[aristus]

Iirc it was 26 animals total. I read the paper when the blogosphere was hyperventilating about it. The data looked very shaky. If they had stopped a few months earlier they could have concluded that gmo maize prevents cancer. Way too small a population, in other words.

[rainforest]

According to §2.3, there were 200 (100 of each sex)[1]. These 200 were divided into groups of 10. One group per sex was control (standard feed, water), 6 per sex had different amounts of GMO food and 3 per sex had normal feed + Roundup-treated water.

I don't feel confident attempting to interpret or criticise the results, but I did notice there weren't any null hypothesis tests; could anyone with more experience in biostatistics say whether or not their analysis is the norm?

[1] : http://www.sciencedirect.com/science/article/pii/S0278691512...

[tedunangst]

There are some weird results in there. Table 2 has the results for males in a format that's pretty easy to eyeball.

The pituitary results are particularly weird. The more GMO you eat, the fewer anomalies you have. The more Roundup you drink, the fewer anomalies you have. Actually, that last comment holds true for every category in the last three (R) groups. Drinking Roundup is always worse than the control group, but the more Roundup you drink the closer to the control group the results become.

[1337biz]

Aren't even medical trials having most of the time not a much larger sample size than 20-50 participants?

[Sanddancer]

Depends on the test. Full-life trials, like this one, tend to have many more than that because you need to take into consideration a lot of the random factors of being alive. However, there other things to keep in mind here. The breed of rat used has a predisposition to get cancer in a real short time; more than half of Sprague-Dawley rats will get cancer within two years. As a result, they're used much more often in research centered around having cancer than getting cancer. Finally, the rats were allowed to eat food whenever they wanted, and however much they wanted. So, there's the possibility that one or more of the groups through chance just had particularly gluttonous rats. Because of this, you have a lot of questions as to what could have led to the problem -- was it the GMO corn/roundup, or did the rats feeding on GMO/Roundup corn eat more, or was it just (un)luck of the draw, etc?

[bayesianhorse]

One big difference is the cost of the studies. A study with 20-50 human participants would be orders of magnitudes more expensive than using rats.

But there just is no practical reason why this particular study lacks a control group or the statistical power to show its conclusion.

[jules]

Actually, in many countries it is really really hard to be allowed to do a study on a significant amount of animals due to animal rights groups, which have lobbied for committees who decide how many animals are allowed. Most times this number is way too low to do good science (numbers like 16 -- 8 main and 8 control mice, are not uncommon).

[grammaton]

Some studies that purport to show certain effects do, and are routinely criticized for the same reason. Proper medical trials, particularly for, say, a new drug use far larger sample sizes.