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For more information, go to www.arthritisresearchuk.org

Frequently asked questions

1. What is the Musculoskeletal Calculator?
2. Why have we developed the Musculoskeletal Calculator?
3. Why are they estimates?
4. How did we collect the data?
5. How accurate are the estimates?
6. How did we analyse the data?
7. How did we identify data on the risk factors?
8. How can you know how many people have these conditions if many are undiagnosed?
9. What's the difference between (Total) and (Severe) osteoarthritis?
10. I've chosen more than one area to compare, and the percentage prevalence is the same for all areas in all the risk factor categories, why is that?
11. Where can I learn more about what you are doing for people with a musculoskeletal condition?
12. Why can't some of the categories be selected for hip and knee osteoarthritis (severe)?
13. How can I find out more?

1. What is the Musculoskeletal Calculator?

The Musculoskeletal Calculator is a tool designed to produce prevalence estimates (i.e. how many people have a particular condition) for musculoskeletal (MSK) conditions.At this stage, estimates for osteoarthritis, and severe osteoarthritis, of the hip and knee are produced. These can be analysed in a number of different ways, including by local authority area.

2. Why have we developed the Musculoskeletal Calculator?

The conditions included in the Musculoskeletal Calculator were chosen because local estimates on their prevalence are not currently available for the UK in general and England in particular. And, because what gets measured often gets done, musculoskeletal conditions can often be overlooked. Because power over so much of the healthcare system, and in particular public health, rests at a local level, it is vital that choices are made that take into account the prevalence of musculoskeletal conditions.

3. Why are they estimates?

The data provided is an estimate because it is not presently possible to access the data required to say how many people have a musculoskeletal condition. Most of the treatment for musculoskeletal conditions occurs in primary care and this data is not currently collected by the NHS. Arthritis Research UK is campaigning for more data on musculoskeletal conditions to be made available.

4. How did we collect the data?

The English Longitudinal Study of Ageing (ELSA)  - a large multicentre and multidisciplinary study of people aged 50 and over and their younger partners, living in private households in England – was chosen as the basis for the prevalence models the calculator produces. This particular survey was chosen because the sample used in ELSA was designed to be nationally representative and since osteoarthritis is rare under 50 years of age.

5. How accurate are the estimates?

The numbers and percentages from the Musculoskeletal Calculator are estimates based on statistical models. However, the survey we used to produce these models and estimates (ELSA) is a national survey which is designed to give a representative picture for England as a whole. National bodies routinely use survey data: for example, ELSA is jointly funded by UK government departments and the National Institute on Aging (USA) , and “helps the government plan health care services and pensions systems to accurately meet the needs of older people”.

6. How did we analyse the data?

We commissioned the osteoarthritis estimates in the model from Imperial College London.

After analysis, survey information contained in ELSA was combined with known local data about the different risk factors, including:

  • smoking status
  • obesity rates
  • age
  • gender.

7. How did we identify data on the risk factors?

We reviewed scientific literature to identify risk factors which increase/decrease the chances of developing osteoarthritis of the hip or knee. For example, there’s a clear link between obesity and osteoarthritis of the knee.

Answers to questions in the ELSA survey relating to these risk factors were then analysed. For example, questions relating to weight were fed into the analysis of the risks caused by obesity.

From this, the following risk factor variables have been included in our models:

  • age
  • gender
  • ethnicity
  • socioeconomic status
  • education
  • body mass index (BMI)
  • physical activity
  • smoking status
  • gym/sports club membership.

As with all surveys, some data was missing. There are specific statistical techniques that take into account missing data.

8. How can you know how many people have these conditions if many are undiagnosed?

Because there's no simple test for osteoarthritis, diagnoses vary greatly between individual GPs and across general practices. GPs often using symptom labels such as 'knee pain' rather than a diagnostic label of osteoarthritis1.

Because of this, out of an estimated 8.75 million people in the UK1 who have sought treatment for osteoarthritis, many remain undiagnosed.

Two main groups were included in the Musculoskeletal Calculator as having osteoarthritis of the hip or knee:

  1. Survey respondents who reported that they have doctor-diagnosed osteoarthritis.
  2. Respondents who reported consistent hip or knee pain.

9. What's the difference between (Total) and (Severe) osteoarthritis?

Total osteoarthritis includes all cases of osteoarthritis of the hip or knee.

Severe osteoarthritis includes cases that would require special attention, and additional resources, from healthcare providers and commissioners.

This definition was developed using two survey questions:

  1. ‘Severity of pain most of the time’
  2. ‘Difficulty walking ¼ mile unaided’.

Respondents were deemed to have ‘severe’ osteoarthritis if their answers included any one of the following statements:

  • They have severe pain most of the time (as opposed to ‘mild’ or ‘moderate’).
  • They're unable to walk ¼ mile unaided (as opposed to ‘no’, ‘some’ or ‘much difficulty’).
  • They've previously undergone hip or knee replacement due to arthritis.

10. I've chosen more than one area to compare, and the percentage prevalence is the same for all areas in all the risk factor categories, why is that?

The Musculoskeletal Calculator is a series of statistical models, developed by Imperial College London. For each risk factor category, the model is expressed in percentage terms. This percentage is then applied to an area’s population to produce the result: how many people in a specific area have a certain condition. For very defined sets of risk factors, these will be the same. So, for example, if you choose the following combination of risk factors: Male, Aged 45 - 64, Sedentary (< 30 minutes activity), Underweight, Educated, Never Smoked, Higher managerial, the result will always be 7.44%. The equivalent number of people will then change based on each area’s population profile. To see the difference in figures please choose population counts instead of percentage prevalence.

11. Where can I learn more about what you are doing for people with a musculoskeletal condition?

Arthritis Research UK is constantly seeking to make sure that the needs of people with musculoskeletal conditions are considered when decisions are made about the healthcare system.

You can learn more about what we’re asking politicians to do by reading our manifesto.

12. Why can't some of the categories be selected for hip and knee osteoarthritis (severe)

Due to the data we have available not all conditions cover every risk factor e.g. 'socioeconomic status' and 'level of education' are not part of the model for hip osteoarthritis (severe). When choosing multiple conditions, only risk factors that these conditions have in-common will be available.

13. How can I find out more?

If you wish to find out more about how the prevalence totals were modelled by the Imperial College London team, you can download the technical document (Doc 908 KB).




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