Sunday, October 3, 2010

What's a PPT? Part 2

Continued - and again, not an easy read - but a funny guy!  BLUF: skip the fiber, unless you just like to be flatulent.

"I now want to look at what happened in the intervention arm. We can tease out a sub group, the folks who really complied with the intervention, and compare them with the people in the intervention arm who complied poorly.  That's this subgroup analysis.
"A total of 210 "super compliers" were noted and compared to controls. I can't really tell if the controls were on the SAD or were those less compliant members of the intervention arm, probably the latter. The odds ratio for adenoma recurrence of supercompliance was 0.65 and statistically significant.
"So 210 people out of the 1,905 in the intervention arm benefited. That means that 1,695 people didn't benefit from four years of advice.

----------------------------------------------------------------------------------------------------------------------------"Counter intuitive isn't it? But science does that sometimes. Just look at the money spent on supporting the long dead hypothesis that eating leaves is in some way beneficial for humans. There's a powerful need for self justification of the pig's-ear that PPT turned out to be. Depending on your point of view of course!"
"But hold on a minute. When the initial study compared intervention with non intervention there was no benefit from intervention compared to the SAD. So if 210 people did better than average, then 1,695 people MUST HAVE DONE WORSE than average. That is, they did worse than those on the SAD. You would have expected a 50:50 split, obviously half should do better and half should do worse than average!
EDIT: Of course if they compared 210 super compliers to the 1,695 injured people they possibly got p= 0.05 because these 1,695 did particularly badly. I wonder if p would have been =0.05 if they had compared the 210 to the whole SAD group? Probably not would be my guess. Or they would have done it! Me, cynical? Surely not... END EDIT.  We can summarise: 1,695 people were injured by being in the intervention arm of the PPT. I would also point out that "super compliers" are super compliers. These are the sort of people who meticulously take their placebo tablets in clinical trials and consistently do better than those who are lackadaisical with consuming their placebo tablets. Mike Eades has blogged about it nicely here. So did the 210 super compliers benefit from the diet or were they just the sort of people who comply with authority and automatically do well despite their doctor's best efforts? There was no scope for an adherer effect in the SAD non-intervention arm because they were left alone with no religious group therapy support. Oops, I mean dietary advice... So was everyone injured in the intervention group but a few had their injury offset by the warm glow of study compliance? Don't hold your breath waiting to see THAT get discussed in an NIH funded paper. We're looking to justify the cash spent on a superb study which has made no friends among people with control over the purse strings... Anyhow, back to HCy. We all know from nauseous observational stuff that PPT intervention should have dropped HCy (I've not seen this analysis anywhere yet but I guess it did) but it still didn't drop adenoma recurrence and it probably worsened it in that vast majority of the participants who weren't super compliers. What sort of HCy levels are present in the SAD arm of PPT and how do they stratify against adenoma recurrence risk? This is from the sub analysis of the control arm I wrote about earlier: To summarise the right hand column, folks with no relapse had median HCy around 12.5micromol/l. Those groups with the worst recurrences generally had median HCy over 14micromol/l. Low HCy is "associated", observationally, with lower adenoma relapses. Of course those who ate the most plants, fibre and general pre-poop had the lowest HCy... Really begs why the trial totally flopped. Something to do with the difference between observational studies and intervention studies I think! There may be no funding for basic science (ask my wife!) but there seems to be plenty for this sort of dogma support BS! However, within the dogma that HCy is controlled by eating leaves, how bad must it get if you eat almost no plants, with the emphasis on peeled potatoes when you do indulge in vegi-cide, as little fibre as possible and as much animal fat as practical, say 70% of calories?
Well the HCy comes out, when eating to the Optimal Diet, with a median of about 10.7micromol/l. And relatively few plants were murdered (blame Elizabeth) in the process.
No leaves, no fibre, lots of saturated fat. The occasional spud. Please remember that the data from the OD is observational in nature too. You have to guess what the HCy level was pre OD.

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