1. TYPES OF STUDIES IN DIABETES EPIDEMIOLOGY
A number of epidemiologic studies are available and have been used for diabetes researches. In this lecture, I will discuss the type of epidemiologic studies that have been used in diabetes research and point out the pros and cons for each study.

2. TYPES OF STUDIES BASED ON:
Purpose
Time
Cost
Feasibility
Before conducting any diabetes research, the researcher must decide on the purpose, the duration, the cost, and finally the feasibility of the study. If the researcher plans to conduct a pilot study, he does not need to design a complex study but rather a simple one that is cheap, easily accessible to the subjects and can be completed in a short period of time. However, if the researchers are looking for a community based study. The research should expect a high cost, a longer research time and poorer feasibility.

3. TYPES OF STUDY Observational Descriptive Analytical Experimental
Cross-sectional
Retrospective
Prospective
Experimental
Clinical Trial
Community Intervention Trial
Field Trial
Epidemiologic studies are divided into the two major areas: observational and experimental. Observational studies are usually called either descriptive or analytical. If one plans to conduct an observational study, one does not have control over the study subjects. The researcher simply observes the outcome and factors associated with the disease. On the other hand, an experimental study has full control over the study subjects. This type of study is usually conducted in a clinical, community intervention, and field trial setting. I will be discussing about each study in the latter part of my lecture.

4. A STUDY DESIGN FOR THE OUTCOMES OF DIABETES
Morbidity (Complications)
Mortality (Death)
Economics
Treatment
Education
Prevention & Control
Intervention
These are the areas in diabetes research where epidemiologic studies are greatly in need. These areas including: Diabetes outcome researches in different type of diabetes. Research on the complications and the mortality. Economic research relates to diabetes care, treatment, diagnosis, and prevention. Research is related to patient education, and finally, research for the intervention and prevention of diabetes. More answers to the question of complication and mortality are still in need and open for answers.

5. TIME AND TYPES OF STUDY PAST PRESENT FUTURE Time Retrospective
Cross-sectional
Prospective
The concept of time is very important in determining the type of epidemiologic study to be done. If you are looking for the relationship of cause and effect during present time, you will need a cross-sectional study. However, if you are looking at the cause and effect relationship of the past, you will need a retrospective study. If you looking at the relationships in the future, you will need a prospective study. I will be lecturing on each one of these studies more in details presenting with the aid of the next few slides.
Time

6. CROSS-SECTIONAL STUDY
PRESENT
Cross-sectional
First, let us look at the cross-sectional study. Cross-sectional studies investigate the association between the putative factors and the disease outcome. In other words, we do not know what happened in the past and what will happen in the future. On the basis of a cross-sectional study, we do not know whether one agent causes the outcome. Thus, a cross-sectional study is only helpful in describing the relationships between the disease and potential causative agents. If one planning a study for first time, a cross-sectional study should be conducted.
Time

7. ANALYTICAL STUDY A cross-sectional study: Privides a snap shot
Is simple
Provides associated factor
Is first line of epidemiologic research
Cross-sectional study is considered an analytical study, because it helps to analyze the relationship between the disease and the potential risk factors. It act like a snap shot and is very simple to conduct in a short period of time. However, it only describes the associated factors of the outcome. Thus, this type of study should only be used as the first line of epidemiologic research.

8. CROSS-SECTIONAL STUDY
What is different about: DM
Morbidity (Complications)
Mortality (Death)
How is it different about:
SES
Age at onset
Season
Cross-sectional studies have been used in describing general and clinical characteristics of different type of diabetes such as Insulin Dependent Diabetes Mellitus, Non Insulin Dependent Diabetes Mellitus and Gestational Diabetes. This method of study has been widely used in describing a patients clinical, demographic, and family history, as well as exercise, diet, habits, life style, and the glucose metabolism of subjects morbidities and mortalities with and without diabetes. It helps to understand the potential risk factors such as socio-economic status, age at onset, seasonal characteristics as well as the pattern of disease.

9. CROSS-SECTIONAL STUDY
Denmark
Pittsburgh, USA
Scotland
Sweden
Finland
Korea
Japan
Kuwait
Israel
England
Canada
Netheland
One of the best results from the cross-sectional study has been the exposition of incidence rates. As shown on this slide that incidence rates of IDDM varied widely. The lowest rate was reported from Korea, and the highest from Finland. These differences are as much as 40 fold between the two countries. Based on this cross-sectional study, we immediately noticed that both genetic and environmental conditions should be regarded as risk factors for IDDM. In these cross-sectional studies, we also note that IDDM incidence is lower in Asia, moderate in North America, and higher in Scandinavian countries.
Incidence /100,000

10. RETROSPECTIVE STUDY Determining differences in: Life style Diet
PRESENT
Disease
Life style
Diet
Reproductive on
Medication
Family Hx
Genetics
The next type of epidemiologic study is the retrospective study. Based on the concept of the past. It is past, because we know the disease conditions of the subjects at the time of beginning of the study. In this type of study, we usually select both a group of diseased and normal healthy subjects, and try to find out what factors potentially cause people to get a disease. Usually, one interviews the subjects with regards to potential risk factors. Though outcomes is prone to a memory bias, retrospective study is cheaper, obtains results in a short period of time, and is the best method for studying rare diseases.
PAST
Time

11. RETROSPECTIVE STUDY: PROS & CONS
Suitable for rare diseases
Inexpensive
Minimal ethical problems
Short study time
Small # of subjects
Subjects need not volunteer
Susceptable to selection & memory bias
Inconsistency: definitions of symptoms or diseases may have been modified over time.
Can not determine incidence
Limitations in data
Relative risk approximation
This slide further indicates the pros and cons for retrospective studies.

12. PROSPECTIVE STUDY DM Risk factors??? Future Retinopathy+ PRESENT
The last analytical type of epidemiologic study in presented on this slide. It is called a prospective study and the goal is looking at the future outcome. In other words, at present time we know an individual’s potential risk factors. Therefore, the goal is to follow subjects who have been exposed and not been exposed to potential risk factors for a given period and observe the outcome of the disease. This type of study is openly used in diabetes research. DCCT and DPT is a few of the prospective diabetes research we have been hearing about for a long time.
Time

13. PROSPECTIVE STUDY: PROS & CONS
Consistent disease definitions & symptoms.
Longer time
Common disease only
Expensive
Ethical concern
A high drop-out rate
Volunteers needed
A large # of subjects needed
The Hawthorne-effect
Less variability to bias
No recall necessary
Incidence determined
Relative risk accurate
This slide presents the pros and cons of the prospective study.

14. TYPES OF STUDIES AND GOALS
CROSS-SECTIONAL
Understand
RETROSPECTIVE
Estimate risk factors
I would like to summarize the three types of studies we have covered in this lecture. The goal of the cross-sectional study is a better understanding of the disease and risk factors that are associated with the disease. The retrospective study is good to get an estimation of the potential risk factors and usually these relationships are confirmed by the prospective studies. Therefore, the retrospective study is less valid than the prospective method. The results from these studies have been utilized for diabetes prevention, control, intervention, education and management.
PROSPECTVE
Validate risk factors
Prevention-Control-Intervention-Education-Management

15. EXPERIMENTAL STUDY Animal Drug trials Human
Another area of the epidemiologic study is the experimental study. Unlike analytical studies, in experimental studies, the research has control over the study subject’s activity. These type of studies are usually applied in animals, drug trial and human subjects.

16. EXPERIMENTAL STUDY Exercise Diet Drug Randomized Clinical Trial:DPP
Random Selection
Outcome evaluation
Diet
One of the best experimental studies is the diabetes prevention program which started two years ago. In this experimental study, the subjects were randomly selected from a community and divided to do one of the three trials, ie., exercise, diet or medication. Those high risk subjects assigned to each of the regiment were ask to followed the researcher instruction and the outcome was measured after the study period. The limitations of this time study was the high drop out rates, the high experimental cost, and the question of ethics.
Drug

17. EXPERIMENTAL STUDY Cross-over design Outcome evaluation
In the experimental study, the cross-over design is often used and it is a very powerful tool. The cross-over study design is usually used in drug trials. It is very effective if you do not have a large study cohort or participants must be on medication all the time. Since individuals are serving themselves as a control, you do not need to find additional control subjects. However, the research should have a clear knowledge about the washout period of the medication in trial. If the washout period is not properly applied, the second medication will have a false and an efficacy. This slide presents the single crossover design. Double, triple designs are also available.