This document discusses longitudinal design and its types. A longitudinal study observes the same subjects over an extended period of time to study changes. There are several types of longitudinal designs, including panel studies that follow the same individuals, cohort studies that follow groups based on a shared characteristic, and retrospective studies that examine past records. Longitudinal research can measure outcomes like risk factors, treatment effects, patterns of change and stability, and historical or developmental impacts. Key types are prospective panel studies with single or multiple cohorts, retrospective panel designs, record linkage studies, and repeated cross-sectional trend studies.

1. Longitudinal Design
and its Types
ASSIGNED BY: DR.ZAFAR IQBAL
PRESENTED BY: NAUMAN KHAN (MS-II)

2. Definition:
 A longitudinal study is an observational research method in which data is
gathered for the same subjects repeatedly over a period of time.
Longitudinal research projects can extend over years or even decades.
 In a longitudinal cohort study, the same individuals are observed over the
study period. Cohort studies are common in medicine, psychology and
sociology, where they allow researchers to study changes over time.

3. Longitudinal Design:
 This study type is particularly useful for evaluating the relationship between risk
factors and the development of disease, and the outcomes of treatments over
different lengths of time.
 Similarly, because data is collected for given individuals within a predefined group,
appropriate statistical testing may be employed to analyze change over time for
the group as a whole, or for particular individuals

4. Longitudinal Design:
 A few key things to remember about longitudinal studies:
 They are observational in nature
 They are a type of correlational research
 Longitudinal research is often contrasted with cross-sectional research
 Longitudinal research involves collecting data over an extended period, often years
or even decades
 Cross-sectional research involves collecting data at a single point in time

5. Dimensions of Longitudinal Design:
 Settings:
Applied in ranging from Highly controlled laboratory to large scale national
surveys.
 Time Scale:
Can be measured from very short period of time to many years.

6. Dimensions of Longitudinal Design:
 Number of Time points:
Varies in terms of How many times information is collected from the same set
of people in panel study or different set of people in trend study.
[Trend Study: (Repeated Cross-sectional Study), entail collecting information from
comparable samples overtime but not from the same people].
[Panel Study: it involves repeated surveys of the same people. It involve collecting
data concerning at least two times points.
Planned Interventions: Vary from planned interventions to naturally occurring
events.

7. Purpose of Longitudinal Design:
 Describing Patterns of Change and stability.
 Establishing Temporal Order.
 Establishing developmental (Age) Effect.
 Establishing Historical (Period) Effect.
 Life Course “Career” analysis.

8. Types of Longitudinal Design:
 Panel Study: Involves sampling a cross-section of individuals.
 Cohort Study: Involves selecting a group based on a specific event such as birth,
geographic location or historical experience.
 Retrospective Study: Involves looking to the past by looking at historical
information such as medical records.

9. Types of Longitudinal Design:
 Prospective Panel Design:
“Prospective studies where the same participants are followed over a period of time”.
1. Simple Prospective Panel Design:- (requires the collection of data at two points
of time from same sample).
2. Multiple Point Prospective Panel Design:- (similar to simple prospective but
involves more data collection points).
3. Single Panel Design without replacement:- (the more points at which the data
are collected and the longer the data of the study, the more dropouts become a
problem). (Two problems: 1. Unacceptably small final sample, 2. Final sample can
become unrepresentative which threatens external validity).

10. Types of Longitudinal Design:
 Prospective Panel Design:
“Prospective studies where the same participants are followed over a period of time”.
4. Single Panel Design with replacement:- (the more points at which the data are
collected and the longer the data of the study, the replacement for sample dropouts
to include new types of members to the sample). (sample size and representativeness
is maintained).
5. Rotating Panel Design:- (systematic and randomized way of dealing with sample
dropout and in so doing maximizes the external validity). (Frequently measure).

11. Types of Longitudinal Design:
 Prospective Panel Design:
“Prospective studies where the same participants are followed over a period of time”.
4. Single Cohort Design:- (involve selecting a group of similarly aged people at one
point of time and following it over an extended period).
5. Multiple Cohort Design:- (Its main feature is the spread of cohorts. This spread
permits comparisons between cohorts and thus helps distinguish between ageing
and period effects).
6. Cohort Sequential Design:- (Its distinctive aspect is that over time cohorts drop
out of the study).

12. Types of Longitudinal Design:
 Retrospective Design:
“Involves looking to the past by looking at historical information such as medical
records”.
1. Retrospective Panel Design:- (it enables us to establish the sequence of events,
which, in turn, enables us to make stronger assertions about causal order and
causation).
2. Record Linkage Design:- (It’s a design where data are collected from official
records. Where these records have been collected overtime).
3. Quasi-Longitudinal Design:- (It entails collecting data at different points of time
so that changes can be plotted, but these data are collected from different individuals
at each time point).

13. Types of Longitudinal Design:
 Retrospective Design:
“Involves looking to the past by looking at historical information such as medical
records”.
4. Simulated Before-After Design:- (entail measuring a group before and after an
intervention and again afterward and hence the impact of intervention is estimated).
5. Repeated cross-sectional Design:- (It’s obtaining the data over time that allows us
to track the change at aggregate level).

14. Thank You!