Problem with rank sum test

[Strekozova Sofia]

Hello, I'm a new user of Stata. In my dataset variable compl_number in each row is the number of all complaints categorised by byte variables IDS, field and so on. When I use ranksum, I get the number of observations of byte variable, but not of variable compl_number. I guess the problem is in the dataset itself because the whole number of complaints is located in one cell in each row and Stata doesn't count it. What can I do in this situation?

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(IDS hosp field financ) int compl_number
1 2 5 1  65
1 1 0 1 320
1 2 1 1  82
1 2 1 2   9
1 2 1 1   2
1 2 3 1   0
1 1 1 1 160
1 1 5 1  87
1 2 1 2  27
1 2 2 1 100
1 2 0 2  15
1 1 1 1   0
1 1 2 1  80
1 1 0 2  30
1 1 3 1 300
1 1 1 2  50
1 2 4 1   0
1 1 5 2  26
1 1 4 1   3
1 1 1 2  10
1 2 0 1  95
1 2 5 2   6
2 1 0 1 542
2 2 5 1 312
2 2 1 1  63
2 1 3 1 600
2 2 2 1 280
2 1 2 2  20
2 2 3 1   2
2 2 3 2   3
2 2 0 1 280
2 1 1 1 452
2 1 3 2 120
2 1 5 1 273
2 2 1 1 248
2 1 2 1 200
end
label values IDS IDS
label def IDS 1 "риск прописан", modify
label def IDS 2 "не прописан", modify
label values hosp hosp
label def hosp 1 "adult", modify
label def hosp 2 "child", modify
label values field field
label def field 0 "не_хир", modify
label def field 1 "лор_стомат", modify
label def field 2 "травма", modify
label def field 3 "акуш", modify
label def field 4 "универ", modify
label def field 5 "хирургия", modify
label values financ financ
label def financ 1 "госуд", modify
label def financ 2 "част", modify

. by hosp, sort : ranksum compl_number, by(IDS)

--------------------------------------------------------------------------------------------------
-> hosp = adult

Two-sample Wilcoxon rank-sum (Mann-Whitney) test

         IDS |      obs    rank sum    expected
-------------+---------------------------------
     риск п� |       11          81       104.5
     не про� |        7          90        66.5
-------------+---------------------------------
    combined |       18         171         171

--------------------------------------------------------------------------------------------------
-> hosp = child

Two-sample Wilcoxon rank-sum (Mann-Whitney) test

         IDS |      obs    rank sum    expected
-------------+---------------------------------
     риск п� |       11        86.5       104.5
     не про� |        7        84.5        66.5
-------------+---------------------------------
    combined |       18         171         171

[Clyde Schechter]

Nothing is wrong with your dataset. And you are using -ranksum- correctly. You are just expecting it to output something that it isn't designed to output. It is not designed to output the total number of complaints. And I don't think anybody writing a program for the rank sum test would include that feature. That's because in general the variable being analyzed in the rank sum test is not a quantitative variable where it makes any sense to add up the totals. The typical application of rank sum is to an ordinal variable, where we can order the responses, but there is no meaningful magnitude associated with them.

So to also output the total number of complaints in each group, you need to modify your code with some additional commands:

levelsof hosp, local(hospitals)
foreach h of local hospitals {
    display _newline(2) `"-> hosp = `:label (hosp) `h''"'
    tabstat compl_number if hosp == `h', by(IDS) statistic(sum)
    ranksum compl_number if hosp == `h', by(IDS)
}

[Strekozova Sofia]

Thank you for explanation, Clyde!