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Peter
Answering Biostatistics Questions For IFOM And The USMLE: Part 1
~2.9 mins read
Answering Biostatistics questions for IFOM and the USMLE: Part 1
Let us look at the sample NBME question below:
A community public health department has a limited budget for new interventions and must decide between two options. Option A is to reduce exposure to an industrial chemical that increases the risk for leukemia from 0.5 per 100,000/year to 2.0 per 100,000/year. It is estimated that 30% of the working population in the community is exposed to this agent. Option B is to reduce exposure to a different toxin that increases the risk for aplastic anemia from 0.5 per 100,000/year to 50 per 100,000/year. It ¡s estimated that 5% of the working population is exposed to this toxin. The estimated cost of each intervention is US $740,000. It is assumed that each intervention program will have similar effectiveness in eradicating the exposure. The case fatality rates are similar for both diseases. Which of the following is the best rationale for the health department to use in selecting an option?
A) Option A because more fatalities will be prevented
B) Option A because more workers are exposed to the toxic agent
C) Option B because more fatalities will be prevented
D) Option B because more workers are exposed to the toxic agent
E) The best approach cannot be determined based on the information provided
Dissecting the question
- This question targets the topic: Relative Risk [Relative risk is a high yield topic]
- The quick formula for Relative Risk for this purpose is to divide:
Exposed group (or no treatment) / Unexposed group (or with treatment)
- What these kinds of questions ask, is for you to compare the risk of Option A relative to Option B.
- Every other information in the vignette isn’t needed to arrive at the answer.
- You can easily spot this type of question by looking for the keyword “Risk” when you are asked to compare one group to another (Just like the above question).
Solving for an answer:
From Option A (Risk for leukemia):
Exposed group = 2
Unexposed group = 0.5
Putting in the formula:
2/0.5 = 4% (Relative Risk of 4)
From Option B (Risk for aplastic anemia):
Exposed group = 50
Unexposed group = 0.5
Putting in the formula:
50/0.5 = 100% (Relative risk of 100)
So the Risk in Option B is 100% relative to that in Option A which is 4%.
It means it would be better to invest in an intervention that would reduce the risk of disease by 100% than to invest in one that reduces the risk by only 4%.
The answer is "Option C) Option B because more fatalities would be prevented".
It is not “D) Option B because more workers are exposed to the toxic agent” because we are working with the risk increased per year in each option (i.e 100,000/yr), we are not working with the percentages of workers exposed to the agents. The reason is, even though 30% of workers are exposed to Option A’s agent the risk of getting leukemia is 4%. For Option B, only 5% of the working population is exposed to it, but the risk of getting aplastic anemia is 100% from the calculation.
Take home:
When you meet any biostat question that wants you to compare risk in one group to another,
- Remember relative risk
- Extract exposed numbers and unexposed numbers from the questions
- Divide E (exposed) with U (unexposed) [E/U = RR]
- The group with the highest number has the more risk and vice versa.
- Every other information from the vignette may not be helpful
- All the methods or assumptions in these questions might not be perfect but if you grasp the concept, you'll find it easy to answer similar questions.
Reference:
1. Topic: Relative Risk. Book: First Aid for the USMLE step 1 2019. Public Health Sciences/Biostatistics section.
Reference:
1. Topic: Relative Risk. Book: First Aid for the USMLE step 1 2019. Public Health Sciences/Biostatistics section.
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Peter
Banana Leaves Have Always Been Used In Africa, It Is Now Replacing Plastics In Thailand Plus
~1.3 mins read
A Thailand supermarket came up with a genius way to reduce plastic packaging: wrap its produce in banana leaves instead.
The banana leaf packaging comes from the Rimping supermarket in Chiangmai, Thailand. A real estate company in Chiang Mai, Perfect Homes, posted photos of the banana leaf packaging to their Facebook page and it quickly gained widespread attention.
Of the 9 billion tonnes of plastic ever produced, only 9% has been recycled. This, along with projections of rapidly increased plastic manufacturing, has led to global attention to single-use plastics.
The United Nations Environment Programme estimates that by 2050 there will be 12 billion tonnes of plastic in landfills, the environment, and oceans. Of this waste, cigarette butts, plastic drinking bottles, food wrappers, and plastic grocery bags are the biggest contributors.
The use of banana leaves instead of plastic for packaging vegetables is a great way to reduce single-use plastic. While it looks like they use some plastic for adhering the label, this method significantly reduces the amount of plastic required. They are simply wrapped in a banana leaf and secured using a flexible piece of bamboo. Banana leaves are a great alternative to plastic as the leaf is large, thick and supple enough to be folded.
One thing to consider is the relative cost of plastic versus banana leaves. In tropical locations, banana leaves are readily available locally and could be acquired for free depending on the quantity needed. In more temperate locations the use of banana leaves could be significantly more expensive than plastic. However, using local biodegradable products could be a good alternative in locations where bananas don't grow.
The use of banana leaves to wrap food in has a long history. In some tropical regions of Mexico, tamales are wrapped in banana leaves. Hawaiians use banana leaves during pig roasts to protect the pig from the hot lava rocks. They are also used to wrap sticky rice in southeast Asia.
The banana leaf packaging comes from the Rimping supermarket in Chiangmai, Thailand. A real estate company in Chiang Mai, Perfect Homes, posted photos of the banana leaf packaging to their Facebook page and it quickly gained widespread attention.
Of the 9 billion tonnes of plastic ever produced, only 9% has been recycled. This, along with projections of rapidly increased plastic manufacturing, has led to global attention to single-use plastics.
The United Nations Environment Programme estimates that by 2050 there will be 12 billion tonnes of plastic in landfills, the environment, and oceans. Of this waste, cigarette butts, plastic drinking bottles, food wrappers, and plastic grocery bags are the biggest contributors.
The use of banana leaves instead of plastic for packaging vegetables is a great way to reduce single-use plastic. While it looks like they use some plastic for adhering the label, this method significantly reduces the amount of plastic required. They are simply wrapped in a banana leaf and secured using a flexible piece of bamboo. Banana leaves are a great alternative to plastic as the leaf is large, thick and supple enough to be folded.
One thing to consider is the relative cost of plastic versus banana leaves. In tropical locations, banana leaves are readily available locally and could be acquired for free depending on the quantity needed. In more temperate locations the use of banana leaves could be significantly more expensive than plastic. However, using local biodegradable products could be a good alternative in locations where bananas don't grow.
The use of banana leaves to wrap food in has a long history. In some tropical regions of Mexico, tamales are wrapped in banana leaves. Hawaiians use banana leaves during pig roasts to protect the pig from the hot lava rocks. They are also used to wrap sticky rice in southeast Asia.
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