Medicine is a science of uncertainty and art of probability.
The ashes cricket test match was at a very interesting juncture on the fifth day. “There is 30% chance of rain today,” was the weather forecast for the day. A friend of mine was a bit depressed after hearing this. “Why are you depressed?” I asked him.
“Well, there is a 30% chance of rain,” he said.
“Can you tell me about your understanding of 30% chance of rain?” I asked.
He scratched his head for a while and said, “It’ll rain in 30% of the area.”
“But they have said 30% chance, not area.”
“Hmm… let me think… yes.. it probably means it will rain 30% of the time.”
“Again you are conflating time with chance… are you sure about what it truly means?”
“May be 30% of the weather experts think that it will rain today.”
“No. All the experts are saying that there is 30% chance of rain today.”
Now, he was exasperated and desperate to know what the correct answer was.
“It will rain somewhere in the area on 30% of the days in which such prediction is made… is probably the answer that is closest to the truth,” I said.
Probability is the most ill-understood concept even by graduates of science. As a doctor, it makes it very cumbersome to explain to the patient the probability, and hence the risks and benefits, of the surgery or any procedure. The patient signs on the dotted line of the consent form after listening to you, however you are not sure if he has properly understood the essence of the conversation on the risks involved and the probabilities of adverse outcomes.
Here is a conversation with a patient who is a well-known businessman in the area.
“You need an angioplasty and a stent to a couple of arteries supplying the heart. The procedure is a bit more complex than average.”
“OK doctor. I hope there is a guarantee of success.”
“No. There are no guarantees in life in general and medicine in particular. I can’t guarantee even my own return to home from work today. Who am I to give guarantee on your life, that too after a complicated procedure?”
“Is the procedure risky?”
“The risk of a major complication like stroke, heart attack, renal failure, fatal bleeding is about 4% and risk of death is about 1%.”
“That’s scary! Why are we then even considering this operation?”
“Because if we don’t do it the risk of a heart attack or death in the next one year is close to 15 percent.”
“So, I will have to take a 5 percent risk of having a major complication including death in one day to offset a 15 percent risk of death in the next one year, right?”
“Correct.“
“Is that risk worth taking?”
“That’s mostly your call. I can help you in taking the decision by answering your questions and queries.”
“OK. So, which are the four complications that you are talking about?”
“I am not talking about 4 complications but about 4 percent risk of complications.“
“So does it mean I can get 4 out of 100 possible complications that can occur?”
“No. It means if I operate on 100 patients like you, 4 will get major complications and 1 will die.”
“I don’t want to know about those five patients. Tell me about me.”
“I don’t know about you. You will just be one of those hundred patients.“
“If you can’t tell about what’ll happen to me, what’s the point in having all this discussion?“
“The point of having this discussion is to help you make an informed decision. It will help you understand the risk of you coming out of the cath lab with a major complication that includes death.”
“And what is that risk?’’
“It’s about five percent.’’
“But if I get it, it’s 100 percent for me.”
“It’s an incorrect way of saying it. Risk is always calculated before the event. Everything is 100% after the event… good or bad.”