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Chapter 3 Description of qualitative variable
Quantitativevariable
Qualitativevariable
Multiple categoricalvariable
Ordinal variable
variable
Binaryvariable
review
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
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
categoriesYour opinion on something:
unsatisfactory, normal, very satisfactory
review
To keep things simple, we begin with table 1 that shows
the relative numbers of a kind of infection disease in a
city.
Table 1 The relative numbers of a kind of infection disease in a city
District
（1）
Population
（2）
Number of
the patient
（3）
Ratios
（4）
Proportions
（%）
（5）
Rates
（1/100
thousand）
（6）
1 636723 2433 — 18.9 382
2 389540 3033 1.25 23.5 779
3 699712 1650 0.68 12.8 236
4 328363 1503 0.62 11.6 458
5 286967 1282 0.53 10.0 447
6 317504 1853 0.76 14.4 584
7 153838 1130 0.76 8.8 735
total 2812647 12884 — 100.0 458
1. Count - The number of individuals with the outcome of interest
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)
Table 1 The relative numbers of a kind of infection disease in a city District
（1）
Population
（2）
Number of the patient
（3）
Ratios
（4）
Proportions （%） （5）
Rates （1/100
thousand） （6）
1 636723 2433 — 18.9 382 2 389540 3033 1.25 23.5 779 3 699712 1650 0.68 12.8 236 4 328363 1503 0.62 11.6 458 5 286967 1282 0.53 10.0 447 6 317504 1853 0.76 14.4 584 7 153838 1130 0.76 8.8 735
total 2812647 12884 — 100.0 458
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
9.1812884
2433
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.
Tabl e 1 The rel ati ve numbers of one ki nd i nfecti on di sease i n a ci ty
Di stri ct
（1）
Popul ati on
（2）
Number of
The pati ent
（3）
Rati os
（4）
Proporti ons
（%）
（5）
Rates
（1/ 10万）
（6）
1 636723 2433 — 18. 9 382
2 389540 3033 1. 25 23. 5 779
3 699712 1650 0. 68 12. 8 236
4 328363 1503 0. 62 11. 6 458
5 286967 1282 0. 53 10. 0 447
6 317504 1853 0. 76 14. 4 584
7 153838 1130 0. 76 8. 8 735
total 2812647 12884 — 100. 0 458
thousand-100/382100000636723
2433
4. Ratio - One number divided by another number
Tabl e 1 The rel ati ve numbers of one ki nd i nfecti on di sease i n a ci ty
Di stri ct
（1）
Popul ati on
（2）
Number of
The pati ent
（3）
Rati os
（4）
Proporti ons
（%）
（5）
Rates
（1/ 10万）
（6）
1 636723 2433 — 18. 9 382
2 389540 3033 1. 25 23. 5 779
3 699712 1650 0. 68 12. 8 236
4 328363 1503 0. 62 11. 6 458
5 286967 1282 0. 53 10. 0 447
6 317504 1853 0. 76 14. 4 584
7 153838 1130 0. 76 8. 8 735
total 2812647 12884 — 100. 0 458
68.02433
1650;25.1
2433
3033
Exercise
Year Num of ill Num of death Mortality rate
(%)
Proportion of
death (%)
1993 584 8
1994 571 10
1995 714 12
1996 748 16
1997 942 21
1998 1095 24
Total 4654 91
Exercise （ answer)
Year Num of ill Num of death Mortality rate
(%)
Proportion of
death (%)
1993 584 8 1.37 8.8
1994 571 10 1.75 11.0
1995 714 12 1.68 13.2
1996 748 16 2.14 17.6
1997 942 21 2.23 23.0
1998 1095 24 2.19 26.4
Total 4654 91 1.96 100.0
