mcaceresb / stata-pretrends

Power calculations and visualization of pre-trends tests following Roth (2022). (Stata version of the R package of the same name.)
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Negative linear pretrend #3

Closed Alalalalaki closed 9 months ago

Alalalalaki commented 9 months ago

Thank you very much for creating package.

My question is that in my practice, it seems that the generated linear pretrends at 50% or 80% are always upward-slopping curves. For those cases where the treatment effect is negative, shouldn't it be more reasonable to test a downward-slopping pretrend? Please correct me if I am wrong. Thanks!

jonathandroth commented 9 months ago

pretrends power reports the magnitude of the slope of a linear trend for which power is 50%, so it is always positive by construction.

When visualizing hypothesized violations of trends, you can change the sign of the slope if that is appropriate in your context.

On Fri, Dec 1, 2023 at 11:59 AM Xuanli Zhu @.***> wrote:

Thank you very much for creating package.

My question is that in my practice, it seems that the generated linear pretrends at 50% or 80% are always upward-slopping curves. For those cases where the treatment effect is negative, shouldn't it be more reasonable to test a downward-slopping pretrend? Please correct me if I am wrong. Thanks!

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Alalalalaki commented 9 months ago

@jonathandroth Thanks for the fast reply! I see, the magnitude makes sense. And yes I can simply change the sign before the plot code.