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An introduction to different types of study design

Posted on 6th April 2021 by

Tutorials and Fundamentals

Study designs are the set of methods and procedures used to collect and analyze data in a study.

Broadly speaking, there are 2 types of study designs: descriptive studies and analytical studies.

Descriptive studies

  • Describes specific characteristics in a population of interest
  • The most common forms are case reports and case series
  • In a case report, we discuss our experience with the patient’s symptoms, signs, diagnosis, and treatment
  • In a case series, several patients with similar experiences are grouped.

Analytical Studies

Analytical studies are of 2 types: observational and experimental.

Observational studies are studies that we conduct without any intervention or experiment. In those studies, we purely observe the outcomes.  On the other hand, in experimental studies, we conduct experiments and interventions.

Observational studies

Observational studies include many subtypes. Below, I will discuss the most common designs.

Cross-sectional study:

  • This design is transverse where we take a specific sample at a specific time without any follow-up
  • It allows us to calculate the frequency of disease (prevalence) or the frequency of a risk factor
  • This design is easy to conduct
  • For example – if we want to know the prevalence of migraine in a population, we can conduct a cross-sectional study whereby we take a sample from the population and calculate the number of patients with migraine headaches.

Cohort study:

  • We conduct this study by comparing two samples from the population: one sample with a risk factor while the other lacks this risk factor
  • It shows us the risk of developing the disease in individuals with the risk factor compared to those without the risk factor (RR = relative risk)
  • We may approach this study by 2 longitudinal designs:
      • Prospective: we follow the individuals in the future to know who will develop the disease
      • Retrospective: we look to the past to know who developed the disease (e.g. using medical records)
  • This design is the strongest among the observational studies
  • For example – to find out the relative risk of developing chronic obstructive pulmonary disease (COPD) among smokers, we take a sample including smokers and non-smokers. Then, we calculate the number of individuals with COPD among both.

Case-Control Study:

  • We conduct this study by comparing 2 groups: one group with the disease (cases) and another group without the disease (controls)
  • This design is always retrospective
  •  We aim to find out the odds of having a risk factor or an exposure if an individual has a specific disease (Odds ratio)
  •  Relatively easy to conduct
  • For example – we want to study the odds of being a smoker among hypertensive patients compared to normotensive ones. To do so, we choose a group of patients diagnosed with hypertension and another group that serves as the control (normal blood pressure). Then we study their smoking history to find out if there is a correlation.

Experimental Studies

  • Also known as interventional studies
  • Can involve animals and humans
  • Pre-clinical trials involve animals
  • Clinical trials are experimental studies involving humans
  • In clinical trials, we study the effect of an intervention compared to another intervention or placebo. As an example, I have listed the four phases of a drug trial:

I:  We aim to assess the safety of the drug (is it safe ?)

II: We aim to assess the efficacy of the drug (does it work ?)

III: We want to know if this drug is better than the old treatment (is it better ?)

IV: We follow-up to detect long-term side effects (can it stay in the market ?)

  • In randomized controlled trials, one group of participants receives the control, while the other receives the tested drug/intervention. Those studies are the best way to evaluate the efficacy of a treatment.

Finally, the figure below will help you with your understanding of different types of study designs.

A visual diagram describing the following. Two types of epidemiological studies are descriptive and analytical. Types of descriptive studies are case reports, case series, descriptive surveys. Types of analytical studies are observational or experimental. Observational studies can be cross-sectional, case-control or cohort studies. Types of experimental studies can be lab trials or field trials.


References (pdf)

You may also be interested in the following blogs for further reading:

An introduction to randomized controlled trials

Case-control and cohort studies: a brief overview

Cohort studies: prospective and retrospective designs

Prevalence vs Incidence: what is the difference?


Hadi Abbas

My name is Hadi Abbas. I'm Australian-Lebanese, and I'm a medical student at the Lebanese University. My interest in evidence-based health care stems from my belief that to be a professional doctor, there is an absolute need for proof to backing up your every day medical journey. Research is the twin soul of clinical experience. I try to follow every chance which makes me closer to my goal; being successful healthcare professional. View more posts from Hadi

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No Comments on An introduction to different types of study design

  • Haileyesus Gebremariam

    you are amazing one!!
    if I get you I’m working with you!
    I’m student from Ethiopian higher education. health sciences student

    18th January 2024 at 1:10 am
    Reply to Haileyesus
  • Prosunto Kumar Das

    Very informative and easy understandable

    26th November 2023 at 5:07 pm
    Reply to Prosunto
  • Yolande Haugabook

    You are my kind of doctor. Do not lose sight of your objective.

    3rd November 2023 at 6:05 pm
    Reply to Yolande
  • sukanya

    Wow very erll explained and easy to understand

    3rd August 2023 at 9:34 am
    Reply to sukanya
  • khamisu Habibu

    I’m Khamisu Habibu community health officer student from Abubakar Tafawa Balewa university teaching hospital Bauchi, Nigeria, I really appreciate your write up and you have make it clear for the learner. thank you

    24th May 2023 at 12:31 pm
    Reply to khamisu
  • winny

    well understood,thank you so much

    15th May 2023 at 11:31 pm
    Reply to winny
  • Joyce Mganga

    Well understood…thanks

    1st February 2023 at 5:21 pm
    Reply to Joyce
  • Josephine

    Simply explained. Thank You.

    20th October 2022 at 10:38 am
    Reply to Josephine
  • Mona Khalil Elias

    Thanks a lot for this nice informative article which help me to understand different study designs that I felt difficult before

    8th August 2022 at 9:40 pm
    Reply to Mona
    • Emma Carter

      That’s lovely to hear, Mona, thank you for letting the author know how useful this was. If there are any other particular topics you think would be useful to you, and are not already on the website, please do let us know.

      21st September 2022 at 10:53 am
      Reply to Emma
  • john

    Dear sir

    it is very informative and useful.

    thank you

    4th August 2022 at 10:33 am
    Reply to john

    Thanks for this information

    27th July 2022 at 3:46 pm
    Reply to MIREMBE

    Thanks so much for this information….I have clearly known the types of study design

    27th July 2022 at 3:44 pm
    Reply to MIREMBE
    • Emma Carter

      That’s so good to hear, Mirembe, thank you for letting the author know.

      21st September 2022 at 10:54 am
      Reply to Emma
  • Isaac N-eebo

    Very helpful article!!
    U have simplified everything for easy understanding

    14th July 2022 at 8:06 pm
    Reply to Isaac
  • Marcii

    I’m a health science major currently taking statistics for health care workers…this is a challenging class…thanks for the simified feedback.

    1st April 2022 at 7:57 am
    Reply to Marcii
    • Emma Carter

      That’s good to hear this has helped you. Hopefully you will find some of the other blogs useful too. If you see any topics that are missing from the website, please do let us know!

      4th April 2022 at 9:47 am
      Reply to Emma
  • Ay

    Hello. I liked your presentation, the fact that you ranked them clearly is very helpful to understand for people like me who is a novelist researcher. However, I was expecting to read much more about the Experimental studies. So please direct me if you already have or will one day. Thank you

    27th December 2021 at 3:29 am
    Reply to Ay
    • Emma Carter

      Dear Ay. My sincere apologies for not responding to your comment sooner. You may find it useful to filter the blogs by the topic of ‘Study design and research methods’ – here is a link to that filter: https://s4be.cochrane.org/blog/topic/study-design/ This will cover more detail about experimental studies. Or have a look on our library page for further resources there – you’ll find that on the ‘Resources’ drop down from the home page.

      However, if there are specific things you feel you would like to learn about experimental studies, that are missing from the website, it would be great if you could let me know too. Thank you, and best of luck. Emma

      24th February 2022 at 2:50 pm
      Reply to Emma
  • Mohammed AbdulMajeed

    Great job Mr Hadi. I advise you to prepare and study for the Australian Medical Board Exams as soon as you finish your undergrad study in Lebanon. Good luck and hope we can meet sometime in the future. Regards ;)

    9th December 2021 at 11:41 pm
    Reply to Mohammed
  • Martha Daniella Mwaluka

    You have give a good explaination of what am looking for. However, references am not sure of where to get them from.

    8th December 2021 at 1:33 am
    Reply to Martha

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