この節の作者: Rebecca Vederhus, Sebastian Jentschke
From SPSS to jamovi: Non-parametric analyses¶
This comparison shows how a Wilcoxon signed-rank test is conducted in SPSS and jamovi. The SPSS test follows the description in chapter 7.5.2 in Field (2017), especially figure 7.9 and output 7.3 - 7.4. It uses the data set Drug.sav which can be downloaded from the web page accompanying the book.
SPSS | jamovi |
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In SPSS, first split the file using Data → Split File . |
In jamovi, the file can be split using: Variables → Filters . In the
window that appears, write = Drug == "Ecstasy" and then save the output.
Open the original file again and repeat these steps but write the following
command instead: = Drug == "Alcohol" . Now you will have two separate
files, one for each drug. |
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In the Split File window, click Organize output by groups . Then, move
the Drug variable to the box called Groups Based on . Lastly, click
Sort the file by grouping variables . |
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Then, create a Mann-Whitney test using: Analyze → Nonparametric Tests
→ Related Samples . |
Within each file, use the following steps to create a Wilcoxon signed-rank
test: Analyses → T-tests → Paired Samples T-Test . |
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In the Nonparametric Tests window, open Fields and click Use custom
field assignments . Move the Sunday and Wednesday variables to the
Test Fields box. |
In jamovi, mark Sunday_BDI and Wednesday_BDI and move them to the
Paired Variables box. Then, tick the box for Wilcoxon rank . Repeat
this procedure for both output files. |
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Lastly, open Settings and click Customize tests . Tick the box for
Wilcoxon matched-pair signed-rank as shown in the picture below. |
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Comparisons of the output show that the results in SPSS and jamovi are slightly different. | |
In SPSS, the first output table is the model summary, which only shows the
p-value for the test. If you double-click this table, you get the details
of the analysis. There are two model summaries, on for each drug condition.
The Wilcoxon Signed Rank test show the following values: Total N , Test
Statistic , Standard Error , Standardized Test Statistic and
Asymptotic Sig. (2-sided test) . |
In jamovi, there are two output files, with a table each. In contrast to
SPSS, the Paired Samples T-Test table only displays the test statistic
and its significance value. |
When comparing the output, none of the numerical values are the same. The reason for the difference in p-values is that jamovi applies continuity correction (where a discrete distribution – ranks – is approximated via a continuous one – the standard normal distribution) whereas SPSS doesn't. | |
If you wish to replicate those analyses using syntax, you can use the commands below (in jamovi, just copy to code below to Rj). Alternatively, you can download the SPSS output files and the jamovi files with the analyses from below the syntax. | |
NPTESTS
/RELATED TEST(Sunday_BDI Wednesday_BDI) WILCOXON
/MISSING SCOPE=ANALYSIS USERMISSING=EXCLUDE
/CRITERIA ALPHA=0.05 CILEVEL=95.
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jmv::ttestPS(
data = data,
pairs = list(
list(i1 = "Sunday_BDI", i2 = "Wednesday_BDI")),
students = FALSE,
wilcoxon = TRUE)
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SPSS output file containing the analyses | jamovi file with the analyses for Alcohol jamovi file with the analyses for Ecstasy |
References
Field, A. (2017). Discovering statistics using IBM SPSS statistics (5th ed.). SAGE Publications. https://edge.sagepub.com/field5e