A prospective cohort study is a research effort that follows groups of people over time who have many similarities, but then they have a specific difference with a singular characteristic. Then the researchers compare the outcomes from within the group to determine if that one characteristic leads to a particular result. The example offered by the National Cancer Institute involves female nurses with those who smoke versus those who do not. Then the data would look at the differences in lung cancer development.
Several advantages and disadvantages of a prospective cohort study are worth reviewing when looking at the ability to gather data points from specific population groups.
List of the Advantages of a Prospective Cohort Study
1. A prospective cohort study provides clarity of the temporal sequence.
A prospective cohort study can more clearly indicate the temporal sequence between an exposure and an outcome. This result is possible because there are definitive behaviors or characteristics available for researchers to observe. The study looks at the entire population and then separates them based on the differences requiring observation. Then work happens to ascertain prior exposures as needed.
This advantage provides a reasonable approach to the establishment of past exposures. It also can use the perspective of each participant to further the information collecting process.
2. It allows for a calculation of incidence.
Researchers that use a prospective cohort study can calculate the incidence of a particular characteristic with ease. This advantage makes it simple to determine what the absolute risk is for the information being studied, the relative risk of the population group, risk differences, and the attributable proportion. Then the outcomes provide generalized information that makes it possible to calculate the potential risk factors for an entire group.
3. The structure of a prospective cohort study facilitates the study of rare exposures.
Although a prospective cohort study is useful in the study of common data points and exposures, it is particularly useful for evaluating the potential impact of an unusual or rare incident. This advantage allows researchers the opportunity to identify an adequate number of participants in the population who may have similar circumstances to see if an external influence is impacting the results.
Researchers used the prospective cohort study approach to measure exposure to Agent Orange in the past. It is useful in the study of adverse drug effects and treatments. Investigators can even use it to look at unusual occupational issues, such as what happens with direct exposure to asbestos.
4. It allows for the examination of multiple effects.
Using the example from the National Cancer Institute, researchers could look at nurses who smoke versus those who do not to look at multiple outcomes. Investigators could compare the amount of exercise that each subsegment receives, total lung capacity between the two groups, or even the number of sick days that get taken.
When researchers looked at what Agent Orange exposure could cause in those who served, the risk factors examined in the prospective cohort study included liver abnormalities, psychological problems, skin disease, and cancer.
5. A prospective cohort study works to prevent selection bias.
The structure of a prospective cohort study naturally works against selection bias by taking a look at an entire population group. Researchers are looking at the comparison of one specific point of reference, such as smoking vs. non-smoking. This advantage is possible because the outcome isn’t known at the baseline when the initial status gets established. You’re only selecting the data points that will get evaluated during the work ahead.
6. It provides a significant recall structure to reduce error rates.
A prospective cohort study creates a recall structure that researchers use to keep track of the population groups. It creates a dual advantage. Investigators can keep track of the data points that develop in real-time so that useful information from the baseline can get reviewed. It also reduces the error rate in the samples because of the long-term nature of this option. Although there will always be some loss because of unexpected events and overlapping outcomes from other developments, this method provides a reliable way to study the impact of behaviors, choices, or exposures.
7. A prospective cohort study uses one population group.
Instead of considering geographic differences or other population limitations, a prospective cohort study looks at the general group. This creates fewer cost differences when compared to other structures because it doesn’t require a lot of initial research to create a baseline. Investigators can look at one specific demographic, and then look at the characteristic differences in that area.
Although the long-term costs may create an imbalance with this advantage for some studies over time, it is a useful method of gathering data on specific areas of life.
8. It allows for data collection from several sources.
Outcome measures from a prospective cohort study can come from a variety of sources. Investigators can use routine surveillance of registry data, death certificates, direct observation, medical records, and anything else that the structure of the work determines is a useful data point. Each method requires additional research at times to determine that the records match the individuals who are participating in this effort.
List of the Disadvantages of a Prospective Cohort Study
1. Follow up bias can occur within a prospective cohort study.
Although investigators don’t know what the outcome will be when they select a data point to research, bias can still occur in a prospective cohort study as a result of differential loss to follow up. When information seems to go in the favor of one group or another in ways that don’t align with the expected result, then investigators can purposely avoid collecting info from one group to make it seem like the outcomes are different.
Using the smoking vs. non-smoking example, researchers could choose data from smokers who didn’t develop lung cancer as a way to compare data from the other group.
2. It requires researchers to follow a large population for a significant amount of time.
When a prospective cohort study gets developed, researchers must choose a large population group to create enough data points to create comparison opportunities. It might also take a lot of time for the results of the comparison to develop, which means investigators typically have more follow up duties with this approach than some of the alternatives that exist. The disadvantage here is that investigators can perform all of this work without a guarantee that a result is going to eventually develop.
When there is such a long follow-up period with a prospective cohort study, then there is also the potential for other diseases or health concerns to develop. These secondary issues can have an adverse impact on the results under investigation.
3. A prospective cohort study is not useful for issues with long latencies.
The nature of human life is unpredictable. You can be following a normal routine when someone blasts through a stop sign and changes your life forever. When researchers follow a large group of people to compare data points on a specific characteristic or trait, then this time factor increases the risk of information loss. When the issue takes a long time to develop, then a prospective cohort study doesn’t provide useful outcomes.
The long latency period may interfere with the accuracy of the data. There is no way to generalize the findings to the general population when this disadvantage occurs.
4. It is not useful for rare situations.
Although the prospective cohort study structure is useful for looking at common situations that population groups face, it is not useful in the study of rare situations. This issue primarily applies to disease, but the disadvantage could apply to any unique situation where a small group of people are different in one way than the rest of the population. There are no guarantees that enough people could be located to provide the foundation for the research.
5. The time and cost of a prospective cohort study may not be manageable.
It takes a significant amount of time for a prospective cohort study to develop results that are useful for comparison purposes. If you were to look at the impact of asbestos exposure using this option, it could be more than 20 years before any useful data would become available. That means researchers would be performing all of their recall efforts at a great cost without any promise of an outcome. That’s why it isn’t a manageable method of investigation for small populations or most rare situations.
6. Differential misclassification can occur with these studies.
One of the significant sources of bias that happens with a prospective cohort study comes from the degree of accuracy with which the classification of participants occurs. When a misclassification occurs, then it can lead to over- or under-estimates of the effect between the exposure and outcome. Although it eliminates selection bias by working with specific demographics, this issue can also further the losses that can happen when there is a lack of follow-up that happens.
7. The prospective cohort study doesn’t handle the healthy worker effect.
The healthy worker effect is a form of selection bias that can sometimes occur when the prospective cohort study approach looks at occupational studies. When disease rates among individuals from a specific occupational group get compared to the external general population, bias can be introduced if members of the exposed cohort are partly dependent upon health. People who have employment are generally healthier because of the nature of what they do. That means the morbidity and mortality rates in an occupational group are often initially lower than those found in the general population.
8. These studies are prone to confounding.
Confounding occurs in a prospective cohort study when the experimental controls do not allow researchers or investigators to reasonably eliminate plausible alternative explanations. This issue creates a misinterpretation of the observed relationships between the dependent and independent values. As a result, many variables become confounded without enough structures in place. That makes it impossible to determine whether a drug or the experiment was effective with its results.
9. Participants in a prospective cohort study can change their classification.
When researchers want to compare nurses who smoke versus those who do not, the initial separation will look at that one specific behavior. Some nurses will decide to stop smoking as a way to promote better health after the work begins, while others may choose to start as a way to cope with the high stress levels that they face with their work. This crossover of behaviors makes it a challenge to determine specific outcomes because of how individuals can choose to change their classification.
This issue can also happen when the classification of individuals through their exposure or outcome status gets affected by changes in the diagnostic procedures.
A prospective cohort study is useful for researchers when they want to look at the etiology of specific diseases or disorders. The distinguishing feature of this approach is that none of the participants have developed any of the outcomes of interest at the time of recruitment, which naturally eliminates the issue of selection bias. Then data gets used to answer the questions about risk factors and subsequent outcomes.
This information makes it easier to determine the risk factors for being infected with a new disease since longitudinal observation occurs over a long time – often several years. Data gets collected during regular time intervals, which minimizes recall error.
Then the prospective cohort study advantages and disadvantages must look at the time and cost investments that are necessary to reach a conclusion. They are more expensive than a case-control study and provide more evidence than a retrospective cohort study, which is why the investment often makes sense.
Blog Post Author Credentials
Louise Gaille is the author of this post. She received her B.A. in Economics from the University of Washington. In addition to being a seasoned writer, Louise has almost a decade of experience in Banking and Finance. If you have any suggestions on how to make this post better, then go here to contact our team.