Pack-years smoked概念为年包，数值＝吸烟量*吸烟年数；是个连续性变量，但我们处理的时候通常按照分类变量放到SAS中处理．有点实验室常规以30为分界点，即：Group I:<=30Gruop II:<30<=60;Group III:>60;在SPSS中建立Packyears变量，然后用四分位数或者其他分法进行分级分级多少要看你的DATA的fr...
My dad smoked; he didn’t want me to smoke but my friends kept saying I was stupid. They asked when I was going to grow up. So I started when I was sixteen and after a month I couldn’t stop. But two years later I could feel what smoking was doing to me. I couldn’t run ...