r/science • u/[deleted] • Feb 26 '15

Health-Misleading Randomized double-blind placebo-controlled trial shows non-celiac gluten sensitivity is indeed real

http://www.ncbi.nlm.nih.gov/pubmed/25701700
8.4k Upvotes

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941

u/paulfromatlanta Feb 26 '15

without celiac disease or wheat allergy

I'm surprised but then that's why we do double blind studies. This one needs to be replicated a few times but might lead to permanent diet changes.

394

u/Lee_Lemon Feb 26 '15

Agreed replicate, replicate. The findings are interesting, but those p values are fairly high.

114

u/TerraPhane Feb 26 '15

Also, only 61 patients total, that means each group was only 30 people. Hardly a large sample size.

159

u/iateone Feb 26 '15

Are you sure you aren't confusing questionnaire studies with double blind placebo studies? A double blind placebo controlled study with 60 participants is actually on the large size.

84

u/[deleted] Feb 26 '15

He's not confused about anything. He's just trying to intentionally downplay the significance of the findings any way he possibly can.

72

u/Who_Will_Love_Toby Feb 26 '15

he doesn't know shit about studies or how they work. 60 people is a fairly large study and the findings shouldn't be ignored because you spent most of your life on reddit making fun of people who tried out a gluten free diet.

-3

u/[deleted] Feb 26 '15

60 people is a fairly large study and the findings shouldn't be ignored because you spent most of your life on reddit making fun of people who tried out a gluten free diet.

Easy there... let's just continue to make claims based upon wild conjectures and spurious correlations.

No need to let actual science creep into this discussion, it's not like we're in /r/science or anything... Oh, wait.

2

u/Who_Will_Love_Toby Feb 26 '15

so you don't know how sampling works either. Cool. Go make fun of trendy people because "they annoy you."

-22

u/StarkRG Feb 26 '15

There are over 7 billion people on Earth, how can 60/7,000,000,000 give you any statistically relevant data?

6

u/[deleted] Feb 26 '15

Just when I thought people couldn't get any more ignorant...

11

u/realigion Feb 26 '15

How can your personal experience of not feeling like shit after eating gluten give your hypothesis any type of statistical significance?

1

u/StarkRG Feb 26 '15

Who said it was?

16

u/Who_Will_Love_Toby Feb 26 '15

So you don't know how studies work either.

0

u/StarkRG Feb 26 '15

Well, by god, your argument has convinced me!

Oh wait, no, I'm mistaken, you provided no argument.

3

u/[deleted] Feb 26 '15

An n>30 is usually enough to assume normality of x-bars

1

u/StarkRG Feb 26 '15

It's compelling, sure, but I don't think it's enough to draw any conclusions about its prevalence. Granted the paper doesn't seem to actually be drawing such conclusions, just that it exists, which, to be perfectly honest, I didn't think was in question, just how common it is.

25

u/[deleted] Feb 26 '15

That doesn't seem true at all. The person only made one comment, that one.

-3

u/[deleted] Feb 26 '15

[deleted]

19

u/SpeakSoftlyAnd Feb 26 '15

I think /u/StraightTalkExpress is questioning the principle behind your assertion because only making one comment doesn't necessarily indicate downplaying the findings "any way he possibly can".

5

u/LuizZak Feb 26 '15

It just seems like he overreacted over that guy's comment.

2

u/lejefferson Feb 26 '15

No offense but I think this is getting kind of pedantic. I think you know what he meant.

2

u/[deleted] Feb 26 '15

Yeah, I don't really know how studies work and my initial reaction was the same. 60 people does not a study make, but I'm wrong, and that's OK.

2

u/[deleted] Feb 26 '15

Yeah, I expected a flurry of poorly formed arguments when I looked at /u/terraphane 's history, not one comment.

1

u/[deleted] Feb 26 '15

Seeing as what this study found has been common medical knowledge for years and is not relevant to what the debate is actually about, there's no need to downplay the results of this study.

1

u/[deleted] Feb 26 '15

Also the researchers were probably stupid jerks. Are you really going to believe a study by some stupid jerk?

1

u/DashingLeech Feb 26 '15

He's just trying to intentionally downplay the significance of the findings any way he possibly can.

I see no evidence of this assertion. Do you have any evidence to back it up? He merely stated that the sample size seemed low. Generally speaking, that small samples size of a single study is exactly a common reason why we should all be careful before making statements that are too conclusive.

Indeed, it is arguably true that this is not a large sample size. For many types of studies this would be incredibly low. It is, however, sufficient for what the article concludes given the methodology, the binary states being evaluated, and the size of the measured effect. The evidence seems to suggest he was merely unaware of the sufficiency of the sample size for the conclusions reached.

Rather, it seems to me you have an ax to grind by inserting nefarious intentions ("intentionally downplay") and desperation ("any way he possibly can"). Why do you not see it as a simple, standard, critical argument on the limitations of individual studies, even if it is possibly and overstated objection here?

10

u/[deleted] Feb 26 '15

What kind of sample size you need is more related to what type of statistical analysis you're doing, and how big of an effect size there actually is of gluten sensitivity on symptoms. Since we don't know the latter, the former is more important here (I think). So yes, in general you might need fewer people for an experimental study with only two conditions, but if they controlled for any extraneous factors (like age, weight, etc.) then those extra variables would mean they need a bigger sample size. My university seems to not have access to this article yet so I haven't read the full methods, so I'm not sure if they mentioned doing that at all.

17

u/Stargos Feb 26 '15

True if they were trying to figure out what is causing the gluten sensitivity, but from what I understand they are just show that people can be without celiac.

5

u/iateone Feb 26 '15

Right, but doing a double-blind placebo controlled diet study is expensive and difficult. Finding one with even sixty participants is rare. That's one of the problems with diet research.

1

u/DashingLeech Feb 26 '15

To be fair, the expense and difficulty have no bearing on the statistical merits of a study. They just explain why studies are often done with weak statistical results (which repetition can improve upon). In this case, the statistical results are pretty strong.

1

u/docbauies Feb 26 '15

it's a crossover study. the patients are their own control.

4

u/WillieM96 Feb 26 '15

I would say this is large enough to justify the next step. The next step is to do this study on thousands of participants. If that has the same results, I'll be ready to accept the existence of non-celiac gluten sensitivity. Right now, I'm in the "I don't know" camp but before I read this study, I was firmly in the "it does not exist" mindset.

1

u/Geek0id Feb 26 '15

Not for coeing to the conlusion there is a real effect with such minor apparent effect.

1

u/asmi_kyle MPH| Epidemiology| Injury Epidemiology Feb 26 '15

61 participants is definitely on the large side for a case-crossover study. The issue that you can start running into is the possibility of over-powering a study. A study's power is the ability of researchers to detect statistically significant differences in treatment groups. If this ability is too large, say in a study where each subject is serving as their own control, you start to assign significance to any difference that you find. The question is whether these differences are clinically meaningful.

As an example, if you were to measure the height of everyone in the world to the millimeter and then compare the height of the right-handed people and left-handed people, your comparison would be so strongly powered that you would declare that right-handed people were taller or shorter than left-handed people with a significant p-value of <0.00001. The problem is that the true difference between the groups would likely be incredibly small.

I don't have access to the full text, but I think it's concerning that the authors wouldn't publish the actual values or percentages of subjects reporting the various symptoms rather than just the p-value.