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.