Medical Statistics – Part 8: Study Types in Medical Research

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Study types in medical research Do you know the number of clinical decisions
a physician has to make daily? Most likely somewhere around 100 to 200. For example, if you request specific diagnostic
tests in a case with an uncertain diagnosis, a diagnosis can be made based on the results
and the most appropriate treatment option. But the most important thing is to involve
patients in the decision-making process. Physicians should not only make decisions
based on how they feel but also use reasoning, making decisions according to evidence-based
data. One of the most important bases in the decision-making
process in medicine is research studies. When reading the medical literature, you can
get easily confused by the different types of studies. In this Chalk Talk episode, which continues
our series on statistics, we’ll be explaining how to classify studies in medical research
to provide you with a better overview. In medical research, a general differentiation
is made between primary research and secondary research. Primary research involves the collection of
new data based on studies. In contrast, secondary research focuses on
using pre-existing data to answer and interpret specific questions from primary research,
which are summarized in meta-analyses or reviews to derive a conclusion with increased power. Basic research, also termed experimental studies,
can be differentiated into theoretical and applied research. Theoretical research can be divided into three
areas: analytical measuring techniques, imaging, and test development. In contrast, applied basic research involves
animal studies and cell culture experiments as well as studies on material development. If, for example, a new artificial joint for
replacement is to be launched on the market, initial experimental studies on the suitability
of the material used are performed. So, as you can see, basic research mainly
takes place in the lab. This can sometimes be problematic as lab conditions
can’t always be translated to the human body. In this case, clinical and epidemiological
studies in which the patient is at the foreground can be quite helpful. These can be differentiated into interventional
and observational studies. Interventional studies intervene directly
in the study participants’ lives. Some study participants receive an “intervention”,
which can be, for example, a new drug or surgical procedure. The effect of this intervention is subsequently
monitored. Clinical drug trials are of great importance
for the development and testing of drugs. These can be classically divided into four
phases. Phase one trials investigate the pharmacokinetic
and pharmacodynamic properties of a drug in the body. These studies are generally performed in healthy
individuals. Of particular interest is the maximum tolerable
dose of the drug. However, there’s one exception, namely in
oncology. Many drugs are so toxic that they can’t
be tested on healthy individuals. In such cases, phase I studies are often performed
in cancer patients with a very poor prognosis. Phase II trials aim to test the efficacy of
a new drug. Not only are healthy individuals examined
but also diseased individuals. Approximately 50 to 300 participants are recruited
in such studies. Phase II trials are concerned ultimately in
whether a drug shows promising efficacy to such an extent that further randomized studies
are warranted. Phase III trials investigate a drugs’ efficacy
in a large number of patients with a specific disease compared to a placebo group or patients
undergoing a current alternative treatment. To do so, a randomized controlled trial, in
short RCT, is usually performed. Randomized controlled trials are one of the
most important study designs in clinical trials. We’re pretty sure you’ve come across them
at some stage. Following the successful completion of phase
one to three trials, the drug can then be submitted for approval. However, even after being launched onto the
market, additional studies, termed phase IV trials, are performed to ascertain potential
long-term side effects of the drug. Since most of these studies are observational
in nature, we’ve decided to place phase IV trials to observational studies in the
chart shown. One special case in clinical trials is the
clinical testing of medical products. In such cases, the manufacturer needs to prove
based on clinical data that their product is safe and delivers the guaranteed benefit. In general, there are many rules and quality
criteria for performing clinical trials, which are discussed in further detail in our
library. Apart from clinical interventional studies,
there’s another study type: non-interventional observational studies. Here, study participants are under observation
and examined for specific criteria, such as whether smokers have a greater risk of developing
lung cancer than non-smokers. In prognostic studies, the effects of specific
factors such as age, pre-existing conditions, tumor stage, and disease course are determined. If a cancer patient asks, for example, “How
good is my prognosis?”, then several factors play an important role, such as the number
of lymph nodes affected as well as tumor size. Such correlations are analyzed in prognostic
studies. Also, they’re always prospective in nature. Now, let’s move on to diagnostic test studies. In these studies, an investigative procedure
is compared to an already established method, usually the diagnostic gold standard, and
its performance is assessed. For example, a diagnostic study can be used
to investigate which imaging procedure is best for diagnosing a herniated disc: an MRI,
a CT scan, or electromyography. In case series, several similar patient cases
with similar conditions are observed; however, there is no control group for comparison. Here’s an example: After the discovery of
HIV, 1000 patients were followed for common complications as part of a case series. Now on to epidemiological studies. They’re performed to analyze in further
detail the following aspects of diseases: Frequency, distribution, changes over time,
and cause. Analogous to clinical studies, a differentiation
is made between interventional and observational studies, with observational studies in the
clear majority in epidemiological research. But let’s take a look at epidemiological interventional
studies: These include field trials and group trials. In field studies, raw data is collected on
individuals in the same region. For example, let’s assume that the region
is located in an iodine-deficient area. If we now examine the addition of iodine to
table salt as a preventive measure against iodine deficiency syndrome, this field trial
would be experimental, with table salt iodization considered an intervention. If the intervention is allocated to groups
of subjects, the study is a group trial. A type of group trial is a community trial,
which is similar to a field trial but follows entire communities instead. For example, following communities who implement
lifestyle changes to prevent cardiovascular disease. But most epidemiological studies are observational. Depending on the question, there are different
types of studies: cohort studies, case-control studies, or cross-sectional studies. Further details can be found in our library. We want to finish off with a few words on
secondary research. Do you know how many scientific publications
are published annually? Well, it’s around more than 2 million worldwide. So, how can you keep track of so many publications? This is where secondary research comes in,
which involves reviewing and reassessing previously published studies. A systematic review has its name because studies
on a defined question are collected and evaluated in advance through predefined, systematic
methods. Meta-analysis is a term used to describe the
statistical analysis of data from multiple studies. They are mainly performed in studies with
very similar and homogeneous results. The effect size of individual studies are
summarized, leading to an answer supported by a great deal of evidence: Does the intervention
have an effect? If so, how large is this effect? If you’re on the lookout for high-quality
reviews, the best known and most used is the Cochrane Library. It was created in 1993 by the British physician
Sir Cochrane and includes a collection of databases containing high-quality, independent
evidence to communicate clinical decision-making. So, we’ve just introduced you to several
study types in medical research. But there are more study types than those
mentioned in this episode. The most important ones to remember are the
phase one to IV trials, cohort and case-control studies, as well as meta-analysis and reviews. If you’d like to test your knowledge on
the study types, then stay put for the quiz.

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