Epidemiological Studies: A Beginners guide

This video gives a simple overview of the most common types of epidemiological studies, their advantages and disadvantages. These include ecological, case-series, case control, cohort and interventional studies. It also looks at systematic reviews and meta-analysis.

This video was created by Ranil Appuhamy
Voiceover - James Clark

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Disclaimer:
These videos are provided for educational purposes only. Users should not rely solely on the information contained within these videos and is not intended to be a substitute for advice from other relevant sources. The author/s do not warrant or represent that the information contained in the videos are accurate, current or complete and do not accept any legal liability or responsibility for any loss, damages, costs or expenses incurred by the use of, or reliance on, or interpretation of, the information contained in the videos.

[krishansinghSMX]

Exam notes:

1. Process of epidemiological studies:
Study question --> select a study type --> collect and analyse data --> interpret result --> report finding. Finally, it should be done in an ethical way

2. Ecological study: applies to groups and not individuals.
- Useful for comparing health across multiple places (e.g., measles rate across Australia and New Zealand), or comparing two time periods in a single place.

- Generating questions that can lend themselves to future investigation and studies.

3. Case series:
- Characteristics of a group of people with same disease or same exposure. The aim is to understand demographics, presentation, prognosis or other characteristics of people who have a particular disease.

4. Cross sectional study:
-It takes a selected population and measure health information at a given point of time, giving a snapshot of health. E.g., using surveys. They are also called prevalence study. Selected population should be representative of the total population.

Advantages:
- Relatively inexpensive
- Assessing exposure/outcomes
- Assess health needs

Disadvantages:
- Cannot be used to measure causality

5. Case control:
- Starts with cases, people with diseases. Uses a control group, similar people but no disease. Both groups are asked about their exposure to certain risk factors, and then odds ratio is calculated as given below:

OR = odds of being exposed – case/odds of being exposed – control

If OR>1, risk factor is associated with the disease
If OR=1, risk factor is not associated with the disease
If OR<1, risk factor is a protective factor

Commonly used for food-borne outbreak investigation.

Advantage:
- Quick and cheap
- Good for uncommon/rare diseases

Disadvantages:
- Uses small numbers so not good for rare exposures
- Finding suitably matched controls
- Recall maybe a problem

6. Cohort studies:

A group of people is followed over a period to see what happens to them, and information about risk factor is collected. Compare the occurrence of outcome in those exposed to those not exposed. Main measurement is relative risk.

Relative risk = risk of disease in the exposed group/risk of disease in the un-exposed group

RR>1, increased risk
RR=1, same risk
RR<1, lower risk

E.g., British doctor’s study conducted in 1950’s. A group of doctors were followed up for many years Valuabe scientific evidence about harmful effects of smoking, especially relation between smoking and lung cancer.

Advantages:
- Time sequence (causality) can be determined
- several different outcome and risk factors can be collected at the same time
- Allows sub analysis

Disadvantages:
- It can be very expensive
- Not good for rare disease
- Ensuring people who started the study stay till the end

7. Interventional study:

An intervention is done on a group of people and outcome measured. For e.g., giving medicine, vaccine or advice. Outcome is change in disease status or behaviour.

Randomised Controlled Trial (RCT) is the best intervention study design. The study populaiton is randomly divided into two groups: intervention group that is given the drug (being tested), and the control group that is not given the drug, instead they are given a placebo.

The outcome is measured in two groups. Outcome could be change in disease, symptoms or death rate.

Advantages:
- Good evidence of causality
- Randomisation helps negate the effect of confounding variables

Disadvantages:
- Expensive
- Needs many participants
- Not always possible where not giving drug could be unethical

8. Systematic review identifies all the relevant studies on a given topic. Assesses, synthesizes, interprets the findings and finally present an impartial, unbiased, and balanced summary of the evidence.

9. Meta analysis uses data form all the studies that consider the same question and use the same study design. Uses data from these studies to combine statistical analysis and produces a single summary result.

[Biomeducated]

Summary notes of study types:
1. 1:09 Ecological Study: comparing health of groups in different places or at different times
2. 1:52 Case Series: describe characteristics (demographics, clinical presentation, prognosis, unusual observations) of a group who has same disease or exposure.
3. 2:19 Cross-Sectional Study: snap shot at a given time on health in a group (e.g. health surveys) (also called prevalence studies)
4. 3:16 Case-Control Study: establish chance of exposure to a risk factor in cases (e.g. patients) vs controls (healthy individuals) over time (odds-ratio calculation)
5. 4:54 Cohort Study: follow group over time and check risk factors along the way (relative risk calculation)
6. 6:52 Interventional Study: double/triple-blinded randomized-control trials (e.g. test effects of a new drug)

Overview studies of multiple studies:
8:52 Systematic review
9:08 Meta-analysis

Study types 1, 2, 3 are ‘snapshots’ at a single point in time, while Study types 4, 5, 6 are ‘longitudinal’, meaning over a longer time period. Study type 4 is mostly retrospective (looking at the past), while Study type 5 and 6 are prospective (looking at the future).
Study type 4, 5, 6 can determine or describe probability of causality,
which is not possible in Study types 1, 2, 3.
Study types 1-5 are ‘observational’, while Study type 6 is ‘interventional’.

Watch the full video for examples and listing of advantages and disadvantages!

[tabithamiller]

This video has taught me more in 10 minutes that my epi class taught me in 5 weeks.

[indaapaulus]

The way I'm going to remember this voice while writing my you so much really helpful..Epidemiology exams you can come now for all I care I'm going to Ace you....

[SunshineSmile]

Thank you so much! Although I'm German and not that good in English, I was able to understand the topic much better than with the help of regular German literature on epidemiology.

[prakashadhikari]

These 10 minutes taught me more than i studied for a whole year

[lillycarinabenedikt]

I absolutely love this video. I'm currently in my M.Sc Public Health. I had to learn this so many times but it was so helpful as a refresher. Maybe a little fast :)
Please keep up the good work

[studentxcmu]

Finally, I know the difference between case control and cohort study. Thanks a lot.

[rakeshsahoo]

Superb.... :-)
So simple and nicely presented. As a student, we need these topics to be presented as interesting as this video was. Thank you and keep uploading more of these types of videoes....

[AK-dnpn]

This is the best video I have watched to understand biostats/different studies in a short time, a tremendous thank you to the makers!

[noofkhalifa]

woowww!!! this video is amazing!!! i was in the university, listening to my instructor for about 1hour and 20min and I did not understand anything, but now I get everything!!! thank you so much

[harishsathish]

Thank you so much! It helped me study for my Disease Detectives Science Olympiad Test. Very helpful information.

[zamiraakbarova]

I learn from you which I could not from my teachers for the three months. Thank you so much for your hard work and good explanation!

[moviemaker]

I love how you chose to animate/play out your voice over with the graphics! I saw this video in class when I was initially learning the various studies and it helped me a lot!

[mpayero]

Excellent video. Today, I read 3 chapter based on that information. I finally assimilated the info because of the help of this video.

[unknownperson-ptbf]

You don’t know how this video ease me , it’s like a cold water in a hottest day, thank you 🌺🌺

[yasemingocmen]

thank you! it’s 2am and i’m still studying and you helped me by putting all that information into one video which was kind of fun to watch! could you do more videos of topics like salutogenisis and the process of a study?

[swnerd-]

I’m a current MPH student and this is a very succinct presentation. 😊

[ForTheSoul]

Thank you professor Liwen Zeng at the UofA for providing this link. Executed with me in mind. Intuitive, succinct, and informative.

[HelenBGumba-oouz]

An easy way for my students to understand the different Epid. strategies which supported my teaching material.