Longitudinal Study Là Gì


In a longitudinal study, researchers repeatedly examine the same individuals lớn detect any changes that might occur over a period of time.

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Longitudinal studies are a type of correlational research in which researchers observe và collect data on a number of variables without trying khổng lồ influence those variables.

While they are most commonly used in medicine, economics, và epidemiology, longitudinal studies can also be found in the other social or medical sciences.

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How long is a longitudinal study?

No mix amount of time is required for a longitudinal study, so long as the participants are repeatedly observed. They can range from as short as a few weeks to lớn as long as several decades. However, they usually last at least a year, oftentimes several.

One of the longest longitudinal studies, the Harvard Study of Adult Development, has been collecting data on the physical & mental health of a group of Boston men for over 80 years!

Longitudinal vs cross-sectional studies

The opposite of a longitudinal study is a cross-sectional study. While longitudinal studies repeatedly observe the same participants over a period of time, cross-sectional studies examine different samples (or a “cross-section”) of the population at one point in time. They can be used to provide a snapshot of a group or society at a specific moment.


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How to lớn perform a longitudinal study

If you want khổng lồ implement a longitudinal study, you have two choices: collecting your own data or using data already gathered by somebody else.

Using data from other sources

Many governments or research centers carry out longitudinal studies & make the data freely available khổng lồ the general public. For example, anyone can access data from the 1970 British Cohort Study, which has followed the lives of 17,000 Brits since their births in a single week in 1970, through the UK Data Service website.

These statistics are generally very trustworthy và allow you lớn investigate changes over a long period of time. However, they are more restrictive than data you collect yourself. Lớn preserve the anonymity of the participants, the data collected is often aggregated so that it can only be analyzed on a regional level. You will also be restricted khổng lồ whichever variables the original researchers decided khổng lồ investigate.

If you choose lớn go this route, you should carefully examine the source of the dataset as well as what data is available lớn you.

Collecting your own data

If you choose khổng lồ collect your own data, the way you go about it will be determined by the type of longitudinal study you choose khổng lồ perform. You can choose to lớn conduct a retrospective or a prospective study.

In a retrospective study, you collect data on events that have already happened.In a prospective study, you choose a group of subjects and follow them over time, collecting data in real time.

Retrospective studies are generally less expensive and take less time than prospective studies, but are more prone to lớn measurement error.

Retrospective vs prospective exampleIn a retrospective study, you might look at past medical records of patients to lớn see whether those who developed this cancer had previously smoked. In a prospective study, you might follow a group of both smokers and non-smokers over time to see if they develop cancer later on.

Advantages và disadvantages of longitudinal studies

Like any other research design, longitudinal studies have their tradeoffs: they provide a chất lượng set of benefits, but also come with some downsides.


Longitudinal studies allow researchers to follow their subjects in real time. This means you can better establish the real sequence of events, allowing you insight into cause-and-effect relationships.

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ExampleA cross-sectional study on the impact of police on crime might find that more police are associated with greater crime and wrongly conclude that police cause crime when it is the other way around. However, a longitudinal study would be able lớn observe the rise or fall in crime some time after increasing the number of police in an area.

Longitudinal studies also allow repeated observations of the same individual over time. This means any changes in the outcome variable cannot be attributed to lớn differences between individuals.

ExampleYou decide to study how a particular weight-training program affects athletic performance. If you choose a longitudinal study, the impact of natural talent on performance should be eliminated, since that would not change over the study period.

Prospective longitudinal studies eliminate the risk of recall bias, or the inability to correctly recall past events.

ExampleYou are studying the effect of low-carb diets on weight loss. If you asked your subjects to lớn remember how many carbs or how much they weighed at any point in time in the past, they might have difficulty doing so. In a longitudinal study, you can keep track of these variables in real time.


Longitudinal studies are time-consuming & often more expensive than other types of studies, so they require significant commitment & resources lớn be effective.

Since longitudinal studies repeatedly observe subjects over a period of time, any potential insights from the study can take a while to be discovered.

ExampleIn the study examining the link between smoking & stomach cancer, you have to wait several years to lớn see any results since the negative effects of smoking accumulate over decades.

Attrition, which occurs when participants drop out of a study, is common in longitudinal studies & may result in invalid conclusions.

ExampleIn your study on the impact of low-carb diets on weight loss, participants who are not seeing much success might feel more discouraged and thus more likely to drop out. The diet might therefore appear khổng lồ be more successful than it actually is!

Frequently asked questions about longitudinal studies

Longitudinal studies và cross-sectional studies are two different types of research design. In a cross-sectional study you collect data from a population at a specific point in time; in a longitudinal study you repeatedly collect data from the same sample over an extended period of time.

Longitudinal studyCross-sectional study
Repeated observationsObservations at a single point in time
Observes the same group multiple timesObserves different groups (a “cross-section”) in the population
Follows changes in participants over timeProvides snapshot of society at a given point

Longitudinal studies can last anywhere from weeks lớn decades, although they tend khổng lồ be at least a year long.

Longitudinal studies are better khổng lồ establish the correct sequence of events, identify changes over time, và provide insight into cause-and-effect relationships, but they also tend to be more expensive and time-consuming than other types of studies.

The 1970 British Cohort Study, which has collected data on the lives of 17,000 Brits since their births in 1970, is one well-known example of a longitudinal study.

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