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Para que servem os estudos observacionais?

Observational studies help researchers understand a situation and come up with hypotheses that can be put to the test in clinical trials. Observational studies can find associations between things but can’t prove that one thing causes another. Researchers do not do experiments or test new treatments; they observe.


Quais são os tipos de estudos observacionais?

Case Study/Case Series; Ecological Study; Cross-Sectional Study; Case-Control Study; Cohort Study.


O que são Case Study/Case Series?

A detailed description of one or more patients. By documenting new and unusual cases, researchers start to generate hypotheses about causes or risk factors.


O que analisa um Ecological Study?

Compares the rate of a disease or condition for groups of people, such as towns in different climates or with different average incomes.
Aims the society (ex: prevalence and incidence of Covid-19; identifying modifiable facteurs de risk, etc.) and not an individual in a specific condition (ex: individual treatment of arthrosis).
Ecological studies are particularly useful to generate hypothesis and trends.


O que é um cross-sectional study?

A snapshot of many people at one moment in time. These studies can show how common a condition is and help identify factors associated with it.


O que se faz num case-control study?

A group of people who have a condition is compared to a control group of people who don’t. Possible causes or risk factors can emerge.


O que se pretende com um cohort study?

A large group of people is observed over time. Some eventually develop a disease or condition. Researchers can learn how often the condition occurs and find possible causes or risk factors.


O que é feito nos Clinical Trials?

Researchers test new ways to prevent, detect, or treat disease. Treatments might be new drugs or combinations of drugs, new surgical procedures or devices, or new ways to use existing treatments. Clinical trials can also test other aspects of care, such as ways to improve the quality of life for people with chronic illnesses.


A well-designed clinical trial is the gold standard for proving that a treatment or medical approach works, but clinical trials can’t always be used. For example, scientists can’t randomly assign people to live in different places, or ask people to start smoking or eating an unhealthy diet. Quais são as fases dos clinical trials?

Phase 1: Find out whether a medical approach (e.g., drug, diagnostic test, device) is safe, identify side effects, and figure out appropriate doses; Typically fewer than 100 persons.

Phase 2: Start testing whether a medical approach works. Continue monitoring for side effects; get information that goes into designing a large, phase III trial; Typically 100-300 persons.

Phase 3: Prove whether a medical approach works; continue monitoring side effects; As many people as needed or able to enroll - can be 1,000 or more.

Phase 4: When a medical approach is being marketed, continue gathering information on its effects; Thousands of people.


How good are each type of study at showing cause and effect?

The strength of a study depends on its size and design. New results may confirm earlier findings, contradict them, or add new aspects to scientists’ understanding. In the end, cause and effect are usually hard to establish without a well-designed clinical trial.

Streght order: 1 Clinical Trial, 2 Case-Control Study/Cohort Study; 3 Cross-Sectional Study; 4 Ecological Study; 5 Case Study/Series.


Tips: Distinguish between case control and cohort?

Case control - There are cases (ex. already sick).
Cohort - follow differents groups with different exposures to see which on devellops the deasease/outcome.


Which type of studies can match this types of questions?
- Therapy
- Diagnosis
- Etiology/Harm
- Prognosis
- Prevention
- Clinical exam
- Cost

- Therapy: RCT > cohort > case-control > case series.
- Diagnosis: Prospective, blind comparison to a gold standard.
- Etiology/harm: RCT > cohort > case-control > case series.
- Prognosis: Cohort > case control > case series.
- Prevention: RCT > cohort > case-control > case series.
- Clinical exam: Prospective, blind comparison to a gold standard.
- Cost: Economic analysis.


Identify the types of validity.

Internal and external validity.


What are the 5 main factors that threat internal validity?

1. Chance (random error)
2. Bias (systematic error)
3. Effect-cause
4. Cause-effect
5. Confounding


Explain the purposes of an observational design.

- The purpose of observational studies is to collect information about events that have taken place or are
taking place in order to shed light on and understand a phenomenon, or to describe variables for future
- Evaluating the current status of the conditions of a group of persons
- Studies without human intervention
- Observational studies are designed to suggest that a predictor may be a cause of an outcome (e.g. eating
broccoli may reduce colon cancer)
- Experimental designs are often not feasible in epidemiology and non-experimental designs are often used
- The investigator will generally choose to observe an antecedent (is a precursor like an exposure suspected of affecting a result) and an outcome in a specific
- Cohort studies and case-control studies are two primary types of observational studies that aid in evaluating associations between diseases and exposures.


What are the main characteristics of the cohort design?

Population: Two or more subcohorts (exposed versus non exposed; outcome has not occured in any of the participants). In some cases a subcohort of non exposed is not easily identifiable (or expenseive) in these cases the exposed cohort is compared with a general population.

Focus on measuring the exposure of the participant to the particular deteminant. Other determinants still need to be measured as the determinant is often associated with other risk factors.

Follow up must be long enough.
Outcome is the number of incidence cases (ex: falls), often a continous variable.
Assessor should not have prior knowledge of the exposure status (being blinded (aveuglé))
Analisys of dichotomous outcomes: Rates, Risks, Odds.


Distinguish the cohort retrospective and the case-control.

Um caso-controlo vai comparar o passado de um grupo que desenvolveu o outcome e outro que não o desenvolveu (para procurar factores que desencadeiam o outcome).
O cohort retrospective vai estudar grupos que foram previamente identificados (ex. pacientes admitidos e não admitidos a um tratamento específico no passado) e avaliar o outcome nos grupos expostos e não expostos:
- the investigator might use existing medical records and go back in time several years to identify women exposed and not exposed to these technologies. He would then track them forward through records to note the birth outcomes. The study moves from exposure to outcome, though the data collection occurred after the fact.