An observational study is a study in which the investigator cannot control the assignment of treatment to subjects because the participants or conditions are not directly assigned by the researcher.
In an experimental study, the investigators directly manipulate or assign participants to different interventions or environments
Experimental studies that involve humans are called clinical trials. They fall into two categories: those with controls, and those without controls.
Definitions taken from: Dawson B, Trapp R.G. (2004). Chapter 2. Study Designs in Medical Research. In Dawson B, Trapp R.G. (Eds), Basic & Clinical Biostatistics, 4e. Retrieved September 15, 2014 from https://accessmedicine.mhmedical.com/book.aspx?bookid=2724
Types of studies | AP Statistics | Khan Academy
What are the different types of studies?
The types of research studies refer to the different methods for obtaining data. How researchers collect information and what information they collect depend on their goals and the questions they are trying to answer. Different types of research study designs are better suited for certain research questions.
For instance, researchers may want to know what scientific knowledge is available on a certain subject, like the effect of pet ownership on anxiety levels. These researchers may choose an observational approach, such as a meta-analysis or systematic review of literature on the topic. Other researchers may design an experimental study to test the effects of a new medication on a particular disease.
Common types of studies
Here are six common types of research studies along with examples that help explain the advantages and disadvantages of each:
A meta-analysis study is designed for researchers to compile the quantitative data available from previous studies. It is a type of observational study in which the researchers do not manipulate variables. Instead, they observe and analyze the data using statistical methods. For example, researchers may look at all the studies involving smoking cessation and longevity.
The main advantage of meta-analysis is that it is comprehensive, creating a report on all relevant findings for a specified research question. This is useful for making hypotheses based on previous outcomes. For instance, one study may link smoking cessation to increased longevity, but it may only have 15 participants. This sample size is not as useful scientifically. However, a meta-analysis study may discover 150 similar studies with similar outcomes, making the relationship between smoking cessation and increased longevity more probable.
The disadvantage of meta-analysis is that it does not provide new information for the related industry or field. Rather, it presents a thorough compilation of previous evidence.
2. Systematic review
A systematic review is designed to examine all the literature related to a specific research question in a standardized way. Systematic reviews aim to put relevant data into a more organized collection and to identify opportunities for further research on a topic. Systematic reviews are similar to meta-analysis studies in their techniques, but meta-analysis is concerned with quantitative data, and systematic reviews focus on outlining and combining all the findings from a thorough assessment of previously published studies.
For example, a systematic review may look at all the studies done on businesses implementing a four-day workweek. Researchers will locate all the studies related to shortened workweeks and summarize the studies and their findings.
The advantages of systematic reviews are:
Like meta-analysis, the disadvantage of systematic reviews is that they do not provide new information.
3. Randomized controlled trial
A randomized controlled trial is a type of controlled clinical trial that uses randomization techniques to assign participants to a group. A controlled clinical trial is used to test the effectiveness of a treatment, device or procedure versus receiving no treatment or a different treatment.
Participants are chosen based on certain criteria, aligning with the purpose of the study. For example, testing a new chemotherapy drug requires participants diagnosed with cancer. Other studies may target a certain age range, gender or other diagnoses.
Once participants are chosen for a randomized controlled trial, they are randomly assigned to a group, which may be one of the following:
The length of controlled clinical trials varies depending on the nature and purpose of the study. For example, a study testing allergy medication may last a year, while a study testing a new sleep device may last a month.
In each experiment, researchers control the variables related to the outcomes, providing the intervention being tested to one group in the study. Consider the allergy medication study. One group receives the new medication, another group may receive a placebo and the third group may act as the control group and receive no medication. Symptoms can be monitored at regular intervals throughout the course of a year.
Randomized controlled trials have the following advantages:
Randomized controlled trials have the following disadvantages:
4. Cohort study
A cohort study examines different groups of people, or cohorts, to determine possible trends over time. Researchers do not control or manipulate variables. Instead, groups are chosen based on shared features, such as exposure to a chemical, participation in an event or members of a certain group. Researchers then monitor the different groups and track their desired metrics, such as incidence of disease or job satisfaction.
For example, researchers interested in the effects of regular exercise on job performance may designate two groups between 25 and 35 years old: one group that exercises at least three days a week and another group that exercises less than three days a week.
Researchers survey the participants once every three months about their job performance, promotions, raises and other factors. After two years, researchers can compare the job performance outcomes of regular exercisers versus those who did not exercise regularly to determine if a correlation between exercise and job performance is present.
The advantages of a cohort study are:
The disadvantages of a cohort study include:
5. Case control studies
Case control studies analyze people exhibiting a certain outcome, referred to as the cases, with those not exhibiting the outcome, or the controls, to compare the levels of exposure of an agent in each group. Researchers in case control studies want to determine if an association exists between exposure and a certain outcome.
For example, environmental scientists may research the incidence of respiratory disease in residents of a town with a chemical plant. In a case control study, researchers determine how much exposure to the chemicals residents with respiratory disease experience—the cases—compared to residents without respiratory disease—the controls.
The advantages of case control studies are:
The disadvantages of case control studies include:
6. Cross-sectional studies
Cross-sectional studies are designed to determine the incidence of a certain outcome in a specific population at a set point in time. They often use surveys to gather data from participants. Cross-sectional studies are well suited for measuring the prevalence of a disease or other factor and the efficacy of diagnostic tests.
Businesses can also use cross-sectional studies for planning and development. For example, an organization may want to research the need for an onsite childcare facility for employees. The company may send out surveys to all employees to determine who has children five years old or younger. Planning for future employees needs, the company may also commission a survey of the surrounding counties to research how many families have children five or younger.
The advantages of cross-sectional studies include:
The disadvantages of cross-sectional studies are:
What are the 4 types of studies?
What are the 3 types of studies?
What are the five studies?
- Theoretical Research. …
- Applied Research. …
- Exploratory Research. …
- Descriptive Research. …
- Explanatory Research. …
- Qualitative Research. …
- Quantitative Research. …
- Experimental Research.