What is Epidemiology?

How likely you are going to change your health-related behavior, if your provider suggests so?

What is your weight status?

How do you prefer to wear your clothes?

Thursday, April 28, 2011

Shall we take turns to drive our vehicles?

There were a quarter billion registered vehicles on highway in 2008. [1] And according to the US Census, there are three quarter of US population own a car and American drives 33.4 miles per day. [2] This is a huge number on vehicle usage and a big difference compare to several decades before. Nowadays, people rely on driving motor vehicles more and more as it is convenient. Not to mention how it changes people’s daily life and contribute to such huge prevalence of obesity rate because of lack of walking for daily exercise. Let’s take a look at other side: how using motor vehicles could impact our environment and affect our health.

Do you know what vehicle exhaust emissions are? In the car exhaust fumes, there are a lot of dangerous chemicals, such as carbon monoxide, nitrogen dioxide, sulphur dioxide etc. Those harmful chemicals could pollute air. And once the polluted air get into human body and transport in the bloodstream to all major organs, it could potentially cause respiratory conditions, such as asthma or bronchitis. [3] Those respiratory diseases are still on the list of top ten leading causes of death, according to the statistical report form CDC. [4] There are also some researches showing that the air pollution caused by driving a car could not only affect human body, but also have regional/global effects. [5] Therefore, this is a huge epidemic problem.

So, how to improve our air quality? There were several regulations established since 1947 regarding to US environmental and occupational health, such as 1947 - Los Angeles Air Pollution Control District, 1959 - California Motor Vehicle Pollution Control Board, 1990 - Clean Air Act Amendments of 1990, etc. [6] Most of those regulations focus on how to improve automobile emission system and set new automobile emissions standards. Besides these, what can we do more to protect our population, especially for our next generation? I think we can propose a new regulation to reduce car usage and eventually reduce air pollution. The regulation would be: people who drive cars with odd number on their plates should only drive on Monday, Wednesday and Friday; People who drive cars with even number on their plates should only drive on Tuesday, Thursday and Saturday; there is no restriction on Sunday.

As an epidemiologist, I think the first thing we could do is establishing a cohort study regarding to test the relationship between car usage and incidence of respiratory disease, such as asthma. [7] For example, we could compare incident rate of asthma between population from small town with little traffic and population from big city with heavy traffic. In order to make it more validate, we should try to balance our sample population in terms of different characteristics, such as socio-economic level, education level, age, gender, ethnicity etc. Then, we could provide evidence-based association to the policy maker to push the policy establishment by ruling out possible confounders.

There are several challenges for conducting such study from epidemiology aspect. Firstly, it is hard to select sample population in order to avoiding selection bias and misclassification. Secondly, it is hard to balance two sample populations in all possible characteristics. Therefore, this study would possible contain some unmeasured confounders. Thirdly, in order to track the incidence of asthma, this should be a cohort study, which is hard to get funded for long research period.

Even though there are several challenges for developing such policy, we still can use this study as a pilot one in order to show the potential benefit to policy makers. And push to establish the policy eventually by providing this evidence-based result. If we could get evidence-based result showing there is a valid association between car usage and asthma, we could suggest policy makers to try this policy in one/two cities and let epidemiologists keep tracking those cities to further evaluate the association. If the incidence of asthma in those cities were reduced, as epidemiologists, we could further push the policy makers to apply the policy to other regions. Once we have this policy, the potential positive epidemiologic outcome would be decreasing incidence of asthma and other respiratory diseases.

There are some challenges from other aspects. For example, some people would think this policy against human right as it restrict when people could drive their cars. This could raise the same reaction as mandate insurance from Health Reform. For example, Missouri passed Proposition C which encourages people to have their freedom to choose insured or uninsured even though it is against mandate insurance. But I think this oppose reaction could reduced after certain time period just like everyone should have a car insurance before driving. People will be used to it. And it is good for our next generation.

Beside the benefit for reducing incidence of respiratory diseases, it could also potentially reduce prevalence of obesity rate. Because when people are restricted to certain days on driving, people would choose other ways for transportation, such as public transportation or bike. Therefore, people would be able to do more exercise than now, if they choose bike or even with public transportation, people need to walk to the station. And from environmental aspect, we could save more energy and protect our earth. By applying this policy, we could also solve traffic jam problem by reducing daily loading, especially in big cities.

Therefore, the benefits for developing this policy would weigh heavier than the challenges. Also, some countries already had similar policy for some big cities with heavy traffic, such as China. If there is no enough funding to conduct a cohort study in US, we could conduct a retrospective cohort study by using data from other countries that already applied this kind of policy and provide evidence-based relevant result to policy makers as epidemiologists. Hopefully, we could push this policy into our real life.
  1. Bureau of Transportation Statistics. http://www.bts.gov/publications/national_transportation_statistics/html/table_01_11.html
  2. http://greenanswers.com/q/53278/transportation/infrastructure/how-many-people-drive-every-day-america
  3. Exhaust emissions: what are they? http://www.bbc.co.uk/health/physical_health/conditions/exhaust_emissions.shtm
  4. Leading Causes of Death. http://www.cdc.gov/nchs/fastats/lcod.htm
  5. Cars, trucks, air pollution and health. http://www.nutramed.com/environment/cars.htm
  6. Timeline of major U.S. environmental and occupational health regulation. http://en.wikipedia.org/wiki/Timeline_of_major_U.S._environmental_and_occupational_health_regulation
  7. Gordis, L. (2009). Epidemiology. Philadelphia, PA: Saunders.

Sunday, April 17, 2011

What are the challenges of a cohort study on following breast cancer survivors for five years?

Cohort study is one type of study design that is normally used to address risk factors/incidence of a certain disease. This type of study usually starts at certain time point with baseline measurement of participants and divides them into different groups, and then follows participants for a long time period to see whether those participants develop a certain disease. In this way, it is easy to address the predictor/factors that would cause/influence this disease/outcome.
As I said in my previous post, my colleagues and I designed a cohort study regarding to test whether people’s clothing preferences would influence people’s weight status. Also, my current research project is to discover predictors for breast cancer-related lymphedema. So, what is lymphedema? Lymphedema is a chronic progressive disease often caused by cancer treatment, especially in patients who require surgical removal of or radiation to lymph nodes.  Breast cancer survivors are at life-time risk of developing lymphedema their cancer treatment likely included surgery or radiation treatment, which may adversely affect the lymphatic system. Therefore, it is a big population based chronic disease.
In this study, we followed breast cancer patients for five years starting from pre-operation as baseline measurement, which means the time period before the patients having breast cancer surgery. We then follow them based on the timeline as shown in Figure 1 [1] and see whether they develop lymphedema afterwards. At every lab visit, we interviewed patients for their symptoms and measured their BMI, etc. The ultimate goal for this study is to discover risk factors of developing lymphedema among all different potential exposures (such as a certain symptom or combination of some symptoms, BMI, etc.) for breast cancer survivors.
Figure 1. Timeline for data collection, where Ti represents the ith visit of a patient. [1]
This study started in 2007, we’ve been following our patients (n=316) for 4 years. The main challenge that I found is follow-up bias. It is really hard to follow people for such a long time period. Even though we did call them several times before their next visit, patients might still not come. Also, even if they did come, they might not obey the timeline that we expect. In addition, patients might exit study or be lost contact. This study is only five year study which is considered as a very short time period for a cohort study, regarding to what Gordis suggested, which is twenty years. [2] Also, there is a funding issue. For this five year study, we got to apply for funding every two/three years. Normally, funding won’t have such a long period. It is hard to continue if it is not funded. And we need to report exciting findings in our annual report in order to keep funding…
Even though I think it is a wonderful and promising research project which could increase awareness of lymphedema, it is hard to get funding and follow participants over time. And there must be unmeasured confounders in our study design, because it is not practical to cover all possible confounders. Additionally, we didn’t have a hypothesis at the beginning which makes the study even harder to measure, because we want to discover as many as possible risk factors of developing lymphedema. Therefore, we could publish a guideline for practitioners of how to manage and control lymphedema. Although, this study has some drawbacks, we could still learn from the findings of this cohort study.
1. Xu S, Shyu CR. Efficient selection of association rules from lymphedema symptoms data using a graph structure. AMIA Annu Symp Proc. 2010 Nov 13; 2010:912-6.
2. Gordis, L. (2009). Epidemiology. Philadelphia, PA: Saunders.

Monday, April 11, 2011

How does preference of clothing style affect your weight status?

Do you know your weight status? What is your clothing preference? Please feel free to answer the poll questions above.

Do you think clothing preferences would affect your weight status? Some of my colleagues and I designed a study on how clothing preference influence weight status. Please click here to read more about our study.