# Need help with negative proportions in experiment

Hello! I got referred to here by someone from the econometrics subreddit.

I ran an experiment with a treatment and a control group. Treatment group voted under an electoral rule, where voters could cast a negative vote (with a score of -1) and a positive vote (+1). Control group used the standard First-Past-The-Post rule.

I want to compare the results of extreme parties (I know which those are) and see if the difference is significant. However, these extreme parties obtained a negative result, so a normal test of proportion doesn't work. What do I do?

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Kav10
1.9K
• Hey Kav10, Thank you very much for your answer. I will look into the first option, but in the meantime, please clarify something for your second suggestion. If I add a constant to the negative votes, should I not add the same constant to all parties? And once I do, what kind of statistical test should I use to determine whether the difference is significantly different from zero?

• Yes, you should apply the same constant to all parties consistently. This ensures that you're comparing the parties' performance on a common scale. Since you're interested in comparing the differences between two groups (treatment and control), you can use a t-test for paired samples.

• I thought t-tests were only used to compare means. However, I want to compare sums here, not means.

• That’s right. For comparing sums, you can use the Wilcoxon test I explained above.

• My apologies, but then I don’t understand. So how do I use the t-test after adding a constant?

• Not the t-test. The Wilcoxon Test.

• Farmin
-1

In that case, what is the difference between the two approaches you suggested? I’ll have to use a non-parametric test on both occasions.