HIV Vaccine!

[fls]

linda, your last statement may be backwards, 97% is the confidence that if the norm is 51 out of 8200, you can get 74 out of 8200.

Do you mean the probability of obtaining less than 74 out of 8200 if the norm is 51? That answer is also close to 97%, but that is not the number that I am referring to. My number represents the positive-predictive value - what is the probability that this positive result represents a true-positive?

Therefore, ineffective.

I don't understand how you are drawing this conclusion.

Another trial of 100,000 would bring the numbers closer together, showing how ineffective the inoculation actually is.

What do you mean by bringing the numbers closer together?

Linda

 

[ponderingturtle]

To expand on my comment above. Any Medical interventions can have a side effects and carry a risk. From the article some 7800 people were given 6 injections, that is nearly 47,000 injections. This appears to have prevented 19 people from developing HIV.

So you also look at how effective cancer treatments are over the entire population or only the percentage of people who get cancer?

Would you say that saying that the fatality rate of pancreatic cancer is .13%? After all saying that it is 95% is falsely looking at only the percent of people who get pancreatic cancer who die from it, not the total population.

 

[ponderingturtle]

80% was a hypothetical example. Here it appears to be about 1 in 110 (placebo) or 1 in 160 (treatment).

So if you could only cure 30% of pancreatic cancers it would be pointless because it is only a .04% difference after all.

 

[fls]

ok, with the new numbers the difference is .2806%

Lo, I said a bit off because you had a decimal place wrong

The point is, I can't believe anyone is taking this study as meaningful in any way! The expectation of getting one result when compared to another is highly likely, 98% if I am reading it right?

I'm not sure how you are reading it. The difference was statistically significant, in that the probability of obtaining those same results due to chance would be p<0.025 (my calculation - I don't know which statistical test they used).

What if it was a subject closer to many of your hearts?

Suppose I guessed the next card in a stack of 158 decks of cards. I got 51 right. Then I did the same thing, but this time with a Q-Ray bracelet on. Now I guessed 74 right. Anyone want to say that there is any effect at all from the bracelet?

Umm...you do realize that there is a difference between a sample size of 1 and 16000, right?

Linda

 

[Careyp74]

I'm not sure how you are reading it. The difference was statistically significant, in that the probability of obtaining those same results due to chance would be p<0.025 (my calculation - I don't know which statistical test they used).



Umm...you do realize that there is a difference between a sample size of 1 and 16000, right?

Linda

To clarify, I meant that I would guess the next card over and over again through all of the decks.

BTW, how did you compute that p value, against the population, or the placebos? I don't have a population value for getting HIV in high risk areas over a three year period ( I think that was the length of time) so I compared the two sides of the trail against each other. I didn't get any significance, I will do it again tonight with a TI-84 instead of Excel, I am not sure if I did it correctly.

 

[fls]

To clarify, I meant that I would guess the next card over and over again through all of the decks.

Right. But your n is still 1 as the comparison is between your guess rate with the bracelet and your guess rate without (i.e. your trials with the bracelet weren't independent from each other). ETA: I should note that the 'unit of sample' isn't always straightforward - depending upon the circumstances it can be individual trials, individuals, or a group of individuals.

BTW, how did you compute that p value, against the population, or the placebos? I don't have a population value for getting HIV in high risk areas over a three year period ( I think that was the length of time) so I compared the two sides of the trail against each other. I didn't get any significance, I will do it again tonight with a TI-84 instead of Excel, I am not sure if I did it correctly.

I did a Chi-square test.

I don't know what you mean by "two sides of the trail".

Linda

 

[Jorghnassen]

To clarify, I meant that I would guess the next card over and over again through all of the decks.

BTW, how did you compute that p value, against the population, or the placebos? I don't have a population value for getting HIV in high risk areas over a three year period ( I think that was the length of time) so I compared the two sides of the trail against each other. I didn't get any significance, I will do it again tonight with a TI-84 instead of Excel, I am not sure if I did it correctly.

You punched in the numbers wrong... z=(p1-p2)/sqrt(p*(1-p*)/n1+p*(1-p*)/n2), where p* is (n1*p1+n2*p2)/(n1+n2), and z is approximately standard normal. You can also use Poisson approximation, or direct binomial probability...

ETA: Or a 2x2 table and a [latex]$\chi^2[/latex] test as fls suggests.

ETA2: the latex stuff doesn't work well inline with regular text...

 

[fls]

You can also use Poisson approximation, or direct binomial probability...

Yes. I picked chi-square cuz all I had was the back of an envelope.

Linda

 

[Careyp74]

Right. But your n is still 1 as the comparison is between your guess rate with the bracelet and your guess rate without (i.e. your trials with the bracelet weren't independent from each other). ETA: I should note that the 'unit of sample' isn't always straightforward - depending upon the circumstances it can be individual trials, individuals, or a group of individuals.



I did a Chi-square test.

I don't know what you mean by "two sides of the trail".

Linda

Trial. it was a typo. There are two sides to the trial. The placebos, and the actual medicine receivers.

158 decks shuffled together is more than enough to satisfy the requirement for independence.

 

[fls]

Trial. it was a typo. There are two sides to the trial. The placebos, and the actual medicine receivers.

158 decks shuffled together is more than enough to satisfy the requirement for independence.

But whether or not you were wearing the bracelet for each trial was not independent. It's like counting each day in the vaccine trial as a separate sample, inflating the n to millions.

Linda

 

[Careyp74]

But whether or not you were wearing the bracelet for each trial was not independent. It's like counting each day in the vaccine trial as a separate sample, inflating the n to millions.

Linda

I don't follow, there are two stacks of cards, each containing 158 decks, the first stack is the control, without the bracelet, the second stack is the test with the bracelet. For each card in the stack, there is a guess, with a chance of being correct at 1/52. n is is 8216. How is n being inflated?

 

[jdp]

I don't think this is the sort of research which Beerina is looking for. After all, it will preferentially affect morbidity and mortality in the disenfranchised and the poor. Those are not the deaths she/he has displayed concern about.

Linda

I had read in another source that a parallel study was canceled in the US because neither of these two vaccines worked independently and this study was continued under some controversy. I also read that they were working with the general population and not particularly high risk individuals. With regard to the potential US study and what you noted above, am I correct in thinking that a US study (or indeed any in a low prevalence western country) would have to be absurdly large to generate enough events to be reliable? For example, I believe the rate of HIV infection in the US is about 60/100000 per year or so. A three year study then would probably need like 30 or 40,000 participants wouldn't it? Unless you restricted it to high risk people I suppose.

 

[Estellea]

According to this, it was a randomised, double-blind, placebo control trial.

 

[Eos of the Eons]

The woo woos are out being crude again. Some random negative comments from them:

http://www.cbc.ca/health/story/2009/09/24/hiv-aids-vaccine-thailand-study831.html

This is unbelievable! How was this article even published. First of all there was almost no background information on the control groups. And the 31% difference, are you kidding me!? How can this even be considered valid. The difference in 23 people not being infected with HIV in a group of over 8000 people. This means nothing. Were the people exposed to the same number of people infected with HIV or AIDS, or was it all left to chance. Also this test was done i'm assuming on only one race, which means that in the rest of the world it has no real relevance. The average person will read this article and think that we're on our way to finding a cure for HIV, when really there is no evidence here to prove that this is the case. Who the hell ran this study, this is a joke.


What's with all this vaccine pushing?
They really want the population to take their silly vaccinations.
I wonder why?
I wonder what is in those vaccinations?



This is very risky for a study and I believe some companies have to be prosecuted for what they are doing.
First, they pay a number of volonteers to go get infected and make up a story not to be prosecuted for it.
Second, they also pretend that the 2007 vaccine did not cause infection but it did increase the chances of getting HIV. It probably did not infect the patient directly, but I believe that the vaccine probably had some kind of mutation that ended up causing AIDS, unless a biochemist around here has a better explanation!
Third, race is also believed to be a factor in HIV infection even thought it has not been proven scientifically and Merck has never given the real reason end effects of its study in South Africa that was also discontinued: http://www.merck.com/newsroom/press_releases/research_and_development/2007_0921.html Once again, poor countries are being used as pigs in these experiments!

"Of all groups, those with HIV are the very last that might benefit from the further immunosuppressive effects of vaccines. "

I think most of the people making these comments in this section are Canadian. I am happy to see some people making more intelligent comments there as well.

 

[fls]

I don't follow, there are two stacks of cards, each containing 158 decks, the first stack is the control, without the bracelet, the second stack is the test with the bracelet. For each card in the stack, there is a guess, with a chance of being correct at 1/52. n is is 8216. How is n being inflated?

A trial, measuring the effectiveness of an intervention will involve a number of subjects and a measure associated with each subject. In the case of the vaccine trial, the measure associated with each subject was the presence or absence of HIV. In the case of your Q-ray trial, the measure associated with each subject was the number of correct guesses. The number of subjects in the vaccine trial was 16000. The number of subjects in your trial was 1 (maybe 2, depending upon how the data is analyzed). The sample unit is not the individual guesses. Measuring the same person 50 times is not the same as measuring 50 people once. It merely represents taking a more precise measurement. That is the first problem with your scenario.

The second problem with your scenario is pre-test probability. The pre-test probability for the vaccine trial - an adequately powered randomized controlled trial with prior research demonstrating plausibility - is 0.50. The pre-test probability for the Q-ray bracelet - discovery oriented exploratory research - is 0.001. This means that instead of being 97% confident in the results, you are less than 4% confident that the results represent a true-positive.

Linda

 

[fls]

I had read in another source that a parallel study was canceled in the US because neither of these two vaccines worked independently and this study was continued under some controversy. I also read that they were working with the general population and not particularly high risk individuals. With regard to the potential US study and what you noted above, am I correct in thinking that a US study (or indeed any in a low prevalence western country) would have to be absurdly large to generate enough events to be reliable? For example, I believe the rate of HIV infection in the US is about 60/100000 per year or so. A three year study then would probably need like 30 or 40,000 participants wouldn't it?

Yeah. Especially when you take into account dropouts and the lower incidence usually found in research samples.

Unless you restricted it to high risk people I suppose.

Yeah. At which point you will be accused of taking advantage of disadvantaged people by making them guinea pigs in your experiments.

Linda

 

[Eos of the Eons]

Yeah. At which point you will be accused of taking advantage of disadvantaged people by making them guinea pigs in your experiments.

Linda

Precisely.

 

[Kahalachan]

Is this being administered or is this just a breakthrough?

I worry with such a low success rate, that if administering it will just help HIV evolve as opposed to a more efficient vaccine that nearly wipes it all out.

 

[LostAngeles]

I think so. Tell everyone to assume that they are not protected and take reasonable protections. It's not worse than not participating in the trial at all.

According to the report I read, both groups were given condoms and information on safe sex. They knew what the trial was for. Those that were infected are getting their anti-viral drugs.

Is this being administered or is this just a breakthrough?

I worry with such a low success rate, that if administering it will just help HIV evolve as opposed to a more efficient vaccine that nearly wipes it all out.

It's a breakthrough. The two vaccines used were ineffective in earlier trials on their own. This one combined the two.

 

[Careyp74]

A trial, measuring the effectiveness of an intervention will involve a number of subjects and a measure associated with each subject. In the case of the vaccine trial, the measure associated with each subject was the presence or absence of HIV. In the case of your Q-ray trial, the measure associated with each subject was the number of correct guesses. The number of subjects in the vaccine trial was 16000. The number of subjects in your trial was 1 (maybe 2, depending upon how the data is analyzed). The sample unit is not the individual guesses. Measuring the same person 50 times is not the same as measuring 50 people once. It merely represents taking a more precise measurement. That is the first problem with your scenario.

The second problem with your scenario is pre-test probability. The pre-test probability for the vaccine trial - an adequately powered randomized controlled trial with prior research demonstrating plausibility - is 0.50. The pre-test probability for the Q-ray bracelet - discovery oriented exploratory research - is 0.001. This means that instead of being 97% confident in the results, you are less than 4% confident that the results represent a true-positive.

Linda

When figuring out the confidence interval of expected results based on, say, 95% confidence (doesn't matter but let's just use that level) you are going to use the same numbers from my example as in yours. n is not 1, it is 8216. It doesn't matter that it is one person doing the test, just like it doesn't matter if it is one person that flips a coin 10 times, or 10 people flipping a coin once each.