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What is a Longitudinal Study? Definition, Types & Examples

Kate William

7 min read

Sonia was conflicted. A few months ago, a survey from a grocery delivery app had asked her if she preferred normal eggs or the free-range ones.

She was financially stressed and couldn’t afford to pay more for free-range eggs, so she picked the normal ones.

But last night, she had watched a popular documentary on Netflix about how hens were treated in cages, and now felt much more strongly about wanting to buy free-range eggs.

There was no way for Sonia to communicate this new preference to her grocery delivery app.

But that’s the thing about consumer trends. They are constantly shifting, and one survey taken years ago is not going to give you an accurate picture of the shifts in trends.

That’s why your business needs to understand what is a longitudinal study.

At times, a one-off survey simply isn’t enough to give you the data you need. If you need to observe certain trends, behaviors, or preferences over time, you can use a longitudinal study.

At Surveysparrow, we have just the right survey templates to help you with longitudinal studies. But for now, let’s try to understand what is a longitudinal study.

What is a Longitudinal Study?

The simplest way to understand what is a longitudinal study is to think of it as a survey taken over time. The passing of time could influence the responses of the same person to the exact same question. Like with Sonia, her preferences for eggs changed since she watched the documentary. That’s the kind of thing that longitudinal research design measures.

As for a formal definition, a longitudinal study is a research method that involves repeated observations of the same variable (eg. a set of people) over a period of time. The observations over a period of time might be undertaken in the form of an online survey. It can be tremendously useful in a variety of fields to be able to observe behavior or trends over a period of time.

The applications of knowing what is longitudinal studies are plenty. Longitudinal studies are used in fields like clinical psychology to measure a patient’s thoughts over time, or in market research to observe consumer trends. They are also helpful in political polling and sociology, observing life events and societal shifts over time. Longitudinal research design is also used in medicine to discover predictors of certain diseases.

Types of Longitudinal Studies

When talking about what is a longitudinal study, we cannot go without also discussing the types of longitudinal research design. There are different studies based on your needs. When you understand all three types of longitudinal studies, you’ll be able to pick out the one that’s best suited to your needs.

Panel Study

When we want to find out trends in a larger population, we often use a sample size to survey. A panel study is simply observing that sample size over time. By doing so, panel studies can identify cultural shifts and new trends in a larger population.

Panel studies are designed for the purposes of quantitative analysis. Through the data from online surveys, you can identify common patterns in the responses from your sample (which remains the same over time). With Surveysparrow’s results dashboard, we make it easier for you to conduct such analysis of your collected data.

In panel studies, it is crucial that the same set of people be studied over time. If you pick a different sample, variations in individual preferences could skew your results. Observing the same set of people can make sure that what you’re observing is a change over time.

Cohort Study

A longitudinal cohort study is one in which we study people who share a single characteristic over a period of time. Cohort studies are regularly conducted by medical researchers to ascertain the effects of a new drug or the symptoms of a disease.

In cohort studies, the behaviors of the selected group of people are observed over time to find patterns and trends. Often, these studies can go on for years. They can also be particularly useful for ascertaining consumer trends if you’re trying to research consumers with a specific common characteristic. An example of such a study would be observing the choice of cereal for kids who go to Sunshine Elementary School over time.

If you’re confused between panel studies and cohort studies, don’t worry. The one key difference between cohort studies and panel studies is that the same set of people have to be observed in the latter. In cohort studies, you can pick a different sample of the same demographic to study over time.

Retrospective Study

A retrospective longitudinal study is when you take pre-existing data from previous online surveys and other research. The objective here is to put your results in a larger timeline and observe the variation in results over time. What makes retrospective studies longitudinal is simply the fact that they’re aimed at revealing trends over time.

When understanding what is a longitudinal study, it’ll be well worth your while to look into retrospective studies. For your company, retrospective longitudinal studies can reveal crucial insights without you having to spend a single dime. Since these studies depend on existing data, they not only don’t cost much themselves but also improve the returns from your earlier research efforts.

How can retrospective longitudinal studies be useful to you? Let’s assume for example that you conduct an employee engagement survey every year. If your organization has done these surveys for the past 10 years, you now have more than enough material to conduct a retrospective study. You can then find out how employee engagement at your company has varied over time.

Pros and Cons of Longitudinal Research Design

Like with every research method, longitudinal studies have their advantages and disadvantages. While trying to understand what is a longitudinal study, it is important to get the particular ways in which they’re useful, and situations in which they’re not.  Let’s go over some of the major pros and cons of longitudinal surveys.

Advantages of Longitudinal Studies

  1. Rigorous Insights: A one-off online survey, no matter how well designed, is only so rigorous. Even though the results are often useful, sometimes you need more rigor in your surveys. A longitudinal survey, by observing respondents over time, can offer more rigorous results.
  2. Long-term Data: When thinking about what is a longitudinal study, it is crucial to understand that it is best used for a specific type of data collection. When you need to understand trends over the longer term, longitudinal studies are best suited to that task.
  3. Discover Trends: Most companies, in one way or another, rely on trends they estimate will be relevant in the future. Longitudinal studies can be great at finding out those trends and capitalizing on them before the competition.
  4. Open To Surprises: When designing an online survey, it is very tough to allow for surprises. Mostly, you get what you ask for. With longitudinal surveys, you’re allowing for the possibility that you might spot patterns you didn’t imagine could exist. Longitudinal studies are more flexible in that regard, and allow us to discover the unexpected.

Disadvantages of Longitudinal Studies

  1. Higher Costs: Because longitudinal research needs to be conducted over time, and in some cases with the same set of people, they end up being costlier than one-off surveys. From conducting the observations to analyzing the data, it can add up financially. Using a cost-effective online survey tool like Surveysparrow can be one way to reduce costs.
  2. More Demanding: One of the biggest challenges you can face while conducting a survey is to get enough respondents. Even for normal online surveys, it can be tough to get people to take your survey. Longitudinal surveys are far more demanding, so it is unlikely that anyone will participate without strong incentives.
  3. Unpredictability: While unpredictability can sometimes be a good thing, at times it can also lead the whole exercise astray. The success of a longitudinal study depends not just on the resources you invest in it, but also on the respondents who have to participate in a long-term commitment. Things can go wrong when respondents are suddenly unavailable. That’s why there’s always an element of unpredictability with longitudinal surveys.
  4. Time-Consuming: Unlike simple online surveys, you don’t get the results instantly with longitudinal surveys. They require a certain vision, and you have to be patient enough to see it through to get your desired results.

Examples of Longitudinal Surveys

Longitudinal surveys have been used by researchers and businesses for a long time now, so there is no dearth of examples. Let’s walk through a few of them so you can better understand what is a longitudinal survey.

Australia’s ‘45 and Up’ Survey

There is no better example to understand what is longitudinal research than the 45 and Up study being conducted in Australia. It aims to understand healthy aging, and has 250,000 participants who are aged 45 or older. The idea is to get a better idea of the health of Australians as they get older.

Such a study needed to be a longitudinal survey since you can only understand the effects of aging en masse by considering the results over time. The results from this study are being used in areas like cardiovascular research and preventable hospitalizations.

Smoking and Lung Cancer

To understand the effects of smoking, you need to be able to assess its consequences over time. The British Doctors Study, which ran from 1951 to 2001, yielded results that strongly indicated the link between smoking and lung cancer. If not for longitudinal research methods, we might never have known.

Even though the research was first published in 1956, the study went on for almost half a century after that. When thinking about what is a longitudinal study, we must also consider that these studies give results while they’re ongoing. Conclusively proving the link between smoking and cancer required a robust, longitudinal survey.

Growing Up In Ireland

Started in 2006, Growing Up In Ireland is a longitudinal study conducted by the Irish government to understand what the life of children looks like in different age brackets. One cohort that the study started following at 9 years of age is now 23. The long-term study, by following a set of children throughout their childhood, can yield interesting results.

The thing to remember when thinking about what is a longitudinal study is that they can have broad objectives. You can go in without really knowing what you’re trying to find and what that might lead to. You can then use the surprises along the way to generate actionable insights.

Wrapping Up

At Surveysparrow, we love surveys of all kinds. For certain types of questions, you simply need to conduct longitudinal surveys, and we’re here to support you through the process. With our online templates and intuitive UI, conducting a longitudinal survey will be much easier than ever before.

If you started out wondering what is a longitudinal study, we hope that we’ve addressed that question and more in this article. If you want to create a longitudinal survey, don’t forget to first plan out your survey. A retrospective study, like we just talked about, can also be a great solution to your problems.

The thing to love about longitudinal surveys is the surprising results they can yield. That is really what drives us at Surveysparrow, that you might find something in the results that you didn’t expect, and it might change the course of your company for the better. Conduct a longitudinal study today, and get actionable insights that can help you solve your biggest obstacles as a business and accelerate your growth!

Kate William

Content Marketer at SurveySparrow

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