Incidence rate in epidemiology can be confusing to say the least. In healthcare and the study of disease, an incidence rate refers to the rate of newly diagnosed cases of a disease or illness. It is generally reported as the number of new cases occurring within a certain period of time.
For example, if over the course of a year, 10 women are diagnosed with breast cancer out of a total sample population of 200, the incidence rate of breast cancer in that population would be 5%. It can also be reported as a fraction of the population at risk of developing a disease (for example, the well-known statistic that one in two people will be diagnosed with cancer in their lifetime, giving an incidence rate of 0.5), and incidence rates can be further broken down according to different subsets of the population such as gender, race, or age group.
Incidence rate, then, not only provides a snapshot of the changes of diseases over time but also allows comparisons to be made on the incidence across different populations - something which can be extremely helpful in healthcare market research. Obviously, the accuracy of incidence data depends on the accuracy of diagnosis and the reporting of the disease, and when it comes to therapy areas that aren’t as well understood or easily diagnosed, many cases go undiagnosed. In these situations, it is usually more appropriate to report the rate of treatment since these are known.
What is prevalence rate?
It’s important not to confuse the incidence rate with prevalence, which refers to the actual number of live cases of a disease or illness and includes recently diagnosed cases with live cases. So, for instance, if out of a population of 50,000 people, 1,000 were recently diagnosed with cancer and 4,500 are already living with it, the prevalence would be 0.11 (or 11,000 per 100,000 people).
And what about incidence rate in market research?
This is where things get even more confusing! The ESOMAR glossary defines incidence rate in market research as “the proportion of respondents contacts in a survey who qualify for the survey”. That means that in quantitative research, incidence rate is defined as the number of respondents from a sample that will qualify for your study. So, if your market research survey is looking to target females only from a random sample, your incidence rate would immediately drop from 100% to ~50%, and if you are looking to target females with children under the age of 18, your incidence rate would drop even further. Add medical market research and the question of incidence rates in diseases into the mix, and things become more complicated still. For the sake of this blog, we are going to focus on incidence rate in terms of disease and illness - but actually, however you look at incidence, the results are the same: low incidence generally means more complex research.
Breast cancer incidence rates
Let’s look at the incidence rate of breast cancer for an example:
- There are around 55,200 new breast cancer cases in the UK every year
- It’s the most common cancer in the UK, accounting for 15% of all new cancer cases
- Incidence rates for breast cancer in the UK are highest in people aged 90+
- There’s an incidence rate of 60 per 100,000 in women aged 35-39
- Since the early 1990s, breast cancer incidence rates have increased by 20%
- This is expected to rise by 2% between 2014 and 2035
- Breast cancer is more common in White females than in Asian or Black females
So what does this mean for healthcare market research?
When it comes to healthcare market research, incidence rate can have a significant impact on the ease with which researchers can access respondents and encourage them to take part in the research. Conditions with a low incidence rate are significantly harder to recruit for, which can impact the overall feasibility of the study and make it much more expensive and time-consuming. Not only is there a smaller pool of potential respondents, but these respondents will most likely be spread out across different locations and will be harder to tempt to take part. So as well as taking more time and effort to recruit, incidence rate can also affect things such as criteria, incentives, and methodologies:
Be realistic about your criteria
Incidence rate can have a big impact on how specific you can be with your research criteria. Basically, the more specific the audience, the lower the incidence rate. For example, if we look at our breast cancer incidence above, consider if you were looking to recruit breast cancer patients aged 30-60 who have been diagnosed in the last two years and take a specific medication. Alternatively, you could be looking to recruit Asian breast cancer patients who have been diagnosed in the last two years, are aged 30-39, and have been taking a specific medication for at least one year.
The second example would be much more complicated, so you need to separate the must-haves from the nice-to-haves to ensure your research is still feasible. If you need to conduct research with Asian females, for example, perhaps you could be more flexible with age, when they were diagnosed or how long they have been taking the medication for? Alternatively, if age is focal to your study, could you be more flexible with race or expand your criteria to those who have been diagnosed in the last five years and have taken your chosen medication for a non-specific time period? By being flexible with your criteria where possible, your low incidence research will become much more achievable.
Allow enough time for recruitment
It might seem obvious, but the lower the incidence of your therapy area, the longer it will take to recruit. First of all, your patients will be harder to find, and depending on how to plan on reaching them, you have to ensure you allow enough time to do so. If you are using HCPs or support groups to access participants, for example, a support group for young women with breast cancer, you have to allow enough time for them to reach out to patients - and also remember that support groups or charities might have their own restrictions in place which can hold things up further. These support groups might also only meet up once a month, which means you need to factor the frequency of support group meetings into your research timescales too.
If you decide to use KOLs to reach out to participants - which can be very helpful in the study of low incidence diseases -the same goes. Perhaps they only run specialist clinics once every few weeks? If so, you need to allow for this when deciding on your recruitment timeline. And that’s not the only thing to consider: above all, you have to make sure your participants are will to take part, too. When dealing with low-incidence rate diseases, especially around sensitive subject matters such as breast cancer, you have to give your participants enough time to decide they want to take part. Low-incidence diseases are often quite emotional and private, so you can’t rush this decision. With all this in mind, we usually recommend that our clients allow four to six weeks for recruitment.
Carefully consider your incentive
Generally speaking, the lower the incidence rate, the higher the incentive, but it’s also important to consider fair market value. It’s standard market research best practice to offer an incentive to participants to thank them for giving up their time to take part in market research, and the incentive amount you decide on will depend on a lot of different things, from the complexity of the study to the duration and even the type of methodology. Your incentive will also need to reflect the therapy area being researched, too. Low incidence rate diseases are often a rare and sensitive subject matter, which means you’ll need to offer a higher incentive.
Your incentive also needs to reflect how difficult the recruitment is, too. For example, your incentive for a study on allergy is going to be completely different from our breast cancer study example above. You’ll need to make sure you choose the right type of incentive, too. Often, for those living with rare or life-limiting conditions, the chance to have their voice heard and tell their story is enough to tempt them to take part, although other ideas include a charitable donation, cash, cheques or even shopping vouchers.
Need more advice on incidence rate?
Incidence rate in healthcare can have a knock-on effect on healthcare market research, impacting everything from timelines and cost to criteria and even incentive. If you’ve been asked to conduct research in a rare or low incidence therapy area and are looking for advice on incidence rate in market research, with more than 25 years’ experience, at GKA, our expert team will be more than happy to help.
In the meantime, why not check out some of our blogs about hard-to-reach respondents for more hints and tips?