Clinical trials & medical research (young people)

Understanding allocation (randomisation) to a treatment comparison group

In some trials (especially Phase 1 and Phase 2 trials) everyone taking part will get the treatment being evaluated. (See also 'Why do we have clinical trials in children and young people?’) However, many trials compare a new treatment with the standard or usual treatment by allocating people to two groups. People allocated to one group (the experimental group) are given the new treatment. Those in the other group, called the control group, are given a standard or existing treatment. If no standard treatment exists, the control group may not be given any specific treatment or may be given a placebo. Some trials compare more than two groups, perhaps comparing a new treatment with two or more well-established treatments. (Sometimes you may hear the experimental group called the ‘trial group’ or ‘intervention group’. This can be confusing, as all the groups, including the control group, are part of the trial, and people in the control group may also be given an intervention, in the form of the standard treatment).

Kay took part in her first clinical trial two years ago. The aim of the trial was to test improved medicines for the treatment of cystic fibrosis.

It can be scary not knowing which drug you are taking, but it is a chance Kay wanted to take if...

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Age at interview: 23

Sex: Female

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At the start of the Mannitol study it was kind of double blind exercise so the doctor didn’t know if I was on Mannitol or it was a placebo and I didn’t know.

And did it, what, you’ve explained about it being double blind and placebo can you tell me a little bit more about that and - because you didn’t know at the time?

No, to begin with they said, I think it’s one in four chances that it could not be the Mannitol drug. So one of them, so I think three would be the Mannitol, but they’d be different strengths and the one would be a placebo so it would be, it wouldn’t have any kind of clinical effect. So they said, you know, there is a possibility that you might not be on the drug but if you feel worse or you feel like you want to drop out at any time during the study, you’re more than, you know, you can. So I think if I felt that I was getting any worse I would have probably thought that I was, I was on the placebo, and I probably would have dropped out to be honest. But it’s quite a scary thing to think you’re trying something that you think is going to help but it might be a placebo but I suppose you need to take that risk sometimes if it’s going to improve your health.

So that’s what I was wondering, because, if you don’t know what you’re having, at what point do you think, or was there a point because you were feeling better so you kind of in your mind think “Oh I must be on....” Did they actually inform you at any stage?

I’m free to ask, it was I think it was after the twelve months you can find out and I think the nurse did tell me that I was on it as soon as I asked really. The information’s available after the twelve months I think or it might be the sixth month, but yeah, you were able to get the information after you’ve completed a certain phase.

Kay doesn't think that she was on the placebo because of the way she reacted.

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Age at interview: 23

Sex: Female

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The way I reacted to the to the drug that I was in inhaling, because the Mannitol was actually in a little capsule like you pierced and then you breathed in. And the way I reacted to the to the drug or the placebo of Mannitol, I thought I was on some kind of drug because it really helped me bring up the mucus on my lungs.

Do you think if you’d been in the placebo, if you’d have found out you’d have been in the placebo group would you have been disappointed or? I mean the fact that you knew...

I don’t know

...the fact that you knew that you were in it, you kept going, but if you kind of thought...

I don’t know.

..it’s a bit you know like a hypothetical question because it didn’t happen but...?

Yeah, well I think the doctor said, “Even if you’re on the placebo you, because it’s such, because it’s an inhaled drug it has some kind of effect on your lungs anyway, so it might not be the Mannitol, but it might cause some kind of, not allergic reaction but reaction for you to cough so you probably would cough up something anyway”. So, although it was a placebo and it wasn’t Mannitol you’d probably get some kind of reaction anyway.So, the way I acted towards it, I think I was on Mannitol but I could possibly have been on the placebo. But because I reacted so well anyway I don’t know my lung function went up, that was what I wanted really.

Soon after Kay completed her first trial she was invited to take part in a similar trial for a different medicine. Because of the success of the first trial, she was keen to take part, but she had to leave a gap between completing one trial and starting another. (See ‘Different types of trials’ and ‘What is involved in a trial: appointments and monitoring’.)

To make sure that each group contains a similar mix of people, many trials are ‘randomised’. This means that people are allocated at random to one of the comparison groups in the trial, often by using a computer programme. When people are randomised they have an equal chance of being in either trial group. Random allocation helps ensure that two very similar groups of patients will be compared, so if one group does better than another, it is likely to be because the treatments being compared have different effects, and not because of differences between the people in the groups. The UK Clinical Research Collaboration booklet on ‘Understanding Clinical Trials’ explains these and other terms.

Hannah, aged 17, took part in a randomised trial comparing different approaches to giving information to young people with diabetes. She had to complete two questionnaires asking about visits to the doctors, what information she received, and questions about diabetes. She says she was allocated to the control group.

Being randomised makes it a fair chance of being in either trial group. Hannah was happy to be in...

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Age at interview: 17

Sex: Female

Age at diagnosis: 4

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Just like maybe a computer system selecting just random people off a list in to the group. So it doesn’t, no one’s been selected for any reason, just they’ve been put in to that group and not really any reason for it.

And you mentioned about, that you were a control?

Yes.

What does that mean?

Where I don’t get any of the new information. I am just, carry on as normal, use what the dieticians have already gave me, don’t change anything that I do. Because that means I, they’ll then compare me to the experiment group where they get given new information.

So you you were just having…

Yes.

…the normal…?

I didn’t have to change anything, no.

And were you happy with that…

Yes.

…you were in?

Yes. I would have been, like interested to see what the other things was as well, because, yes, it’s been a very long time since I was given all my sheets and, explaining like all my diabetic…Because it would be nice to know again what like I need to go over, because I was only like 4 when I was diagnosed. So I obviously wasn’t the one reading through all the information packages. It would have been my mum and dad.

If no standard treatment is available, the control group may not be given any specific treatment, or may be given a placebo. A placebo is a treatment with no active ingredient, which is designed to appear very like the treatment being tested. By comparing people’s responses to the placebo and to the active treatment being tested, researchers can tell whether the treatment is having any effect in addition to the effect of feeling better because ‘something is being done’.

There are several ways in which the results of trials can be made as reliable and accurate as possible. One of these is to make the trial a ‘blind trial’. In a blind trial the participants are not told which group they are in. This is because, if they knew which treatment they were getting, it might influence how they felt or reported their symptoms. Some trials are double-blind, which means that neither participants nor the doctors and others treating them know which people are getting which treatments. This also avoids the doctors’ hopes and expectations influencing the results of the trial.

Helena, a health professional has a lot of experience of clinical trials and explains what some...

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Yes some terms that we use are blinded which means that you don’t know what treatment is, the patient’s having. There is single blinded where just the family don’t know, double blinded where the family and the researchers at site don’t know. Randomised means where a patient is randomly allocated one arm of the treatment of the study or another. And there can be two arms to the treatment, there can be three arms and they are randomly allocated. There are lots of different ways that they do like and how they’ll be done electronically or it can be done by sending a fax and someone not related to the study, here at site, randomises them and picks the next consecutive envelope, as simple as that or enters it onto a spreadsheet and it randomly allocates them.

Placebo, there’s some studies what we call placebo controlled and some patients get a placebo. A lot of families like it explained as a dummy drug so it’s a drug that isn’t a drug. It can be a lactose tablet or something else. And it will always be made to look exactly the same as the actual active drug so that people don’t know. So if we had a girl and a boy both on the study they couldn’t look at the drug and say, “Oh well you’re on different than me”. They would always look the same and the tablets would look the same as each other, liquid would look the same as each other and everything would look the same as each other. And the idea of a placebo is it that the active ingredient is helping the patient and the symptoms and the quality of life or is the fact that they feel that having something is helping them and that’s, it’s very interesting to see the placebo effect.

Some young people were told by doctors that being randomised was like a ‘lottery draw’, or being drawn ‘out of a hat’. Others were unsure about randomisation, and some found it difficult to explain. Often people knew they would prefer to be in one arm or the other. Joe was pleased to be allocated to the new intervention.

Joe took part in a randomised trial comparing different approaches to helping young people newly...

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Age at interview: 15

Sex: Male

Age at diagnosis: 15

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Well, they explained what they were going to do in the trial. They explained like about diabetes. And they said, “The trial is just to see how you cope with, with like, with diabetes.” And in hospital I think it w-, it was better because if I needed any, if I had any questions I could have asked them and stuff. But I think if it, if I had the trial at home I would have been able to like, you know, deal with it on my own more, instead of like asking people.

So was there a choice?

No. The organisers, they choose for you.

I was going to say, I was wondering whether you were randomised. And did, and did they mention about the, explain about the, that grouping in those groups to you?

Yes, they, they said, they mentioned that they wanted to see how people dealt with it in different like situations. Like when I was in hospital, if like, you know, at home, to see how people coped with it more. If you got put in hospital it was just for the doctors to help you really and stuff.

If you’d have been in the other group, how would you have felt?

I think I would have been a bit more worried because it was a complete new thing. It wasn’t, like no one in my family has got diabetes and we didn’t know anything about it. And if I’d got sent home to the other, it would have been like much harder, because if you get stuck on, like on something, you can’t ask. I mean they had, they give you numbers to ring up and stuff, but you can’t like immediately ask and stuff. So I think the hospital was much easier to deal with.

So you were quite pleased about that?

Yes.

I just wondered like in the term randomisation, how you would explain that? Because that’s what happened?

I’m not, I’m not really sure about that. They just said just to see how people deal with, and just completely random.

Randomised trials are done when we don’t know which treatment is best, in other words when the relative merits and disadvantages of different treatments are uncertain. It is important to realise that, on average, new treatments are as likely to turn out worse as they are to turn out better than existing treatments. This means that, going into a trial, everyone, regardless of which of the treatment groups the computer allocates them to, must have similar chances of a good outcome. If people would strongly prefer one of the treatments being compared, they should not volunteer for the trial.

Mohini decided not to take part in a trial after a lot of discussion with the consultant and her parents, because she really wanted the standard treatment. (See also ‘Deciding not to take part although eligible to take part in a clinical trial’.)

Mohini thought randomisation was quite a risky strategy, but once the consultant explained it,...

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Age at interview: 12

Sex: Female

Age at diagnosis: 9

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And then he said that we’re doing the trial, you’ll be put in something called randomisation and you‘ll have either one block or two, basically.

So when they said you were going to be randomised, what does that mean to you, what did you understand about that?

He explained it as you’re put in a computer and the computer decides yes or no from that they say one block or two.

And did that....

And it was really weird, I imagined this black and green screen with all those names like going [sound of fruit machine], it sounds really stupid but that’s the first thought that came to my mind when I thought of it, I don’t know why.

No.

It was a bit like one of those thingy machines.

Three cherries is it? Or three oranges.

That’s the thought that came into my mind surprisingly.

Because it’s just, you know...

Random, it is random.

What’s going to go where?

Yes.

So you understood about being randomised.

I think I understood randomisation.

If you had to explain it now to another young person what that meant, how would you describe randomisation?

I would describe randomisation as basically it’s almost like your name is being picked out of a hat to put it simply. And it is just pure luck if you want to call it luck. It is just either you’re picked or you’re not. I don’t know it’s really difficult because like I’ve been with MCRN for ages so I know all the technical terms and how to explain them technically but sort of what I know now so back to that level a little bit difficult.

Yes. And how did that I mean at the time but how did you feel about that, you know, you were going to be randomised, have one treatment or the other treatment without knowing?

I thought it was quite a risky strategy.

Why’s that?

Because you don’t know what’s going to happen, you’re saying yes to a trial but you’re not guaranteed to have one block so you’re basically taking the risk that you might have signed all these forms and said yes and then do what you would have done anyway.

I mean and in terms of being allocated to a group how does that feel when you’re going to be allocated to a group when you’re going into one or the other?

I think it is quite a scary prospect because you are just being randomly picked but I think once they explain it it’s fun, it’s pretty simple to understand it’s like blue cube, blue cube, orange cube, blue cube, yellow cube we do that like do you know like yes, it’s a really weird way of explaining it.

Dr William van't Hoff explains about the importance of randomised trials.

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In many studies, in many trials or studies of medicines, part of the proper practice is that the participants, in this case children are not aware whether they’re taking the new medicine or perhaps a dummy medicine called placebo or another medicine. Because if they were aware or their doctors were aware which one they were taking, this might influence the results and give a false answer, which none of us want. And so in many trials like this the term blinding is used and this refers to the patients, the families and/or doctors not knowing which of the medicines the child is on. Is it the new medicine or is it the comparator medicine? Now these are very useful and, and in a way the gold standard to provide the best research answer. But thereafter longer-term studies can be done when the medicine is known to the family and to the doctor. This is a, a, a phase of a trial that we call open-label, in which they are aware which medicine they’re having and may continue to take a medicine if it’s been shown to have a benefit.

There are several ways in which the results of trials can be made as reliable and accurate as possible. One of these is to make the trial a ‘blind trial’. In a blind trial the participants are not told which group they are in. This is because if they knew which treatment they were getting, it might influence how they felt or reported their symptoms. Some trials are double-blind, which means that neither participants nor the doctors and others treating them know which people are getting which treatments. This also avoids the doctors’ hopes and expectations influencing the results of the trial.

If no standard treatment is available, the control group may not be given any specific treatment, or may be given a placebo. A placebo is a treatment with no active ingredient, which is designed to appear very like the treatment being tested. By comparing people’s responses to the placebo and to the treatment being tested, researchers can tell whether the active treatment is having any real effect in addition to the effect of feeling better because ‘something is being done’.

Some young people we talked to took part in randomised double-blinded placebo controlled trials. This means that young people were allocated randomly to one of the trial groups and neither young people nor doctors or others involved in their care knew which group they were in. For some young people this was quite a scary thought.

Toby, aged 11, took part in a randomised placebo controlled trial of treatment for migraine in children. He explains a double-blinded trial as “Only the people (pharmacy) that shuffled them up (the pills) and gave them to me know, like the doctors and nurses didn’t”.

A placebo is like a 'mint' or 'sugar and water', says Toby.

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Age at interview: 11

Sex: Male

Age at diagnosis: 6

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So how did they tell you what randomisation means?

Like out of so many different pills they like shuffle them all up and grab one and then it like they gave it me and then they done that to everybody else that’s inside the trial.

Right okay so that’s how he explained it?

Yes.

Did they use words like control group and or placebo?

Placebo yes.Because a placebo inside the like the medication a placebo’s one of them.

Okay. And can you tell me what you understand by a placebo?

It means it’s basically, say out of the actual drugs and, it means it’s like basically just a mint, say something like that because it don’t really mean anything it’s just like sugar and water basically, that’s it.

Some young people described placebo as a ‘dummy’, ‘fake’ or a ‘blank’ drug and not the actual medicine.

Taking part in double-blinded trials and not knowing which drug you are taking can feel a little ...

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Age at interview: 18

Sex: Male

Age at diagnosis: 16

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What, can you tell me what your understanding is of those terms?

Randomisation. It just means like if there’s three people on the trial, one of them may be on the placebo and two of them will be okay. Or any other way. It could be 50'50 or 25'75. It, any order it can be. One person may have it, two people may have it. So it’s randomisation on that one patient. And it’s a double blind, so even the doctors don’t know. You don’t know and the doctors don’t know. So only the people who know it are the people who are making the drug and the drug trial people. That’s what I know about the randomisation. The placebo just means it’s not the drug. It can be sugar water for all we know, or aspirin. We really don’t know.

And did you mind that part?

It was weird, in my opinion, because you’re kind of sitting there going, “Well, am I? Aren’t I? Am I? Aren’t I? Am I just being ill? Or what’s going on?” So it was a bit worrying on that one, but you do kind of come to the fact that you think, “Oh, okay.” You do have to learn to deal with this bit because it’s part of, part of, well; it’s the point of the drug trial, to see if this drug actually works or if it doesn’t.

Does it worry you that, the fact that it, the doctors don’t know either?

The doctors don’t know, but your bloods will show it, won’t they? Well, they’re supposed to. Mine actually didn’t. But they’re supposed to. So if anything does really come out they have the ability to have to go, “No, we need to see it now.”

And have they told you at all when they might open it up to let you know if you’ve been on the placebo or not?

I don’t think I ever will be able to know, because the doctors still don’t know if I’m on it or was I on it or wasn’t I on it. I, I’m pretty sure I was because of the pain it felt in getting injected in and how it, how I felt in general. But I still don’t know ever, if ever I will.

Do you, would you want to know though?

It wouldn’t be bad to know. It wouldn’t really change much though, would it? So it would be interesting, but nothing would really change from hearing yea or nay on it.

Jenna aged 13 was diagnosed with polyarticular idiopathic arthritis at the age of 11 and is taking part in a double-blinded trial. The trial is a three year trial and Jenna has been taking part for one year so far. She attends the hospital once a month to receive the treatment which involves being on a day ward to receive the ‘drug’ or the ‘placebo’. She explains randomisation as; “It’s where they just sort of randomly put people in different groups to sort of make it fair”.

Jenna was worried about the possibility of being allocated to receive the placebo in case her...

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Age at interview: 13

Sex: Female

Age at diagnosis: 11

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So what happened at the beginning then? Tell me about that.

I think I went like every two weeks for a blood test and then for the thingy. And sometimes I had to go in every week at one point. And so it changed. And there was like a blind part of the trial where you didn’t know if you were getting like a placebo, like a fake one, or the real one, to see if it was just sort of like in the mind that you, it was working or if it actually was working.

And do you know what you were on?

Not yet, no. Because it, I’ve finished the blind part but they haven’t told me yet.

So you, you’ve finished that part but they still haven’t, are, are they going to tell you?

Yes. They need to find the paperwork with it on I think.

How did you, when you signed up and they said, they probably said to you, “This is a

randomised placebo controlled trial” did they mention that in the information you had?

Yes, they like went through all the stages in it and saying like there’ll be a blind part and then there’ll be like fasting ones, and like told you everything you had to do.

And what do you understand about randomisation and placebo?

Yes.

What, how can you, if you were to explain it to somebody, how would you explain it?

Well, a placebo is like a fake one that doesn’t really do anything. And like it just sort of, like it just sort of is like random and you don’t know what’s happening really in some parts of it.

And how did you feel, that you might be on a placebo?

Worried, because it might like flare up. But it didn’t. So I think I was on the real one.

It is a bit of a worry when you don’t know what’s, what you’re having. Do the doctors know what they’re having?

Mum' No, nobody knows.

So they call that sometimes double blind, when even the doctors don’t know. So did that worry you at all?

Not really, because like I’m sure they could find out if they really needed to, if it was an emergency.

They said that you can escape. If she started flaring up then they would automatically put her back on to the real thing. So if, if anything did happen in the blind part you just come out of it and back in to the normal drug.

The normal treatment or the usual treatment…

Yes.

…that you were having?So they were monitoring, so if something happened did you have a number that you could ring up?

R' [um] I think we would just ring the hospital if something happened.

Ryan, aged 12, was also a little worried that the doctors didn’t know what drug he would be taking in case his arthritis starting hurting again.

In the second stage of the trial, Ryan was allocated to a treatment comparison group and neither...

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Age at interview: 12

Sex: Male

Age at diagnosis: 8

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And when they said you could take part, were you quite pleased?

Yes, because I didn’t want to have the needles anymore because it was making me angry at my mum a lot and it was making me a bit sad as well.

Was it?

So then when I had it, it just, it, because they told me it would just be for a wee-, few week, weeks, for a few times until the second period of it. But then I’ve been on to a blind stage which is whether I’m not having it or I am having the actual drug. And that’s where I am now. But it’s a bit better, but I know I don’t know it, but

You feel better? So when, that’s interesting, that they explained to you that you, there were different groups and that you would, so did you have the, they say you would have the drug to start with?

Yes, and then I go on to, which, period two, which is like the blind stage, which I don’t know which. But if I got really, if I get really bad then it’ll just go open and they’ll put me on a drug.

What did you under-, when they said that, do you know what they mean by blind?

I didn’t know at the start, but they told me it was like where they, where I was either having it, I might not be actually having the drug but it weren’t anything that would harm me. It was just I think water or something in it.

And did they mention the word randomisation to you?

Yes.

What did they say about that? Can you remember?

In the blind stage that’s what they basically said; randomised between, between like I get or I don’t. So they’re not sure, they’re not sure themselves. Only the drug company knows.

So the doctors don’t know which one? So that, sometimes they call that double blind, where you don’t know and the doctors don’t know.

Yes.

Does that bother you at all being in, you don’t know?

A bit. Because I, I feel like I want to ask questions about it, but there’s no one knows about it.

So what sort of questions do you want to ask?

Like just what, what does the what does it do basically? How does it work? And how do they make it? And am I actually on the drug at this stage or not?

It’s those things you want to know?

Yes.

Do you think, will there be a point when they will tell you?

I think so. I’m not sure.

They’re questions that you should be asking?

Yes.

Do you think you’ll ask when you go again?

I don’t know, because the doctors there don’t know.

It might just help them to explain it again to you and go through it again? The fact that you didn’t know the doctors very well and that and you took part, did that worry you at all, you know, because you didn’t know them?

Yes.

In what way did that?

It just worries me because, I worry, I’m worried if I start getting really ill and then it just started hurting again.

And then, just tell me what happened there.

The next stage, it was, it was every month. And I’m still on that stage. But we’re not sure if it’s, we think it’s the drug but it, we’re not sure.

What makes you think it might be the drug you, that you’re still on?

Because I’m not getting, basically I’m not flaring up. Like my knees aren’t going up or anything. So it&rsq

Sometimes when people do not experience a change in symptoms they assume they must be taking the placebo. However, this is not necessarily the case, as not all drugs work on all patients in the same way. Equally, people who are taking a placebo may sometimes experience improvements in their health. This is known as the placebo effect or placebo response. We still do not understand exactly why this happens, but it seems that believing a treatment will help can result in real changes. This is why new drugs are often compared against a placebo – if the patients on the drug do significantly better than those taking the placebo, it suggests the new drug has an important additional effect. If people were only given the new drug, we could not be sure if improvements were simply due to a placebo effect.

Robert was diagnosed with cystic fibrosis at birth. He has taken part in various trials since childhood. When he was 14 he took part in a randomised placebo controlled trial to assess whether a steroid used for people with asthma helped people with cystic fibrosis.

Having a computer to randomly allocate you to a group makes the trial fair. Robert was allocated...

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And these are all clinical trials to do with cystic fibrosis and helping other people?

Yes and I’ve and, you know, sometimes I have seen a direct benefit from it, almost. I took part in one study where it was assessing whether a particular steroid flixotide, whether, it was assessing, it was known to have a good beneficial effect in people with asthma but it wasn’t really known if it was for people with Cystic Fibrosis. And as it happened in that trial I was on the placebo and there was no change so as a result of taking part in that trial I was able to come off a steroid that I was on effectively needlessly. So I have seen direct benefits in that way but then also sometimes it’s longer term like the one I’ve just told you about with the dripping through the nose because that’s run by one of the doctors at the hospital and I’ve seen him subsequently and he said “Oh yes we actually found some good results and it’s been written up in a paper and it should end up in a journal”. So it’s nice to know that what I’ve taken part in has worked and it is making progress.

Okay and what do you understand by the terms like you mentioned double blind and placebo, what do you understand?

So placebo is where, well in a, in a double blind trial which is where no one not even the doctor running the trial knows which person is actually taking the drug and which person is just taking an inert substance and, which is the placebo. Because it’s not actually the drug but everyone thinks that they might be taking the drug and so that means that you could see, you’ve got some people actually on the drug and some people not actually on the drug and you can make a direct comparison. And because no one knows who is on which then, then that makes it a fair trial.

And did you know did you have any idea when you were going through what you were on?

No I didn’t, no. I hoped I was on the placebo because then I might get to come off the steroids [laughter]. And as I say not even the doctor running the trial knew. I think they’d got a computer to randomly generate it and then you know, it tells them how this person has to have inhaler number 234 and then you only find out afterwards whether you are on the placebo or not but at the time no one knows.

Some of the young people we talked to were pleased they didn’t know which drug they would be taking as Katie explains.

Katie was pleased not to know which drug she was taking, she may have tried harder to be better...

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Age at interview: 13

Sex: Female

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And did they use words like randomisation and placebo and?

Yes because one of the medicines was a placebo and one of them was the actual medicine.

Okay. And what does placebo mean to you?

It means it’s not an actual medicine it’s just a dummy or something.

Were you randomised into a group, did they say you’d be randomised?

Yes.

How would you explain that to somebody?

That you don’t know which one you’re going to get first and which one you’re going to get second.

Right and were you okay with that?

Yes.

Yes, how did it feel like to be sort of not know whether you were going to get the actual or?

It was everything like you just want to know but in other ways you don’t. You want it to be a secret or a surprise.

Why is that?

It’s just because it’s nice to not know sometimes because you don’t want to know you’re just taking something that isn’t the actual medicine and yes.

Do you think if you’d have known, then if you were taking the placebo perhaps you might have...?

Yes, because I would have tried harder to be better probably. Or said stuff that make it sound like I was better. Even though I knew I was on the medicine.

A lot of the terms used in trials are quite complex and closely related to each other. Below are some brief definitions as a reminder of how they fit together. For help understanding these terms see links to further information in our Medical reseach resources.

Control group – a comparison group in which people often get a standard treatment. If no standard treatment exists the control group receives no specific treatment or a Placebo.

Randomisation – allocating people at random to one group or another, so that each group contains a similar mix of people. Random allocation helps ensure two very similar groups of patients will be compared, so if one group does better than another, it is very likely to be because the treatments being compared have different effects, and not because of differences between the people in the groups.

Placebo – is a treatment with no active ingredient which is designed to appear very similar to a supposedly active treatment with which it is being compared. By comparing people’s responses to the placebo and to the treatment being tested, researchers can tell whether the treatment provides any additional benefit.

Double blind – trying to ensure neither patients nor doctors or others treating people in a clinical trial know which treatment each person is getting, so that this knowledge does not influence how patients feel or how doctors interact with their patients or interpret the results.

For more information, see our resources page.

Last reviewed March 2017.