Observational study designs

Case report

detailed description of the signs, symptoms, diagnosis, and treatment of an individual patient

Case series

describes a number of patients with a given disease, greater with 1 person

this group of people have common features such as the characteristics of affected patients

Case report

detailed description of the signs, symptoms, diagnosis, and treatment of an individual patient

Case series

describes a number of patients with a given disease, greater with 1 person

this group of people have common features such as the characteristics of affected patients

case series are oftenly used suggest

emergence of new diseases/ epidemics

previously unknown associations between exposures and outcomes

Pneumocytosis pneumonia

5 young, active, homosexual men were treated for biopsy confirmed pneumocytosis at 3 different hospitals in california. Association suggested bc all patients were homosexuals, must’ve been acquired through sexual contact

limitations of case reports/ case series

impossible to gain strong evidence for causes

• no comparison group for who were not exposed

• esp if assumed cause is common, occurrence of the outcome in people with the exposure may be due to chance

ecological studies

a study in which the units of analysis are populations or groups of people rather than individuals

aggregrate level \

instead of asking each 1st year student we obtain aggregrate data from 20 universities and colleges

an ecologic comparison group

an assessment of the association b/w exposure rates and disease rates during the same time period

why do an ecologic study

individual level data isnt available

often group-level data has already been collected and stored in data archives

If interested in the context of health-how different demographic variables and social environment contribute to mortality or morbidity- ecologic study is a good starting point

Strengths of ecological studies

• Exposuress may truly be population-level 

• Can be easy and inexpensive

  • Often rely on pre-existing data 

• Analysis and presentation are generally simple to understand 

• Can generate new hypotheses for further research

limitations of ecological studies

when a relationship observed at a population level is assumed to occur among individuals 

Potential and alternative explanations cannot be accounted for or tested 

Cross-sectional studies

• Both the exposure and the outcome are determined simultaneously- a snapshot of the study population 

  • Study groups can be based on exposure and the prevalence of outcomes in those exposed and unexposed are compared 

  • Study groups can be based on outcome and the prevalence of the exposure among those with and without the outcome are compared 

• Generally data are collected at an individual level 

Limitations of cross-sectional studies

They yield quantitative estimates of the magnitude of a problem

Don’t measure the temporal ordering of exposure and disease 

Unit of analysis is the person, not a group

strength of cross- sectional studies

helpful in identifying resource needs for health interventions