Epidemiology module of practical skills for mbbs student

Measurement - Defining variables

Characteristics of the variables to be used in a study are key in determining what instruments will be used, the size of the population to be studied and how the results will be analyzed.

Specifying the type of variable
The following are outcome variables frequently used in studies of lung health. Please indicate the type of each variable:

Variable	Type
Tuberculosis
FEV1 level
Tuberculin reaction
Pneumonia
Asthma severity
Smear positive TB
Lung cancer
Emphysema
ARI

The following are a number of factors or determinants often studied for their association with lung diseases. Indicate the type of each variable:

Variable	Type
Poverty
Bacterial exposure
Tobacco smoking
Dust exposure
Gender
Age
Ethnic group
Height
Immune competence

Which of the variables listed above could be expressed in different forms (eg. as either categorical or continuous?)

Give an example of a categorical measure of ‘poverty’ and a continuous measure of ‘poverty’.
Definition of variables
Consider the following list of definitions of tuberculosis used in articles published in the International Journal of Tuberculosis and Lung Disease, from the first quarter of 1999

Reported patients with sputum smears positive for acid-fast bacilli in Botswana

A patient with a definitive diagnosis of pulmonary (positive culture and / or clinical and radiological diagnosis) and / or extra-pulmonary tuberculosis (positive culture) in London

3. Tuberculosis diagnosed on the basis of clinical, radiological, or microbiological results in Italy

Tuberculosis confirmed by acid-fast bacilli positivity on smear or culture, and / or granulomatous inflammation with caseous necrosis in the pulmonary biopsy specimen in Turkey

5. Isolates of Mycobacterium tuberculosis in the Netherlands

Every newly-diagnosed tuberculosis patient in New Caledonia confirmed on culture in the Institut Pasteur

7. All patients commencing treatment for tuberculosis in two districts of Uganda

Is it possible to conclude something about “tuberculosis” by simply summarizing the conclusions of all these studies?

Is it the same disease being referred to in each of these studies?

What “elements” are common to each of these definitions?

If you were going to list results or attributes from each of the studies that are comparable across all studies, how would you do it?