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Subgroup analysis on a factor with levels identical to feature levels produces wrong estimates #22

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leeper opened this Issue Mar 15, 2019 · 1 comment

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leeper commented Mar 15, 2019 •
edited

Moved from @m-jankowski at #13:

This is also a problem when using mm_diffs().

In my case, I wanted to conduct a subgroup analysis conditional on the gender of the respondents (labeled as "Male" or "Female"). The conjoint experiment, however, also contained levels with these labels ("Male" and "Female"). Particularly problematic is that mm_diffs() did not throw an error message, but returned wrong estimates without any warnings.

Here is an artificial example using the immigration data:

# Data
data("immigration")

# Create subgroups
immigration$ethnosplit <- cut(immigration$ethnocentrism, 2)

# Rename subgroup levels
immigration$subgroup <- as.factor(ifelse(as.numeric(immigration$ethnosplit) == 1, 
                                          "Female", 
                                          "Male"))

# Estimate correct MMs by subgroup
mm_correct <- cj(na.omit(immigration),
                 ChosenImmigrant ~ Gender + Education + LanguageSkills,
                 estimate = "mm",
                 id = ~ CaseID, 
                 by = ~ ethnosplit)

plot(mm_correct,
     group = "ethnosplit",
     vline = 0.5)

image

# Differences between subgroups

mmdiff_correct <- mm_diffs(na.omit(immigration), 
                   ChosenImmigrant ~ Gender + Education + LanguageSkills,
                   id = ~ CaseID, 
                   by = ~ ethnosplit)

plot(mmdiff_correct)

image

# Using subgroups with identical level names returns wrong estimates

mmdiff_problem <- mm_diffs(na.omit(immigration),
                   ChosenImmigrant ~ Gender + Education + LanguageSkills,
                   id = ~ CaseID, 
                   by = ~ subgroup)

plot(mmdiff_problem)

image

@leeper leeper added bug help wanted labels Mar 15, 2019

@leeper leeper referenced this issue Mar 15, 2019

Open

Same factor levels in different attributes #13

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leeper commented Mar 15, 2019

This can probably be solved by specifying left-hand-side assignments that use the feature name and the level name rather than just the level name (which have been incorrectly assumed to be unique): https://github.com/leeper/cregg/blob/master/R/mm_diffs.R#L51-L90

@leeper leeper closed this in e79b0aa Apr 7, 2019

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