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# st: mysterious inaccuracy when adding big numbers

 From Trang Nguyen To statalist@hsphsun2.harvard.edu Subject st: mysterious inaccuracy when adding big numbers Date Fri, 8 Apr 2011 10:49:34 -0400

```Hi.

I am working on a dataset with households as observations that are
nested in communes, districts and provinces. I have variables
- province: province number (3 digits)
- district: district number within each province (max 2 digits)
- commune: commune number within each district (max 2 digits)
- household: household number within each commune (max 2 digits)

I wanted to make a unique ID for each household that doesn't repeat
across communes, districts and provinces, that also shows me all the
province/district/commune information. So I did this:
gen ID = province*1000000 + district*10000 + commune*100 + household

I got a variable ID that is correct for the province, district and
commune components, but the last two digits do not match the value of
the household variable. Instead they are 04 or 12 or 20.

below. Thanks much!

. gen ID = province*1000000 + district*10000 + commune*100 + household

. count if ID != province*1000000 + district*10000 + commune*100 + household
7932

. format ID %15.0g

. list province district commune household ID in 1/20

+------------------------------------------------------+
| province   district   commune   househ~d          ID |
|------------------------------------------------------|
1. |      101          1         3          1   101010304 |
2. |      101          1         3          2   101010304 |
3. |      101          1         3          4   101010304 |
4. |      101          1         3          5   101010304 |
5. |      101          1        17          4   101011704 |
|------------------------------------------------------|
6. |      101          1        17          5   101011704 |
7. |      101          1        17          6   101011704 |
8. |      101          1        17          8   101011712 |
9. |      101          1        17          9   101011712 |
10. |      101          1        17         10   101011712 |
|------------------------------------------------------|
11. |      101          1        17         11   101011712 |
12. |      101          3         3          3   101030304 |
13. |      101          3         3          4   101030304 |
14. |      101          3         3          5   101030304 |
15. |      101          3         3          6   101030304 |
|------------------------------------------------------|
16. |      101          3         3          7   101030304 |
17. |      101          5        11          3   101051104 |
18. |      101          5        11          6   101051104 |
19. |      101          5        11          9   101051112 |
20. |      101          5        11         10   101051112 |
+------------------------------------------------------+

. codebook ID

-----------------------------------------------------------------------------------
ID                                                             (unlabeled)
-----------------------------------------------------------------------------------

type:  numeric (float)

range:  [1.010e+08,8.231e+08]        units:  1
unique values:  1308                     missing .:  0/8341

mean:   4.6e+08
std. dev:   2.6e+08

percentiles:        10%       25%       50%       75%       90%
1.1e+08   2.1e+08   4.1e+08   7.1e+08   8.1e+08

Thanks much!

Trang

------------------------
Trang Nguyen
Doctoral student
Johns Hopkins School of Public Health

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```