SPSS and SAS macro for computing Krippendorff’s alpha
Written by Andrew F. Hayes
The
For a copy of the paper that introduces this macro, click here.
Here is an SPSS version of the data in Table 1 from the Communication Methods and Measures paper (Hayes & Krippendorff, 2007).
Can’t get the macro to work? Click here.
To cite this paper and/or macro in APA Format: Hayes, A. F., & Krippendorff, K. (2007).
Answering the call for a standard reliability measure for coding data. Communication
Methods and Measures, 1, 77-89.
For details on the bootstrapping algorithm used in this macro, click here.
Can’t get the macro to work? Check here.
This page describes version 2.1
of the macro, uploaded on
This macro computes Krippendorff's alpha reliability estimate for judgments made at any level of measurement, any number of observers, with or without missing data. The macro assumes the data file is set up in an SPSS data file with judges as the variables and the units being judged in the rows. The image below represents how the data in Krippendorff (2004), section 11.3.3 (page 230), would look as an SPSS data file. As can be seen, the entries in the data matrix should be the coding (quantified or numerically coded for nominal judgments) given to the unit in that row by the judge in that column.
Once the macro command set is executed exactly as downloaded (click here to download the SPSS version), the syntax for the macro is
KALPHA judges = judgelist/level = lev/detail = det/boot = z.
where judgelist is a list of variable names holding the names of the judges, lev is the level of measurement (1 = nominal, 2 = ordinal, 3 = interval, 4 = ratio), det is set to 1 if you desire SPSS to print the coincidence and delta matrices (as defined by Krippendorf, 2004), and z is the number of bootstrap samples desired for inference. The '/level', '/detail’ and '/boot' boot subcommands are optional and default to 1,0, and 0, respectively, if omitted. The number of bootstrap samples, if requested, must be at least 1000 and should be a multiple of 1000.
Missing data can be represented as a period (‘.’). Units that are not coded by at least two judges are excluded from the analysis.
Here is example output applied to the data file above, requesting an estimate for nominal data, detailed output:
kalpha judges = obsa obsb obsc obsd/level = 1/detail = 1/boot = 5000.
Run MATRIX procedure:
Krippendorff's
Alpha Reliability Estimate
Alpha LL95%CI
UL95%CI Units Observrs
Pairs
Nominal .7434
.6035 .8600 11.0000
4.0000 55.0000
Probability (q)
of failure to achieve an alpha of at least alphamin:
alphamin q
.9000
.9932
.8000
.7936
.7000
.2940
.6700
.1176
.6000
.0154
.5000
.0000
Number of
bootstrap samples:
5000
Judges used in
these computations:
obsa obsb
obsc obsd
====================================================
Observed
Coincidence Matrix
7.00
1.33 .33 .33
.00
1.33
10.00 1.33 .33
.00
.33
1.33 8.00 .33
.00
.33
.33 .33 4.00
.00
.00
.00 .00 .00
3.00
Expected
Coincidence Matrix
1.85
3.00 2.31 1.15
.69
3.00
4.00 3.33 1.67
1.00
2.31
3.33 2.31 1.28
.77
1.15
1.67 1.28 .51
.38
.69
1.00 .77 .38
.15
Delta Matrix
.00
1.00 1.00 1.00
1.00
1.00
.00 1.00 1.00
1.00
1.00
1.00 .00 1.00
1.00
1.00
1.00 1.00 .00
1.00
1.00
1.00 1.00 1.00
.00
Rows and columns
correspond to following unit values
1.00
2.00 3.00 4.00
5.00
------ END
MATRIX -----
(Note:
Krippendorff reports on page 232 of his book that alpha = 0.734. This is a typographical error in the book, as
the macro is computing alpha correctly.
On a document on his web page, Krippendorff uses the same data and correctly
reports alpha as 0.743. The macro has
been checked numerous times using many different data files in Krippendorff and
Neuendorf (2002) and different levels of measurement, and it has always worked
and computed alpha correctly.
Nevertheless, if you find an error in the computations produced by the
macro using your own data, let me know).
In order to be included in the computations, at least two observers must code the unit. In the example above, “units” is 11 because unit 12 is excluded (because only a single observer coded that unit). The number of pairs is equal to the number of pairs of judgments that contribute to the computation of alpha.
Problems can occur during bootstrapping that will invalidate the confidence intervals that are produced. When problems are detected during bootstrapping, the macro will let you know and then not produce any output that is based on bootstrap results. You should always check the output file (or, in SAS, the log file) for evidence of errors, and don’t interpret the output if any errors are found, as the macro may still produce output when errors occur.
Download the SPSS version of the macro by clicking here.
Download a SAS version of the macro by clicking here. For the format of the macro command syntax in SAS, see the comments in the code.
References
Hayes, A. F., & Krippendorff, K. (2007). Answering the call for a standard reliability measure for coding data. Communication Methods and Measures, 1, 77-89.
Krippendorff, K. (2004). Content analysis: An introduction to its methodology. Thousand Oaks, CA: Sage.
Neuendorf, K. (2002). The content analysis guidebook. Thousand Oaks, CA: Sage.