# Time series vs longitudinal analysis

Are you wondering what the main differences between time series analysis and longitudinal data analysis are? Well then you are in the right place! In this article, we discuss everything you need to know to understand the difference between time series analysis and longitudinal analysis.

First, we describe what time series analysis is and what types of data is used for time series analysis. After that, we describe what longitudinal analysis is and what types of data are used for longitudinal analysis. After that, we discuss some of the main similarities between time series analysis and longitudinal analysis. Finally, we discuss the main differences between time series analysis and longitudinal analysis.

## What is time series analysis?

What is time series analysis? In order to describe what time series analysis is, we will first describe what kind of data time series analysis should be used for. Time series analysis should be used when you have many repeated measurements on a single subject or observational unit. Each of these measurements should be taken using the same methodology, but the different measurements should be taken at different points in time.

All that you need to conduct a time series analysis is an outcome variable that has been observed over time. There is no requirement to have associated features that are measured alongside the outcome variable. This is because time series analysis forecasts future values of the outcome variable using previous values of the outcome variable, rather than modeling future values of the outcome variable based solely on features that are associated with the outcome variable.

Time series analysis often breaks the trends that are seen in data up into multiple different components. One type of component that commonly shows up is a trend component that represents the rate at which the time series is increasing or decreasing over time. Another type of component that commonly shows up is a seasonal component that represents regular seasonal patterns that are seen in the data. There is also an error term that is included to represent random fluctuations in the time series data.

There are two main use cases for time series analysis. The first is when you have historical time series data that you want to decompose into different components. For example, you might want to decompose the time series data into a seasonal component and a trend component. The second situation where time series analysis is useful is when you want to forecast future values of your outcome variable over time.

## What is longitudinal analysis?

What is longitudinal analysis? In order to describe what longitudinal data analysis is, we will first describe what type of data should be used for longitudinal analysis. Longitudinal analysis should be used when you have multiple repeated measurements that are taken on a cohort of subjects or observational units. In this scenario, there should be multiple subjects that are considered and there should be multiple measurements that are taken on each subject.

Unlike time series analysis, when you conduct a longitudinal analysis you generally do need to have measurements on features that are associated with your outcome variable. That is because longitudinal analysis uses the values of the features to predict future values of the outcome variable, rather than using previous values of the outcome variable to predict future values of the outcome variable. Longitudinal models are simply extensions of more simple supervised learning models that can be used in cases where there are multiple observations taken on each subject.

There are many situations where longitudinal analysis is used, but most of these use cases arise when you want to examine the relationship between a specific feature in your model and the outcome variable in your model. Longitudinal analysis is a common choice when you want to evaluate the relationship between the values of your features and the values of your outcome variable over an extended period of time.

## Similarities between time series and longitudinal analysis

What are some of the main similarities between time series analysis and longitudinal analysis? Here are some of the main similarities between time series analysis and longitudinal analysis.

• Repeated measurements on the same subject. The main similarity between time series analysis and longitudinal analysis is that they can both be used in situations where you have repeated measurements that are taken on the same subject. Many other statistical models make the assumption that all of the observations in your dataset are independent, which precludes you from including multiple measurements that were taken on the same subject. Time series models and longitudinal models do not make these assumptions.

## Differences between time series and longitudinal analysis

What are some of the main differences between time series analysis and longitudinal analysis? Here are some of the main differences between time series analysis and longitudinal analysis.

• Time series analysis uses measurements from a single subject. One of the main differences between time series and longitudinal analysis is that time series analysis is meant to be used when all of the repeated measurements you have are taken on a single subject. Longitudinal models, on the other hand, are intended to be used when you have repeated measurements that are taken on multiple different subjects. Looking at the number of subjects that are contained in your dataset is a simple way to determine whether you should use time series analysis or longitudinal analysis.
• Times series analysis does not require covariates. Another difference between time series analysis and longitudinal analysis is that time series analysis does not require the inclusion of features that are associated with the outcome variable. While some time series models can be modified to incorporate feature information, some time series models can not accommodate covariates at all.
• Time series data generally incorporates autoregressive components. Another difference between time series analysis and longitudinal analysis is that time series analysis automatically incorporates autoregressive components that link future values of the outcome variable back to previous values of the outcome variable. While it is technically possible to create longitudinal models that display similar behaviors, these behaviors are not naturally incorporated into the models.
• Time series data is more commonly used for prediction and forecasting. It is very common for time series models to be created with the purpose of forecasting future values of the outcome variable. Longitudinal analysis, however, is more often used to examine historical patterns in your data. While longitudinal analysis technically can be used to forecast future values of a variable, it is less common.