1. Chapter 3 Description of qualitative variable

2. Quantitative variable Qualitative variable Multiple categorical variable Ordinal variable Binary variable review

3. qualitative variable  also known as categorical or nominal  is one that can not be measured in the usual sense ， only can be categorized  convey information regarding attribute review

4.  Binary variable: gender, live or death, yes or no.  Multiple categorical variable blood types race A, B ， AB, O white, black, yellow, brown  Ordinal variable: there is an order in the categories Your opinion on something: unsatisfactory, normal, very satisfactory review

5. To keep things simple, we begin with table 1 that shows the relative numbers of a kind of infection disease in a city. Relative number rateproportionratio

6. 1. Count - The number of individuals with the outcome of interest

7. 2. Proportion - The number of individuals(patients) within a defined group(district) divided by the number of individuals enumerated in the population(total of the patient)

8. a = number who develop disease within a defined group a+b+c+… = total number who develop disease Proportion = a a + b+c+… 0  Proportion  1

9. 3. Rate - The number of individuals within a defined group who develop disease divided by the number of individuals enumerated in the population at risk.

10. 4. Ratio - One number divided by another number

11. Exercise

12. Exercise （ answer)