A cohort study is a type of medical research study. it’s different to a randomised trial which is, in which people may be given a drug or type of intervention and it’s more of a long-term study where you’re just following a group of participants for a long time. it’s particularly useful to find out risk factors for certain, developing certain diseases and often you want to follow the people until an outcome occurs and this may be developing a disease, it may be dying, so you may be following people up for life or it may be something else.

A cohort study will follow people up and be looking more at risk factors for, for developing a disease. So, for example, you may want to work out if smoking causes cancer and this can’t really be done in any kind of other study design, you can’t ask people to start smoking so you can see what effect this has.

So you’ll follow up a group of people and compare people who smoke with those who don’t smoke and look at their outcomes long-term and those outcomes, because they’re likely to be health outcomes like developing cancer or respiratory illness or dying means that you’ll have to follow those people up for a long time.

I would say that their participation is really valuable however they need to be aware that there will be a time commitment from their perspective and they’re unlikely to benefit directly in many cases. They have to attend study visits which, which means they’re having a lot of tests done so their, their doctor or nurse may pick something up that they wouldn’t otherwise have picked up so they may feel that there’s, there’s extra care going on but overall the cohorts study is to change, you know, our understanding for people in the future rather than the people who are participating.

So the reason that cohort studies are important is that they can answer health questions which you couldn’t answer in another way. So, for example, the study I work on, chronic kidney disease, you can’t do a randomised trial of whether chronic kidney disease gives you results in dialysis or results in cardiovascular health problems.

So you have to just follow up a population and look within that population at what other risk factors they may have, which then may make them more likely to go onto develop long-term health problems or cardiovascular disease. So, and similarly with smoking, you can’t ask some people to smoke and not to smoke, so you take a population, find out who smokes, who doesn’t smoke and follow them both simultaneously, and that could apply to a lot of things, that could apply to weight or other lifestyle dietary issues, dietary behaviours. To, yeah, long-term find out how this affects their health outcomes.

So, this is one of the downsides of being a participant in a cohort study, is that if it’s long term health outcomes it’s going to be a long time before you hear anything. Part of the reason for this is the outcomes are actually not occurring for many years, but another part is that you can’t really feedback too much to the patients until they’ve had, until the paper, until the work has been published and seen by the scientific community and approved by a journal. So that can take a long, long time.

We do try to give newsletters saying, you know, feeding back that participation is, the participants contribution is really valuable and we value it and we want them to keep going. And then obviously when we do have results that are published, we’ll try and present those in a format which is meaningful to the participants, the study participants so that they understand exactly what we have done and why we have done it.

Yes there are-, cohort studies can be prospective or retrospective generally and a prospective study means that you recruit a group of people who consent to be in the study and you follow that group up over time you collect data throughout the follow up generally, I mean sometimes you’ll just collect data at baseline and then follow them up, found out what their outcomes are longer term but you may want to do annual follow ups where you give people questionnaires to find out about their lifestyles, to find out about their smoking habits whether they’ve developed other illnesses, take some measurements, potentially find out their weight and height so you can get their BMI, find out if they smoke, find out if they’ve got another disease which may affect your outcome. A retrospective cohorts study is the other possibility and that’s using generally a dataset that already exists so you already have all the data that you need and you don’t need that long term follow up because it may be hospital records, it may be GP records and you can look at similarly a group of participants, for example, a group of people with and without diabetes and do some of them go on to develop more complicated health problems, but you’ve got all that in the records already. So, you’re doing it retrospectively, so you don’t have to follow them up for 20 years to find out what happens.