# Statistics in our daily life

Last updated: Sep 2024 | Estimated read time: 10 min

## TLDR

The aim of this article is to put on scene different ways to use the statistics "philosophy" or method in our life, as well as make clearer the way statistics works. Because stats might seem reserved only for some people, I want to give you the taste of how it feels to think like a statistician and give you reasons to do the same. You will see that you don't need any math or pre-requisite for this and that it might be more relevant than you think.

## Estimation

It is very common in statistics to want to "estimate" things. These can be the average body mass index of undergraduates, as well as more complex examples such as the vector of coefficients that best fits a regression between several variables. An important part of what an estimator is is the fact that we will never know its "true" value. The more information we have (quantity and quality), the more accurate our estimate will be, but it will never be sufficient.

Let's say we are interested in the average number of hours a student works before an exam. One way to estimate this is to ask different students during the course and calculate the average. Since it is impossible to survey every student in the world, how do we know if the value we will get is relevant to our goal? We consider an estimator to be good when it respects certain properties.

### Is our estimaton biased?

A bias is simply a deviation from the original objective. Whether in statistics or in "real life", it has the same meaning. One can think of cognitive biases, statistical biases or more generally scientific biases. An estimator can be considered as unbiased if the difference between the expected value of the parameter studied (i.e. what we are supposed to obtain if we can interview an infinite number of students) and the "real" (or "true") parameter is zero. But one could say that if we already knew the "true" value of the parameter, why bother making an estimate? In fact, we don't know it and that's the problem: it is not so easy to know if our estimator is biased or not.

Fortunately, we have mathematical statistics that can determine whether an estimator is biased or not, but they are not sufficient because they regularly assume assumptions that are not always verified (we won't talk about this in more detail here because it is mostly about mathematics and the way we collect our data).

If we return to our example with the average number of hours students work before an exam, it's easy to find biases. For example, asking only students during class implies that students who do not attend class will not answer our question. And it seems plausible that students who don't go to class work less (or more? who knows) for exams. And if we take a completely opposite example like "How many beers did I drink last year per week on average?", I have to think about things like "Does my current consumption influence what I think I drank last year?". At this point, you might start to wonder why being so methodical about such unimportant questions. You'll find an answer to that question at the end of this article and you might be surprised.

### Does our estimaton have high variance?

The variance is simply a measure of dispersion. It tells us how far people in our sample tend to deviate from the mean. In contrast, a variance of zero is equivalent to everyone having the same value (i.e. in our example, all students work the same amount of time before an exam). The connection to estimation is the fact that we want to know if our estimator has a high or low variance.

This is important because a low variance implies that, especially if our estimator is unbiased, we can be sure that we can make generalizations from our sample to the rest of the world. For example, if we estimate that a student works an average of 4 hours before an exam and we know that this estimate is unbiased and has a low variance, it is very likely that the "true" value is around 4.

It is important to keep in mind that we make estimates all the time. When you wonder if you're going to find a place to park your car, which college is best for you, or if you've eaten too much, you're making an estimate. You're trying to figure something out, but because you don't have all the information in the world, you're making an approximation based on what you know.

To that end, I think the best way to make a better estimate is to think about the possible biases and the level of variance in your estimate. In this way, it will naturally force you to doubt your beliefs and describe the problem at hand more formally.

## Inferences

The purpose of estimation is to make inferences. As we said before, you don't have all the information in the world. If this were not the case, estimation would be meaningless. You only have access to a (very small) sample of information, and we can define some criteria that tell us whether, based on our data, we can make generalizations to the rest of the world from that sample. In statistics, a very common way to do this is to calculate the p-value.

For example, if we want to know if a drug is effective in reducing LDL blood cholesterol, we give it to people with high LDL and after a week compare the difference with people who also have high LDL but did not take the drug (preferably a placebo). From there, assuming the drug is not effective, we can calculate what the probability is of getting the results we did (e.g., people who took the drug reduced their LDL by 10 points and those who took the placebo by only 4 points). If this probability is very low, we can deduce that our initial hypothesis might not be true (i.e. that the drug is effective for reducing LDL blood cholesterol!).

The convention is 5%. If a difference of 6 (10 - 4 = 6) had a probability of less than 5% of occurring, we say that our result is significant and that we cannot accept the hypothesis that the drug is ineffective.

This concept of p-value implies other important concepts. If we take the convention of 5%, this amounts to taking a 5% risk threshold to conclude that there is an effect even if this is not the case in practice. In a slightly more formal way, we can describe:

False positive: conclude that there is an effect even if there is not.

False negative: conclude that there is no effect even if there is one.

You can familiarize yourself with these concepts by thinking about a COVID-19 test. There is a probability that it will say you have it even if you don't, as well as a probability that it will say you don't have it even if you do (a bit more problematic). In practice, there is a trade-off between maximizing and minimizing the probability of false positives or negatives. In the clinical field, one would naturally prefer to minimize the probability of telling a person that there is nothing wrong with them when they are sick. This statistical concept is very important in the medical sciences.

### More details

There is a lot of criticism of the P-value and many people (even those who regularly do statistics) don't really understand what it means. In fact, the people who criticize the P-value are mostly criticizing the way people tend to use and interpret it. For us, it doesn't really matter because I just want to give you the conceptual idea of what a p-value is: a way to define whether what we observe is sufficiently unlikely and we have to say "something is happening" (in the latter case: the drug is not ineffective).

## Bayesianism

Bayesianism is an approach that assumes that beliefs can be formulated as probabilities (of distribution). For each subject in life, we can subjectively associate a probability distribution of what is true, and update this distribution with new information. Let's take an example: I believe that it rains almost every Sunday in Bordeaux. I have this belief because since I moved to Bordeaux, it rains almost every Sunday. But last year, for some reason, every other Sunday was very sunny. Adding this information to my last belief (and if I am a rational Bayesian person), I would have to change my belief. My new belief about Sunday weather in Bordeaux is more nuanced than my old belief. If I believed that 95% of Sundays are rainy and last year I only observed 50%, I need to update my belief and it will be about 70% (or any other value between 50 and 95, depending on other parameters).

Bayesian statistics work the same way. This drug has been shown in the past to reduce blood sugar by 3 units, but in the last 3 published RCTs (clinical trials), the average effect was 2. We should start thinking that the average effect of this drug might be about 2.6 (for example). And you can use this approach for literally anything related to knowledge (i.e. a lot of things). Non-exhaustive list of questions for which it is relevant to think like a Bayesian:

- This professor was absent one out of three times last year, but only one out of ten times last semester.
- Every time I run, my leg hurts. But since my surgery, it only happens when I have a bad night.
- I think vegetarianism is bad for your health, but a study published in Nature tends to show that vegetarians have no deficiencies and are not less healthy.

Whenever you have new information, add it to what you already know in order to update your beliefs and always improve.

You may think this is a way of thinking that you already do sometimes, and it's probably true: it's pretty intuitive to change what we believe based on new information. But I suggest that you use this approach most of the time. Mainly, it will force you to be open-minded: unless you consider that you already know everything, new information is always better. You just have to give low "weight" to information that you consider poor. In fact, information from a top-notch peer-reviewed scientific paper is much better than a random Facebook user's comment on the same topic: you can't give it the same credit. You will have the opportunity to change what you think all your life and never have a closed opinion, but also to constantly remind yourself that there is a lot you don't know.

For all these reasons, I strongly encourage you to think this way.

## Machine learning

Machine learning is a very popular field whose goal is to use optimization algorithms to create mathematical models capable of "predicting" things. Recommendation systems, chatGPT or tumor recognition from MRI scans are entirely based on advanced machine learning algorithms. I don't think they can be considered as pure statistical tools, because it is quite difficult to interpret what they "learn" from the world: they are excellent at predicting, but not so much at explaining. But as I probably said, the purpose of statistics is to give us information that we cannot perceive with raw data. However, there are still many useful concepts for what we are talking about here.

Let's say I want to create a model that can predict if a person has a tumor using an MRI scan. To do this, I've created a dumb model that can't do anything right. When I show it a scan and ask it if there is a tumor, its answers are purely random. Then I show it a lot of MRI scans with and without tumors and tell him for each one if there is one or not. By doing this (and using optimization algorithms), it starts to learn the difference between good and bad MRI scans. Now my model is much better than it was at the beginning and I ask if there is a tumor on the new scans that it hasn't already seen. If I did all the last things right, my model can now predict if a person has a tumor using MRIs. It has "learned" from the example and is now able to generalize to new scans.

If you understood that last point, you now have in mind the main idea of how machine learning works. Of course, it is much more complex in practice, but we use exactly the same logic when we train a model to perform a task.

### Over/under-fitting

Overfitting and under-fitting are two very important concepts in machine learning. Over-fitting occurs when we train our model, it learns so much from the example you gave it that it cannot generalize to new examples. This can happen when we over-train a model, for example. An analogy would be a student who memorizes all their lectures, but doesn't know how to respond when the professor asks a question that is based on understanding the lecture, not memorizing it (sound familiar? Yeah, me too).

Another way to think about this concept is to consider that our experience is representative of what happens to others in life. Over the course of our lives, we have many experiences, learn from them, and then try to avoid the mistakes and repeat the positive things. This is fine until the overfitting occurs: we should not be overconfident in generalizing to new events since our experience is not necessarily representative. Also, you can see here that more experience could lead to more overfitting. One way to overcome this is to "train" yourself with a "variety of data": get into the habit of asking other people what they think about things you have experienced and compare the differences.

On the other hand, under-fitting is when a student has not studied enough for an exam and simply cannot answer the questions. For example, it's like having no experience in public speaking and trying to give advice to others. You don't need to know everything, and being "sub-competent" in a given area is not a problem at all. It's actually an excellent quality to know when we don't know (probably more often than we'd like).

## Closing remarks

This might be a good time to explain why being so methodical, even for unimportant matters, is so important. The main reason is that it creates excellent habits of epistemology. You will be more open-minded, better at describing problems formally, more critical of yourself, and learn from others. I really believe that most of our beliefs come from the way we approach information based on our epistemological habits, i.e. on a day-to-day basis.

Another benefit of using all of these concepts on a daily basis is the fact that it makes the discussion much more precise, fun, interesting and with a great vocabulary. You can't imagine how nice it is to have a discussion with someone who always uses the right term and how easy it is to understand the point.

This article was just an introduction to many different concepts that would all deserve a full book. I made a lot of approximations because my main goal is not to be accurate but to give you the intuition of how statistical methods work. If you don't come from a stats background, I hope you have a better understanding of stats and have found some useful concepts here for you. If you do statistics regularly, I hope you'll start thinking about using these concepts outside of work. If you are somewhere in between, I hope you learned something.

## Feedback

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