Study Designs Dr. Abdulmohsen Alzalabani MBChB, ABCM, MSc(Epi), MHPE Assistant Professor, Community Medicine Chairman, Medical Education Department College of Medicine, Taibah University
Research? the process of answering a question by appropriately collected data What is the frequency of a disease in a certain place at a certain time? What caused this disease? Descriptive Hypothesis generation Hypothesis testing the process of developing a list of possible candidates for the “causes”
Is anise effective in prevention of Influenza?
هل اليانسون مفيد للوقاية من الانفلونزا؟
Define your question
Relief of symptoms?
Prevention of infection?
Prevention of disease?
Prevention of complications?
Exposure/Intervention and Outcome Intervention Exposure Anise Mobile phones Outcome Outcome Influenza Brain Cancer
So, how to answer the question?
Mr. Ali is a 50 years old taxi driver in Riyadh. ……………… .. ……………… .. ……………… .. He reported that he drink a cup of Anise everyday. He claimed he never caught flu since he started drinking Anise. Case-report Problems? Anecdotal evidence
A group of people aging between 40 and 50 years working as taxi drivers in Riyadh. ……………… .. ……………… .. ……………… .. They reported that they drink a cup of Anise everyday. They claimed they never caught flu since they started drinking Anise. Case-series Problems? Anecdotal evidence
Population Random Sample Drinking Anise Not drinking Anise Cross-sectional Study (Survey) All measured at the same time Influenza No Influenza
Cross-sectional studies (surveys)
are the simplest type of epidemiological study
information is collected from each subject at one point in time
information can be on outcomes (e.g. diseases, infections, high blood pressure, low birthweight)
information can be on exposures (e.g. smoking, diet, occupation)
information can be on both outcomes and exposures (e.g. HIV positivity and injecting-drug use).
EXAMPLE : Survey of current headache With headache No headache Total Students in this class
EXAMPLE : Survey of current headache With headache No headache Total Students in this class 5 45 50 Prevalence = 5 50 = 0.10 or 10%
Population People without Flu Drinking Anise Not drinking Anise Influenza No Influenza Influenza No Influenza Follow-up Cohort Study
Population People without disease Exposed Unexposed Disease No disease Disease No disease Follow-up Cohort Study
Population Influenza patients People with no Influenza Anise drinker No Anise Anise drinker No Anise Case-Control Study Ask about the past
Population Cases (disease) Control (No disease) Exposed Not Exposed Exposed Not Exposed Case-Control Study Ask about the past
What was the role of the researcher? Observing only Observational Studies Case-control Cohort Cross-sectional Case-series Cross-sectional Case-report Descriptive Studies Analytic Studies Prevalence Distribution Description Testing Association Difference
Experimental studies Normal people Give “Anise” Influenza No Influenza Before-after Problems? Follow-up
Experimental studies Normal people Give “Anise” Influenza No Influenza Controlled Trial Problems? Normal people Give “Nothing” Influenza No Influenza Follow-up
Experimental studies Normal people Give “Anise” Influenza No Influenza Randomized Controlled Trial (RCT) Problems? Normal people Give “Nothing” Influenza No Influenza Normal people randomize Follow-up
How do you go about designing a study?
Decide which is the outcome and which is the (primary) exposure
Is the outcome rare?
Is the exposure rare?
Any existing, useful, databases?
General concerns with all types of studies
Clear definitions of exposure and outcome
Use valid/reliable methods
Non-response can introduce bias
The primary concern in the design of any study must be validity