Rich Morris
@sometimesdata.bsky.social
Senior research scientist in mental health and wellbeing, looking for an excuse to #rstats
That seems smart
November 28, 2025 at 10:57 PM
That seems smart
That makes more sense than the ANCOVA to me. But my thinking is you want the effect of time because that is the only variable in the implicit DAG which is producing the change.
November 28, 2025 at 5:35 AM
That makes more sense than the ANCOVA to me. But my thinking is you want the effect of time because that is the only variable in the implicit DAG which is producing the change.
Devils advocate if there is no treatment group ANCOVA is the wrong choice. It answers if pre predicts post. You want if measure changes over time. Second model does that.
November 27, 2025 at 9:35 PM
Devils advocate if there is no treatment group ANCOVA is the wrong choice. It answers if pre predicts post. You want if measure changes over time. Second model does that.
That's a tough decision to go through, but getting a PhD can sometimes be an albatross around your neck. It can be hard to know what the good and bad choices are while you are making them - bad luck now can look like a good choice in a few years time and we are all navigating by the rear view mirror
November 27, 2025 at 1:40 AM
That's a tough decision to go through, but getting a PhD can sometimes be an albatross around your neck. It can be hard to know what the good and bad choices are while you are making them - bad luck now can look like a good choice in a few years time and we are all navigating by the rear view mirror
Reposted by Rich Morris
America is great when kids can't play soccer because the secret police may steal their parents
October 12, 2025 at 6:46 PM
America is great when kids can't play soccer because the secret police may steal their parents
That’s what drove me to always declare the method!
October 2, 2025 at 5:56 AM
That’s what drove me to always declare the method!
plot provided by @Chris_said
October 1, 2025 at 9:49 PM
plot provided by @Chris_said
Major depressive episodes among US teenagers peaked in 2021 and have been declining since. More evidence challenging simplistic theories of teen mental health
October 1, 2025 at 9:49 PM
Major depressive episodes among US teenagers peaked in 2021 and have been declining since. More evidence challenging simplistic theories of teen mental health
I did not plan to read all 240 posts on observational evidence today. I did not WANT to read all 240 posts on observational evidence today. What did you do today? Sigh…
September 9, 2025 at 5:32 PM
I did not plan to read all 240 posts on observational evidence today. I did not WANT to read all 240 posts on observational evidence today. What did you do today? Sigh…
that seems like an odd design for an RCT (would it really be an RCT?). Do you have any real world examples in mind or were you just offering a thought experiment to challenge my (our?) assumptions?
September 5, 2025 at 7:25 PM
that seems like an odd design for an RCT (would it really be an RCT?). Do you have any real world examples in mind or were you just offering a thought experiment to challenge my (our?) assumptions?
If we distinguish along those lines, then ANCOVA is always preferred when we have a clear expectation the groups do not differ at baseline (eg RCT). Where I'm unclear is the observational case when groups may differ and we want to decide whether to equate differences with ANCOVA (or matching etc)
September 4, 2025 at 4:49 PM
If we distinguish along those lines, then ANCOVA is always preferred when we have a clear expectation the groups do not differ at baseline (eg RCT). Where I'm unclear is the observational case when groups may differ and we want to decide whether to equate differences with ANCOVA (or matching etc)
this would also help me understand @f2harrell.bsky.social position on this issue better. (Frank have you ever written anything on Lord's paradox I could read somewhere?)
September 4, 2025 at 4:45 PM
this would also help me understand @f2harrell.bsky.social position on this issue better. (Frank have you ever written anything on Lord's paradox I could read somewhere?)
(I actually thought the paper in the op was really helpful but found the more subtle logical inferences too difficult to follow)
September 4, 2025 at 4:41 PM
(I actually thought the paper in the op was really helpful but found the more subtle logical inferences too difficult to follow)
I think someone posted earlier that medicine is concerned with the expected effect of an intervention in the population (so ANCOVA), while education/etc is concerned with compensatory effects among subgroups (so change scores). Would like to hear if that is explained somewhere
September 4, 2025 at 4:41 PM
I think someone posted earlier that medicine is concerned with the expected effect of an intervention in the population (so ANCOVA), while education/etc is concerned with compensatory effects among subgroups (so change scores). Would like to hear if that is explained somewhere
is there an easy distinction between the questions to help understand the differences here?
e.g., Does strength training compensate for differences between men and women? vs does training increase strength in men and women?
e.g., Does strength training compensate for differences between men and women? vs does training increase strength in men and women?
September 4, 2025 at 4:41 PM
is there an easy distinction between the questions to help understand the differences here?
e.g., Does strength training compensate for differences between men and women? vs does training increase strength in men and women?
e.g., Does strength training compensate for differences between men and women? vs does training increase strength in men and women?
I'm trying to understand the wrinkles you mention here. Taking your off-the-cuff eg, using ANCOVA with baseline strength would potentially introduce regression-to-the-mean (RTM) effects right? Because ANCOVA would compare post score strength in weak men to strong women... and so produce a biased ATE
September 3, 2025 at 8:41 PM
I'm trying to understand the wrinkles you mention here. Taking your off-the-cuff eg, using ANCOVA with baseline strength would potentially introduce regression-to-the-mean (RTM) effects right? Because ANCOVA would compare post score strength in weak men to strong women... and so produce a biased ATE
That's a good point. However so far that has been mostly unsuccessful hasn't it? I recall it broke grok and they had roll back the changes...
August 2, 2025 at 1:04 AM
That's a good point. However so far that has been mostly unsuccessful hasn't it? I recall it broke grok and they had roll back the changes...
how on earth does anyone search up for details for useR! ??? Google just returns a list of results about user groups etc...
July 30, 2025 at 3:01 AM
how on earth does anyone search up for details for useR! ??? Google just returns a list of results about user groups etc...
Further evidence of my assertion that most of the useful information on the internet is still text. Just need a browser which presents text
July 11, 2025 at 3:25 PM
Further evidence of my assertion that most of the useful information on the internet is still text. Just need a browser which presents text
