Title

rspeedindex -- Computation of a response speed index and outlier identification

Syntax

rspeedindex varlist [if exp] [in range]
[, options]

where varlist is a list of numeric response time
variables.

Required
indexname(newvar) generates a variable for the response speed index

flagname(newvar) generates a flag variable for response speed outliers

cutoffmethod(string) defines the method for the identification of response
speed outliers. It can either be percent, mean, or absolute.

Optional
lowercutoff(numlist) defines a lower cutoff for the identification of response
speed outliers (i.e., fast respondents).
If cutoffmethod is percent, cutoff values are percentiles. Valid values are 1, 5, 10, or 25.
If it is mean, cutoff values are standard deviations from the mean of the distribution
and have to be in the range of 0 >= x <= 5.
If it is absolute, cutoff values are absolute index values and have to be in the range of 0 >= x <= 1.

uppercutoff(numlist) defines an upper cutoff for the identification of response
speed outliers (i.e., slow respondents).
If cutoffmethod is percent, cutoff values are percentiles. Valid values are 75, 90, 95, or 99.
If it is mean, cutoff values are standard deviations from the mean of the distribution
and have to be in the range of 0 >= x <= 5.
If it is absolute, cutoff values are absolute index values and have to be in the range of 1 >= x <= 2.

Optional
missing(numlist) list of missing values in response time variables

quietly suppresses the output of additional descriptives

Description

The rspeedindex command computes a response speed index on the
basis of question block, page or item level response times in survey data.
The index values can be interpreted as a measure of the mean response speed of
survey respondents. An index value of 1 is equivalent to the mean of the
respondents´ mean response speed over the variables in varlist
in the selected sample of respondents. Index values close to 0 indicate a very
fast mean response speed, whereas values close to 2 indicate a very slow mean
response speed.

Furthermore, the rspeedindex command generates a variable to flag
response speed outliers. Thereby, it can be specified whether response speed outliers
in the lower (i.e., fast respondents), the upper (i.e., slow respondents), or both
directions are detected. Three different methods to generate cutoff values for the
identification of response speed outliers are available. These include the use of
percentiles, standard deviations from the mean of the distribution, and absolute
values of the response speed index.

The response times variables specified in varlist are
preferably question block, page or item level measures. Ideally, response times
are measured on the item level, have a high resolution (s or ms), and are
available for every item in the survey.

Examples

Quietly computing the response speed index for all respondents on the basis of
ten response time variables. Respondents in the lower decile of the response speed index
are flagged as response speed outliers.

. rspeedindex rtvar1-rtvar10, index(rspeedindex)
flag(outlier) cut(percent) lo(10) quietly

Quietly computing the response speed index for respondents who completed
the survey on the basis of thirty response time variables. Respondents with index values
that are (more than) two standard deviations below or above the mean are flagged as
response speed outliers.

. rspeedindex rtvar1-rtvar30 if complete==1, index(rspeedindex)
flag(outlier) cut(mean) lo(2) up(2) quietly

Quietly computing the response speed index for all respondents on the basis of
a single response time variable. Respondents with index values lower than .5 are
flagged as response speed outliers.

. rspeedindex rtvar1, index(rspeedindex)
flag(outlier) cut(absolute) lo(.5) quietly

References

Roßmann, J. (2010): Data Quality in Web Surveys of the German
Longitudinal Election Study 2009. Paper presented at the 3rd ECPR Graduate
Conference, Dublin, 30.08.-01.09.2010.

Roßmann, J. (2012): Zeitunterschreiter in Web-Befragungen der GLES:
Messung und Bedeutung für die Identifikation von Satisficern. [Speeding
respondents in web surveys of the GLES: Measurement and implications for
the identification of satisficing respondents.] Unpublished paper.

Author

Joss Roßmann, GESIS - Leibniz Institute for the Social Sciences, joss.rossmann@gesis.org

Recommended citation (APA Style, 6th ed.):

Roßmann, J. (2015): RSPEEDINDEX: Computation of a response speed index and
outlier identification (Version: 0.4) [Computer Software].
Chestnut Hill, MA: Boston College.

Acknowledgments

The author would like to acknowledge the support of GESIS - Leibniz
Institute for the Social Sciences for the support in the creation of this
Stata module.