry (WTCHR), a cross-sectional study reporting on physical and mental WTC disaster-associated exposures and outcomes in individuals highly exposed to the WTC attacks >43,000 enrollees ( Wave 3 Survey) Provided a comprehensive look at health status 10 years after 9/11, including diabetes, asthma, and post-traumatic stress disorder.

21 Cohort Studies: Select participants according to their exposure status Follow them over time (prospective) Look for disease outcome! Exp DZ? No DZ?! No Exp? DZ? No DZ? Time Advantages: can look at many exposures/diseases at the same time, can establish causality if done well/have adjusted for confounders. Disadvantages: expensive, take time, loss to follow-up

22 Cohort Study: Example Framingham Heart Study (1948) Researchers recruited 5,209 men and women between the ages of 30 and 62 from the town of Framingham, MA Purpose: to identify the common factors or characteristics that contribute to CVD by following its development over a long period of time in a large group of participants who had not yet developed overt symptoms of CVD or suffered a heart attack or stroke. STILL going!

23 Case-control Studies: Select participants according to their disease status Ask them about prior exposures (retrospective)!! EXP? No EXP? EXP? No EXP? DZ No DZ TIME Advantages: time-efficient, cost-efficient, no minimal loss to follow-up Disadvantages: suffer from bias, difficult to establish causality, can't directly estimate the risk Epidemiology and Biostatistics. 2014

24 Case-control study: Example Tobacco smoking and lung cancer in patients from 20 London hospitals (Richard Doll & Austin Bradford Hill, BMJ 1950) Doll: The foremost epidemiologist of the 20th century A pioneer in linking smoking to lung cancer and heart disease, introduced scientific rigor to the field, stopped smoking after his own findings. Dose-response: "The risk of developing the disease increases in proportion to the amount smoked. It may be 50 times as great among those who smoke 25 or more cigarettes a day as among nonsmokers."

25 Exercise: Design a Study!

26 Chocolate and Cognition: Discussion What if an institution has a limited amount of funds to conduct an epidemiologic study will they still do an RCT? Why do you think cohort studies are not considered as scientific as randomized controlled clinical trials?

27 Summary & Conclusion Science never solves a problem without creating ten more. -George Bernard Shaw! Source: topic_science.html#pxp7ycjhtkr3lqwq.99

28 And remember All you need is love. But a little chocolate now and then doesn t hurt. -Charles M. Schulz Source: chocolate.html#pfb3ywuqpovlhwmp.99

29 THANK YOU! Contact information for Emily: Emily D Agostino edagosti@hunter.cuny.edu! Course evaluation: