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There are different methods to check for outliers or low quality data in survey responses. Protobi even has a [QC tool](http://help.protobi.com/99791-new-and-updated-articles/%22qc%22-tool) that helps you flag respondents based on pre-set conditions like straight-lining. However, there are some quality checks that are more complex and are better written out in [data process](/process-data/start-data-process). One example is using standard deviation to check for straight-liners in a battery of responses.

In the example below, **Q13** is a battery of 7-point scale questions. You could use the QC tool to perform the pre-set [straight-line check](http://help.protobi.com/en_US/99791-new-and-updated-articles/%22qc%22-tool#Straightline%20check-5). However you might consider respondents  who gave very similar responses for each question suspicious in addition to true straight-liners.

In project [Pre-calculate](/process-data/start-data-process) you can define function that calculates the standard deviation between the children of a group.

## Code

//Function used to calculate standard deviation

function std(row, kidKeys) {

var vals = kidKeys.map(function(kidKey) { return row\[kidKey\] });

if (vals\[0\]) var res = d3.deviation(vals)

return res;

}

//Groups/children for which you want to calculate std

var checks = {

"Q13": \["Q13\_1", "Q13\_2", "Q13\_3", "Q13\_4", "Q13\_5"\]

}

//Create new "std\_" variable standard deviation calculation

rows.forEach(function(row) {

for (var key in checks) {

row\["std\_"+key\] = std(row, checks\[key\])

}

});

return rows;

The code above create a new element with **std\_** appended as a pre-fix.  For the distribution below the [round by](http://help.protobi.com/editaccess/bin-numeric-values#%22Round%20by...%22%20dialogue-0) is \[0,0.5,1,3\].

If you click into the zero values in the standard deviation element, you should see that all those respondents were flagged in the straight-line check from the QC tool.

If you click to drill in on respondents with a low standard deviation (e.g. 0.1 - 0.5), you can choose individual **respids** to check. This respondent did not straight-line, but they use the same rating for all but one of the questions in the battery.

## Advanced support

There are complex cases where you might want to flag respondents, not limited to the example in this tutorial. Contact us at support@protobi.com to discuss your specific needs.

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