A (11:08)
Andy and Jim have already given us a nice overview there. I think you can already sense the controversy here. You probably were aware of it before, but I think you've got a good understanding of why we're wrestling with this and trying to get this figured out as we think about the methods. I want to start with thinking about several related terms. As I mentioned in the introduction, we've not looked at a systematic review or meta analysis before, so we'll take a few minutes to explain that. First of all, just to make sure we're all on the same page. While these terms are often used together, they do refer to distinct things, and they don't always have to be done together. Systematic reviews in particular primarily focus on how you identify relevant articles. You don't have to do them with a meta analysis, and often they're standalone and they are very technical. So they describe in often excruciating detail, as they're supposed to, exactly how the authors went about searching for articles, what their criteria was, the criteria that they use to include articles in their review, how they assess the quality of these articles. So it's a very standardized. But the goal of that is if you read the way that the authors did it and then you redid it, you would find the exact same articles. A meta analysis is then sometimes done, not always, but sometimes, once you've done your systematic review, if the studies that are included are similar enough, they're asking the same question and reporting the outcomes in the same way, you have the ability to combine the results that data together. And that helps you in several ways. One way is that if you have studies that have discrepant results, if you can combine those, it maybe actually tells you what is the the correct answer, so to speak. Other benefits of it include if you're having a bunch of small studies and individually, there's not enough subjects in any one study for there to be statistical power to have a good conclusion. If you combine them together, maybe you have sufficient statistical power to be more confident in your conclusion about a result. So those are a couple of the benefits and reasons that people will do a meta analysis. The authors did several very sophisticated approaches here. One of them is a network meta analysis, and that's building on a basic meta analysis. And what a network meta analysis allows you to do is to compare multiple different interventions. Even when the included studies didn't compare them all together. So Andy already mentioned that we're looking at three different groups. We've got levothyroxine by itself, we've got combo T4 and T3. Then we've also got desiccated thyroid extract. Not all of these studies looked at all three of them. They looked at some combination of them. But network studies allow you to combine all of that together in actual networks so that you can compare one to the other in combination. Then finally, a meta regression is helpful in a meta analysis when you were trying to understand what might be a driver of an outcome. We're going to get to this, but there's a question always comes up, is this because of how much T3 you're using? This question of, well, did we over suppress somebody? Is this just because they've got a low TSH that's telling us that they've got more thyroid hormone than they need? So, so a meta regression is going to help you understand. Are there any drivers that you can identify like that? Okay, so that's a high level overview of these things as we think about this study. So this is a includes the eligibility criteria. It's the RCTs of both parallel and crossover studies that compared levothyroxine monotherapy with some form of combination therapy. Really quickly, a parallel study is going to take a bunch of people who are on levothyroxine and then randomize them to get either levothyroxine or some version of combination therapy. And then you're just going to compare those two, that you stay in those two groups, whichever one you were assigned to randomly, and you're blinded. Crossover studies are considered even stronger versions because you are initially assigned to get one of those treatments, levothyroxine or combined, and then halfway through the study, you are going to cross over and you are going to switch your treatment to the other one. You're not going to know as a subject, you're going to be blinded. You're going to know that you switched treatments, but you're not going to know which one you were on first and which one you were on second. But then that allows comparison with the same individuals. And so you don't have to worry at all about confounding there. And so that's considered a particularly strong design. And as we'll see here, the authors appropriately focus on that whenever there's any discrepancy. So those, any of those two designs were included here. The authors were only looking at adults with overt primary hypothyroidism and the outcomes, as Andy's told us, already had to include patient preference. And as before with these two different study designs, the, the crossover made sense because you were on both. And so at some point you were asked, did you like the first one you were on or the second one you don't know which one was which. Parallel studies are a little bit harder to think about, but primarily it's if you were on levothyroxine and then you got treated, they just asked the do you like this new thing that you're on or what you were on before? Again, it's not going to be as strong because these, not all these subjects were on both. And so that's yet another reason to why the authors excluded them as they did some of this analysis, to see if that made a difference. The authors state that they follow the PRISMA guidelines. So those are the standard guidelines for how to do systematic reviews and meta analysis. So they did that for their search strategy, their screening, their data extraction, the quality assessment, all the things that you're supposed to do. And the authors provide good details on that in the statistical analysis. There's a couple of important things that the authors do. There's a couple different ways that they dealt with data heterogeneity. So this is a very common thing when you're combining different studies. These studies are done in different ways. They're looking at different populations. Sometimes interventions can be a little bit different. There can be many different aspects to them and you get worried if you're combining studies that are very different from one another, if you're putting them all together, it's possible that the answer that you get is not really very well reflective of any of the individual studies. So one of the ways that you, you do that is when you're looking at the results, as you look at the spread of these results, you'll calculate both P values and I squared values. P values. We're used to thinking of, oh, you, you want a low P value that's good, that tells you that these groups are different. This is a little bit backwards is because you don't want your studies to be radically different. Your hope is, is that as you do a meta analysis, is that these studies are looking at the relatively similar populations that you're getting results that are, at least in the ballpark, you don't want them radically different. And so you are encouraged if your P values are relatively high that tell your groups are not wildly different from one another. The I square. The I stands for Inconsistency So that's the opposite. So you don't want a lot of inconsistency here. That's worrisome. So you get encouraged. If you have low I square values, one of the things that you can do is if you have data heterogeneity. So if your P values and your I squared values are telling you that your, your studies are fairly different and you maybe shouldn't be combining them, but you're not sure which studies are the ones that shouldn't be included, a visual way to do that is a funnel plot. You just graphically plot out where these studies go and you just plot them together based on how big they are and was the result favoring one or the other. And it actually should, as you put them on dots on a page, create a funnel. And as if you have studies where these dots are outside of this funnel, it just gives you a clue of, okay, that's probably a study that maybe doesn't fit very well, maybe you can tell why. And you say, oh, they have a totally different population. This does not at all fit with the rest of these studies. You maybe aren't able to readily identify what that is, but that's how you approach that, that the authors then, as I mentioned before, do a meta regression. So they're trying to understand what might be the driver here. So the things that they look at that might be a driver of different results that they're seeing with the levothyroxine monotherapy versus one of a combination. So they're looking at the dose of the T3, they're looking at the duration of follow up, the age of the subjects, the difference in the final body weight and the TSH difference. And in just a second, Andy's going to tell us about those results. Finally, we've alluded to this before, but to be clear, with this network meta analysis, there are three different nodes that are being looked at. So this is not just comparison of one treatment to another. You've got three different comparisons. You've got levothyroxine monotherapy, you've got combination therapy with separate pills for levothyroxine and lyothyrenine. And then finally you have desiccated thyroid extract. So those are your three nodes in that network meta analysis. A lot of information to be wrestling with here. Andy's going to walk us through some of these results and I'll turn it over to him.