What is a Longitudinal Study?

Share this post:

Survey projects can fall into one of two main categories: longitudinal and cross-sectional.

Each one has its strengths and weaknesses, and which category is right for you will depend on what kind of data you are collecting and what kind of insights you need to glean from the results.

Let’s take a look at longitudinal and cross-sectional studies and when they work best for business.

What is the Definition of a Longitudinal Study?

A longitudinal study occurs over many touch points across an extended period of time. They are usually observational in nature. By observational, we mean that the survey makers are not interfering with the subjects or survey respondents.

The most important distinction between longitudinal and cross-sectional studies, for our purposes, is the timeline. Instead of collecting data from different subjects to study the same variables, the researcher surveys the same subjects multiple times, sometimes over many year.

Many medical studies are longitudinal, following the same 100 individuals over the course of years.  A longitudinal study with the same subjects allows researchers to measure changes over time.

While popular for the medical and scientific communities, longitudinal studies can have big benefits for business.

With them, you can track and measure topics as varied as:

  • Market trends
  • Brand awareness
  • Product feedback
  • Customer satisfaction
  • Employee engagement
  • and much more

The Three Kinds of Longitudinal Studies

There are three distinct kinds of longitudinal studies. They are:

  • Panel
  • Cohort
  • Retrospective

A panel study will involve a representative sample of subjects, usually found through a panel services company.

In contrast, a cohort study observes subjects that fall in a similar group or demographic based on shared characteristics. This could include region, age, or common experience.

A retroactive study takes advantage of historical data, often times in comparison to updated data.

What is a Cross-Sectional Study?

A cross-sectional study, closely related to longitudinal studies, aims to compare multiple population groups at a single point in time. Instead of tracking a single variable over time, the researcher frames a cross-section to observe differences among population subsets across several categories.

An example would be a study on the benefits of jogging. In this study, researchers take multiple measurements, such as resting heart rate, body mass index, and blood pressure, across groups with varying exercise levels.

Researchers aren’t collecting data from a single subject over several years to learn about the effects of jogging, but from many subjects just once. This is often referred to as a ‘snapshot.’

Longitudinal and Cross-Sectional Studies: Advantages and Disadvantages

The key advantage to longitudinal studies is the ability to show the patterns of a variable over time. This is one powerful way in which we come to learn about cause-and-effect relationships. The scope of the study may allow longitudinal observation to reveal “sleeper effects” or connections between different events over a long period, uncovering links that might otherwise go unnoticed.

There are, of course, drawbacks to longitudinal studies, panel attrition being one of them. If you are dependent on the same group of 2,000 subjects for a study that takes place once every year, for twenty years, obviously some of those subjects will no longer be able to participate, either due to death, refusal, or even changes in contact information and address. That cuts down on usable data you can draw conclusions from.

Another weakness is that researchers pre-determine the observation periods for collecting longitudinal data, which prevents them from accounting for events occurring between those points. A third disadvantage is panel conditioning, where respondents may unknowingly adjust their qualitative responses over time to align with what they perceive as the researcher’s intended goal. The process of the study itself has changed how the subject or respondent views the questions.

Cross-sectional studies aren’t perfect either. Their single-survey nature makes them unsuitable for drawing conclusive observations about the direction of any given association between variables. However, the benefits could outweigh the narrow scope disadvantages for many businesses.

For one, cross-sectional studies are affordable when compared to a similar longitudinal study. With fewer touch points (no follow up), they are also much quicker in reaching an observational conclusion. Also, provided the sample size is carefully chosen, cross-sectional studies can be helpful in representing entire populations, rather than subsets. This can be very beneficial when considering policy changes.

Logintudinal Studies vs. Cross Sectional: Which is better?

Neither, really. It all depends on what you need for your business.

The idea behind both longitudinal and cross-sectional studies is, again, to create the best process in order to collect the most useful and actionable data. One is certainly not better than the other. They both serve a very important purpose, in different ways.

The number of variables you want to study, the time available before you need published results, your budget, and, perhaps most importantly, the nature of the event you are studying may all influence your choice.

Ready to get started with your own study? Start a trial at Alchemer.

Get Your Free Demo Today
See How Easy Alchemer Is to Use
Start making smarter decisions
Related Posts