STATA SUMMATION CODE
STATA SUMMATION FREE

x1) is completely missing for all cases of a particular value of id, then the mean value (e.g. mnx1) that contains the average of the values in x1, within each value of id. bysort id: egen mn`v' = mean(`v') : this line creates a variable (e.g.These variables will end up being substituted for the original data in the -collapse- command (see the -rename- command below). For cases with id = 4, the value of sumx1 is 3. For example, the value of sumx1 is 0 for cases with id = 1 since the missing value in the second case is treated as missing. sumx1) that contains the standard -egen sum()- of the original variable. bysort id: egen sum`v' = sum(`v'): Here, we simply create a variable (e.g.This variable will ultimately help us determine which cases should be given missing data values for the final -collapse- function. So, c2x1 is a 1 for both cases with id = 1 since only one of these cases is a missing value. c2x1), which is the sum of the values we created in the previous two steps, within each level of id. bysort id: egen c2`v' = count(c`v'): Now we create another new variable (e.g.replace c`v' = 1 if(c`v'=0): replace the zeros in our new variable (i.e.

STATA SUMMATION CODE

Stata will code these values as zeros because itвЂ™s default behavior is to evaluate the sum of missing values as 0. cx1) that marks the cases with missing values in the original variable (e.g.

bysort id: egen c`v' = count(`v') if(`v'=.) : Create a variable (e.g.

For each variable x1, x2, and x3, Stata will execute the next set of codes.

foreach v in x1 x2 x3 : This command encompasses the majority of the code block.

bysort id: egen seq = seq() : This line creates a variable ( seq) that counts cases within each value of the id variable.

The code above performs 12 functions in sequence for each variable that we need aggregated (in this case x1, x2,and x3). The critical code is written in the following code block:Д«ysort id: egen c`v' = count(`v') if(`v'=.) To start, weвЂ™ll use the same input data set we used above (all code down to the -end- command). All you need is a little programming skill. It is entirely possible to get around StataвЂ™s natural treatment of missing values in the -collapse sum()- function. Evaluating Collapse Sums with Any Missing Values as Missing So how can you avoid this behavior? The next two sections will cover two additional scenarios. The same thing has happened with the missing input value of x3 in the first row: the summed value is 2, reflecting only the value in the second row of input data. The results show that for id, the missing value (.) for x1 in the second row of input data has been treated as a zero, producing a summed value of zero. The results from your -list- command should look like the figure below. If you are willing to treat missing values as zeros, then using the standard -collapse- command and sum() function is fine.Д®ntering the following syntax in Stata demonstrates this.

Hybrid approach: differentiate between missing and other values, such as zeros.

Evaluate collapse sums with any missing values as missing.

Treat the missings as zeros: what the standard collapse command does.

Most of us will run into this kind of scenario eventually.ДЇortunately, there are a finite number of ways to deal with the problem: If youвЂ™ve never encountered this quandary before, then count yourself lucky. But, this does not always mean it is acceptable to treat the missing data as a zero. For example, a missing value might occur due to survey nonresponse by a respondent. This can be a serious problem if zeros and missing values are substantively different in your data. The basic issue is in the way sum() treats missing data namely, the missing values evaluate to zero.

One of those quirks shows up when using the -collapse- command and the sum() function. Like any program, Stata certainly has its quirks. How Do I Get Stata to Treat Missing Values The Way I Want? In this article, I show three ways Stata can treat missing values when using the -collapse- command and the sum() function. Even the most seasoned Stata users get bit by this quirk every once in a while. It replaced all of the missing values in your data set with zeros!Д«ut thatвЂ™s not at all what you wanted! You wanted those to be missing values, not zeros. That -collapse- command you issued a while back did something rather odd. Your finely-tuned debugging skills kick in, and you track down the problem. The data begin looking like something from one of Lord VoldemortвЂ™s nightmares. That 3-day project you started this morning might actually be completed by the end of the day.ДЄs your fingers fly across the keyboard, you think you can hear Stata singing your praise softly in the background.

STATA SUMMATION CODE

STATA SUMMATION FREE

Stata summation