Medical Study Designs: Literature Reviews

Types of Research Designs

A systematic review of the medical literature. A systematic review is an examination and assessment of all research studies that address a certain clinical issue. The researchers use a systematic approach to gathering, assembling, and evaluating a body of literature on a certain issue by using a specified set of criteria. A systematic review generally includes a commentary of the findings of the research medical study. The systematic review might also include a meta-analysis, which is a quantitative data pooling. A comprehensive examination of women with breast cancer who use complementary and alternative medicine is one example. Clinical Journal of Oncology Nursing, August 2010;14(4):E45-55. A Wanchai, JM Armer, and BR Stewart.

A trial controlled by randomization is a well-planned clinical investigation in which volunteers are randomly assigned to one of two or more groups. There are several methods for randomly assigning medical study participants to groups. A randomized controlled trial comparing meditation and exercise to prevent acute respiratory infections is one example. Barrett, B., et al. Jul-Aug 2012;10(4):337-46. The Ann Fam Med.

A cohort study (also known as a prospective observational study) compares a group of people who are presently getting therapy for a disease to another group of people who are not receiving treatment for the condition. The multi-center prospective cohort study on the usage of smokeless tobacco in South Asian communities is one example. Addiction, 107 Suppl 2:45-52, December 2012. R. Croucher et al.

Case-Control Study
Case-control studies do not follow individuals across time; instead, they begin with the outcomes. Researchers choose people with a certain result (the cases) and conduct interviews or record checks to learn about the numerous experiences they had. They compare the likelihood of experiencing the consequence against the likelihood of experiencing it without. Proportional mortality, a case-control medical study exploring the relationship between bicycle helmet non-use and the risk of fatal head injury is an example. The Canadian Medical Association Journal, November 20, 2012, 184(17):E921-3. N. Persaud et al.

Cross-sectional research involves observing a specific population at a certain time or interval. The outcome and the exposure are chosen simultaneously. Fasting may not always be necessary before cholesterol screening, according to one example from a nationally representative cross-sectional study. Pediatrics, September 2011;128(3):463-70. MJ Steiner et al.

Series and Case Reports provide an overview of a group of patients who had notable results. There is no control group present. Consider the following case study on student mentoring in a service-learning clinical supervision context as an example. Phys Ther. Oct 2011;91(10):1513-24. JB Lattanzi et al.

Subject-matter experts provide editorials, thoughts, and views. As an example, consider health and medical care in the twenty-first century: universal access. American Journal of Public Health. 2006 Dec;96(12):2090-2. CE Koop.

Animals were utilized as study subjects in the investigations. In rats with diet-induced obesity (DIO), for example, intranasal leptin lowers appetite and increases weight loss. Endocrinology. Jan 2012;153(1):143-53.. C. Schulz, K. Paulus, O. Jöhren, and H. Lehnert.
In a controlled laboratory setting, “test tube” tests are performed.

Study Design Terminology

Any deviation from the truth in results or judgements, or in the processes that lead to such a distortion, is defined as bias. Bias may be caused by a variety of sources, including one-sided or recurrent variations from the true value in measurements (systematic error), flaws in study design, and errors in findings, interpretations, or analyses based on inaccurate data or data collection. Under these conditions, evaluating bias does not entail subjectivity or prejudice.

Case studies, often known as “control studies,” begin by identifying people with a specific disease of interest and a control (comparison, reference) group free of the sickness. The link between an attribute and the disease is studied by comparing persons with and without the illness in terms of the frequency or levels of the feature in each group.

Causation is the connecting of causes and outcomes. It is said to be essential when a cause must always occur before an effect. It is considered to be adequate when a cause initiates or induces an effect. Only a few of the variables that may be associated to the likely sickness cause or effect include predisposing, enabling, precipitating, reinforcing, and risk factors.

Groups under control: These are the groups used as a baseline for comparison in experimental studies. Despite the fact that they share many characteristics with the experimental group, they are not exposed to the experimental intervention.

Controlled clinical trials involve at least one control therapy, one or more test treatments, specified outcome measures for evaluating the intervention under research, and a bias-free mechanism for assigning patients to the test treatment. A drug, device, or procedure may be used as treatment if it has been shown to be effective in diagnosing, treating, or preventing illness. Control approaches include placebos, active drugs, no treatment, different dosage forms and regimens, historical comparisons, and so on. The investigations are known as Randomized Controlled Trials. Controlled trials are those in which patients are randomly assigned to test or control therapy using mathematical procedures such as a random numbers table.

A cost-benefit analysis compares a program’s costs against its expected returns in dollars (or another currency). The benefit-to-cost ratio measures the expected return on investment per dollar invested. In general, this method excludes consideration of characteristics that are not ultimately quantifiable in economic terms. Cost effectiveness is the comparison of several ways to achieving a certain set of objectives.

Studies that compare two or more interventions or therapies in which subjects or patients are switched to a different therapy after completing one term. Half of the people are randomly allocated to get the two treatments, A and B, in the order A, B, while the other half receive them in the opposite order. This design has been criticized because it allows the effects of the first treatment to persist into the time period of the second treatment.

Studies in which each participant in the study population or a representative sample is tested at a certain moment in time for the presence or absence of sickness or other health-related factors. LONGITUDINAL STUDIES, on the other hand, are those that are monitored throughout time.

The double-blind technique is a method of researching a treatment or procedure while keeping both volunteers and researchers in the dark about who is really getting which therapy.

Empirical research is the investigation of actual activities or the impact of actual practices or policies. Direct observation, statistical records, interviews, or experimental techniques are used.

Evaluation studies are works that incorporate study on the effectiveness or utility of methods, people, or equipment.
To identify markers linked to a specific disease or condition, a genome-wide association study compares the allele frequencies of every polymorphic marker currently available (or a representative sample across the entire genome) in unrelated patients with a specific symptom or disease condition and those of healthy controls.

Intention to Treat Analysis is a method used in randomized controlled trials to compare patients in the groups to which they were originally randomly assigned.

Logistic models are statistical representations of the relationship between an independent variable and a qualitative dependent variable (one with only discrete values, such as the presence or absence of a disease). Estimating a person’s risk (disease probability) as a function of a certain risk factor is a common use in epidemiology.

Longitudinal studies are those that follow variables relating to a single individual or a group of persons through time.
Participants in cohort studies who were “lost to follow-up” because they were unable or unable to attend follow-up visits had undetermined outcomes.

Individuals from a study group and a comparison group are individually paired with participants from the comparison group (for example, age-matched controls) to make the subjects comparable in unrelated features.

The term “meta-analysis” refers to works that use a quantitative approach to combine the findings of unrelated investigations (often taken from the published literature) and synthesize summaries and conclusions that can be used to assess treatment efficacy, design future experiments, and so on. It is often a summary of clinical trials. It differs from literature reviews in that the author or sponsoring organization will usually refer to it as a meta-analysis.

Numbers Needed to Treat – The number of patients who must be treated in order to avoid another negative outcome. So, the inverse of absolute risk decrease.

The odds ratio is the ratio of two odds. The exposure-odds ratio for case control data is the ratio of the chances of exposure among cases to the odds of exposure among noncases. The disease-odds ratio for a cohort or cross section is the ratio of the risk of sickness among those who have been exposed to those who have not. The prevalence-odds ratio is a cross-sectional odds ratio derived from studies of frequent occurrences.

Patient selection refers to the standards and criteria used to determine whether patients with certain issues should be included in prescribed treatment programs, as well as the standards used to choose participants for various clinical trials and other research operations.

Test Predictive Value – The predictive value of a positive test in screening and diagnostic tests is the likelihood that a person with a positive result is a true positive (i.e., has the disease); the predictive value of a negative test is the likelihood that the person with a negative result does not have the disease. The predictive value of a test is affected by its sensitivity and specificity.
Prospective studies are carried out by tracking a population for a sufficient number of individuals over a sufficient amount of time in order to compute incidence or mortality rates after selecting the study group.

Qualitative studies focus on the meanings and interpretations of participants and gather data via observation, interviews, or verbal interactions.

Quantitative research refers to studies that use numerical analysis.

A strategy employed in clinical trials and other sorts of research is to randomly assign experimental participants, whether human or animal, to treatment and control groups or within treatment groups. It may also be applied to inanimate object research.
Clinical trials with at least one test treatment and one control treatment, concurrent enrollment of the test and control treated groups, and follow-up of the test and control treated groups, and in which the treatments to be administered are chosen at random using a random-numbers table.

The statistical reproducibility of measurements, particularly in a clinical situation, including the examination of instruments or processes to achieve repeated results. This concept encompasses the reproducibility of physiological parameters, which may be used to develop criteria for assessing probability, prognosis, or response to a stimulus, as well as the reproducibility of a condition’s occurrence and experimental results.

Retrospective studies use data on the characteristics of the people under medical study or on earlier events or experiences to derive conclusions about an exposure to suspected causal factors. They are used in the evaluation of etiologic theories. The key point is that some of the study participants have the sickness or result of interest, and their characteristics are compared to those of unaffected people.

The sample size is the number of units (people, animals, patients, specific circumstances, etc.) in the population being studied. The sample size must be large enough to have a fair probability of detecting a true difference between two groups.

To assess test results, sensitive and specific binary classification measures are applied. The proportion of true positives is referred to as the sensitivity or recall rate. Specificity refers to the chance of correctly recognizing the absence of a condition.

A single-blind strategy is one in which neither the observer nor the subject is aware of their group assignment.

Time variables are discrete time period components that impact certain outcomes or conditions.

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