1# chichi_shu *That makes variable respond binary, i.e., either 1 when (old) respond =1 or 0 otherwise.Considering you use a WEIGHT statement of 'smp_wgt', PROC FREQ assumes that an observation represents smp_wgt observations , where smp_wgt is a number of either 1 or 10 here.  
If you do not specify a WEIGHT statement, each observation has a default weight of 1. The sum of the WEIGHT variable values represents the total number of observations.
For further illustrating this question, an example was following by:

obs reponse smp_wgt
1    1             10
2    0              1

in this case,
if specifying weight of smp_wgt, then total # of observations =1*10 +1*1 =11, % of (respond =1) =10/11;
if not specifying weight, then total # of observations =1*1 +1*1 =2, % of (respond =1) =1/2

楼上老大太nice了！
谢谢！