How many are there? - Which method is better?

Hi Anonymous,

you should always use the second method (b). The first method (a) is not as accurate for two reasons:

• it neglects the frequency people have using a vehicle, as Vlad mentioned
• it assumes that a single transportation vehicle can be used only once in a specific period of time

If you find how many people in the US use commercial planes, for example, you are not considering that they may use a commercial plane more than once in your selected period of time. Also, you are not considering that the airplanes can be used more than once.

Let's see that with an example.

Let's say that in a generic country you have 100M people taking a flight every year. For simplicity, let's say airplanes just go from point A to point B and the other way round. Let's say that there are 200 people per airplane as possible occupancy and that you have a 75% occupancy, thus 150 people per airplane on average.

Application of method a

Applying 100M/150, you find 670k airplanes approximately

Application of method b

For this method, you need to know

• Frequency of usage - let's assume 4 flights per year per person in this particular country
• How many times the airplane can be used again by someone else - let's say the airplane goes from A to B to A in 24h

Let's assume for simplicity 50% of the trips are from A to B and 50% from B to A.

The yearly number of trips is equal to 100M*4=400M, let's assume equally distributed during the year

This means that daily you have 400M/365 = 1.1M trips, of which 550k from A to B.

Thus, the number of airplanes needed in this country is 550k/150= 3.7k

As you can see, using the correct approach b, which takes into account frequency and multiple usage of the vehicles, you get a completely different number compared to approach a.

Hope this helps,

Francesco

(edited)