Observational and Experimental Studies
There are two primary ways to collect data from a new sample: an observational study and an experimental study. Both of these methods involve choosing a sample of individuals from the population and recording the value of one or more variables for each individual. However, there are some differences.
In an observational study, no attempt is made to control any aspect of the individuals in the sample. The sample is chosen using an appropriate process, and the variables of interest are recorded for each individual. This kind of study is typically used when it is difficult, unethical, or impossible to control factors in the sample. An observational study is also commonly used when there are no factors that would need to be controlled. Here are a few examples where an observational study would be used:
• A study on the relationship between smoking and the risk of lung cancer • A study on the relationship between premature birth and early reading skills • A survey of the opinions of residents on a proposed addition to the local school
In an experimental study, the researchers attempt to control one or more aspects of the individuals in the sample. The individuals in the sample will be randomly divided into multiple groups or cases. Then the controlled factors will be set for each of the groups as chosen by the researchers. This may be more clear with a few examples of experimental studies:
• Researchers randomly assign individuals to three groups. One group listens to no music, one group listens to a top 40 channel from a streaming service, and one group listens to individually selected music. The researchers then give the subjects a cognitive test. • An agricultural agency divides 100 plots into two groups. One group receives no pesticides and the other group receives pesticide treatments. The crop yields of each plot are measured at the end of the season.
Question
A large manufacturing firm is interested in the effect of the temperature of the manufacturing floor on worker productivity. Over the course of a year, the firm randomly samples its 103 sites and records the temperature and the quantity of items produced on that day. Is this an experiment or an observational study?
A biology student is interested in the relationship between temperature and germination time for soy beans. The student gets sample seeds from multiple sources and randomly selects 180 seeds from them. Then he sets up three growing stations, one at 20°C, one at 15°C, and one at 25°C. He divides the seeds into three groups of 60 and plants the seeds from each group in a growing station. He records the germination time for each seed.
Is this an observational study or an experiment? If it is an experiment, what is the controlled factor?
A biology student is interested in the relationship between temperature and germination time for soy beans. The student gets sample seeds from multiple sources and randomly selects 180 seeds from them. Then he sets up three growing stations, one at 20°C, one at 15°C, and one at 25°C. He divides the seeds into three groups of 60 and plants the seeds from each group in a growing station. He records the germination time for each seed.
Is this an observational study or an experiment? If it is an experiment, what is the controlled factor?
In a study to support drug discovery for patients with lung cancer, patients were divided into 3 groups based on the severity of the disease. Smoking and alcohol consumption habits were recorded for all 3 groups. Is this an example of an observational study or experimental study?