Biostatistics course Part 2 Types of studies in

Biostatistics course Part 2 Types of studies in epidemiology Dr. en C. Nicolas Padilla Raygoza Departrment of Nursing and Obstetrics Division of Health Sciences and Engineering University of Guanajuato Mexico

Biosketch n Medical Doctor by University Autonomous of n n n Guadalajara. Pediatrician by the Mexican Council of Certification on Pediatrics. Postgraduate Diploma on Epidemiology, London School of Hygine and Tropical Medicine, University of London. Master Sciences with aim in Epidemiology, Atlantic International University. Doctorate Sciences with aim in Epidemiology, Atlantic International University. Professor Titular A, Full time, University of Guanajuato. padillawarm@gmail. com raygosan@ugto. mx

Competencies n The reader will differentiate between observational and experimental studies. n The reader will know advantages and disadvantages of both types of studies.

Types of studies Types of epidemiological studies Experimental Observational Randomized Controlled studies Cases or report of cases Cases and controls Cohort Cross sectional Ecologic Quasi. Experimental

Cases in series n Advantages: n They are easy to write. n The observations are useful to other researchers. n Disadvantages: n There a lot of bias.

Cases and controls studies Exposed Cases Non-exposed Exposed Controls Non-exposed Direction of research Beginning of study Time

Cases and controls studies n Advantages: They are adequate to study rare outcomes. n They are adequate to outcomes with long latency period. n They are cheap and easy to apply. n It is not necessary to wait to present outcome. n Disadvantages: n A lot of bias. n They depend on the quality of registries. n Control group should be adequately selected, because they represent the population without the outcome. n

Nested cases and controls studies With outcome Cases Exposed Without outcome Cohort selected to study Sample of controls With outcome Cases Nonexposed Beginning of study Without outcome Sample of controls Time

Cohort studies Exposed Selection of a cohort for study With outcome Without outcome With outcome Non-exposed Beginning of study Without outcome Time

Cohort studies n Subjects are selected because do not have the outcome and they are classified if have or not have the risk factor (exposure). n We follow up to prove if they develop the outcome. n The cohort study can be prospective if the follow up is forward in the time or it can be retrospective (historic), if it go back in the time.

Cohort studies n Advantages: n They are adequate to know the causes of an outcome. n To know the natural history of disease. n They adequate when the exposure is rare. n They are useful when we study two or more outcome at the same time. n Disadvantages: n They take a long time. n They are expensive. n Subjects can be lost in the follow up. n They are not adequate for study rare outcomes.

Cross sectional studies Exposed with outcome Subjects selected to study Exposed without outcome Non-exposed without outcome Beginning of study

Cross sectional studies n Analyze data of a subjects group in a point of time. n Describe a disease and its importance for the population. n Define the needed on health. n They can be classified in: Descriptive n Analytic n

Cross-sectional studies n Advantages: n They are useful to know the burden of a disease in a group. n Useful to evaluate diagnostic procedures. n To study common risk factors. n To study common outcomes. n Disadvantages: n Populations little willing to collaborate. n The sample can not be representative from the population. n It is not useful to search causes of the outcome.

Experimental studies n Classification n Randomized clinical trials. n Quasi experimental. n With historic controls.

Experimental studies Outcome Exposed Without outcome Subjects that participate Outcome Without outcome Controls Beginning of study Intervention Time

Experimental studies n They are called clinical trials. n It is administrated an intervention to a group, randomize selected and we do not know what is receiving (blind). The group that does not receive the intervention, it is a control group. n The allocation of subjects in experimental or control group is given by chance. n By ethics reasons, only it is permitted beneficial interventions.

Experimental studies n Blind single is when the subjects do not know what intervention are receiving. n Double blind is when neither subjects nor researcher know what intervention are receiving each subject.

Experimental studies n Cross-design n There are clinical trials with auto controls. n The same group work as control group.

Experimental studies n There are cross design where it is administrated an intervention (1) to experimental group and another (2) in a control group. n After, interventions are suspended, and left a space (wash out period) without it, then the intervention 1 is administrated to control group and intervention 2 is administrated to experimental group.

Experimental studies Outcome Controls Experiment al group Subjects that participate Without outcome Outcome Controls Without outcome Outcome Experiment al group Without outcome Beginning of study Intervention Time

Experimental studies n There are clinical trials with external controls. n We compare the results with the results of another researcher or with the results of a previous study. n Also, they are called historic controls.

Experimental studies With outcome Subjects Without outcome With outcome Results of a previous study Without outcome Beginning of study Intervention only in subjects Time

Experimental studies n Advantages: n Give strong evidence of causality. n There are less bias. n Historic controls are used in preliminary studies. n Disadvantages: n Inappropriate use of historic controls lead a severe mistakes. n Expensive. n They need time.

Ecologic studies n Compare exposure and the outcome between groups. n Measure the exposure and outcome, in the group as all. n They are only studies that offer to study differences between groups.

Ecologic studies n Advantages: n Fast n Cheap n Use routinely data n Disadvantages: n They did not take into account to the individual. n They depend on the quality of routinely data n They are difficult to interpret.

Bibliography n 1. - Gordis L. Epidemiology. Phialdelphia, W. B. Saunders Company, 1996. n 2. - Songer T. Study designs in epidemiologic research. Supercourse, 2005 (http: //www. pitt. edu/~super 1/lecture/lec 19101/ index. htm) (Accesed October 2008). n 3. - Hennekens CH, Buring J, Mayrent SL. Epidemiology in Medicine. Boston, Little Brown and Company, 1987.