How to live with observational studies

McCrindle, in Paediatric Cardiology Third EditionObservational Studies Observational studies are non-experimental in nature, whereby the phenomenon of interest is observed without imposing experimental or controlled conditions. They are highly variable regarding the quality and quantity of evidence they provide, and are fraught with potential bias and error. Carefully performed observational studies may be valuable in determining long-term outcomes and associated factors, in describing rare adverse events or rare disorders, and in determining the characteristics of diagnostic tests. Alternatively, hard-line proponents of evidence-based medicine will often reject offhand any type of observational study as inherently biased and of low validity.

How to live with observational studies

Although there are different systems, some of which take into account other aspects of quality including the directness of the research, the levels are designed to guide users of clinical research information as to which studies are likely to be the most valid.

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Likert-scales can be 5-point, 6-point, point, etc. Longitudinal study A longitudinal study is one that studies a group of people over time. Meta-analysis This is a mathematical technique that combines the results of individual studies to arrive at one overall measure of the effect of a treatment.

Narrative review A narrative review discusses and summarises the literature on a particular topic, without generating any pooled summary figures through meta-analysis.

This type of review usually gives a comprehensive overview of a topic, rather than addressing a specific question such as how effective a treatment is for a particular condition.

Narrative reviews do not often report on how the search for literature was carried out or how it was decided which studies were relevant to include. Therefore, they are not classified as systematic reviews. Negative predictive value This is one of a set of measures used to show the accuracy of a diagnostic test see sensitivity, specificity and positive predictive value.

The negative predictive value NPV of a test is a measure of how accurate a negative result on that test is at identifying that a person does not have a disease.

The NPV is the proportion of people with a negative test result who do not truly have a disease. The NPV for a test varies depending on how common the disease is in the population being tested.

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An NPV is usually lower false negatives are more common when disease prevalence is higher. These studies are sometimes called case-control studies nested in a cohort or case-cohort studies.

How to live with observational studies

The collection of data on the cases and controls is defined before the study begins. Compared with a simple case-control study, the nested case-control study can reduce 'recall bias' where a participant remembers a past event inaccurately and temporal ambiguity where it is unclear whether a hypothesised cause preceded an outcome.

It can be less expensive and time consuming than a cohort study. Incidence and prevalence rates of a disease can sometimes be estimated from a nested case-control cohort study, whereas they cannot from a simple case-control study as the total number of exposed people the denominator and the follow up time are not usually known.

Non-randomised study In this type of study, participants are not randomly allocated to receiving or not receiving an intervention. Observational study In an observational study, researchers have no control over exposures and instead observe what happens to groups of people. Odds ratio An odds ratio is one of several ways to summarise the association between an exposure and an outcome, such as a disease.

Another commonly used approach is to calculate relative risks. Odds ratios compare the odds of the outcome in an exposed group with the odds of the same outcome in an unexposed group.

Odds tell us how likely it is that an event will occur compared to the likelihood that the event will not happen. Odds ratios are a way of comparing events across groups who are exposed and those who aren't.

Run Your Own Field Studies

Open access Open access means that a study or article is available free-of-charge, usually via the internet. To access full articles in most medical journals you usually have to pay a subscription or make a one-off payment these types of articles are often referred to as paywalled content.Field research is conducted in the user’s context and location.

How to live with observational studies

Learn the unexpected by leaving the office and observing people in their natural environment. If you live north of the line connecting San Francisco to Philadelphia and Athens to Beijing, odds are that you don’t get enough vitamin D.

The same holds true if you don’t get outside for at least a minute daily walk in the sun. African-Americans and others with dark skin, as well as older.

Cohort studies and case-control studies are two primary types of observational studies that aid in evaluating associations between diseases and exposures. In this review article, we describe these study designs, methodological issues, and provide examples from the plastic surgery literature.

Consistent with the meta-analysis of observational studies and randomised trials, but in contrast to current dietary guidelines, we found that greater dairy consumption was associated with lower risk of mortality and cardiovascular disease.

Implications of all the available evidence. In laboratory and animal studies, the presence of increased levels of exogenous antioxidants has been shown to prevent the types of free radical damage that have been associated with cancer development.

Therefore, researchers have investigated whether taking dietary antioxidant supplements can help lower the risk of developing or dying from cancer in humans. Experiments vs Observational Studies: Definition, Differences & Examples observational and experimental studies.

An observational study is a study where researchers simply collect data based.

Observational Study - National Library of Medicine - PubMed Health