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(Stratified) Random Sampling

Hey guys,

I just did the following question and now I am confused whether my understanding of stratified sampling is incorrect.

An analyst decides to select 5 stocks for his portfolio by placing the ticker symbols for all the stocks of the NYSE in a large bowl. He randomly selects 5 of these stocks. The analyst used:

A) Dual random sampling

B) simple random sampling

C) stratified random sampling

B) is correct. 

I re-read the learning objective but I am still unsure about the following: arent the stocks of the NYSE already a stratum of all the stocks globally available? If yes, we would have a stratified sample and the solution would bei c)…

What am i missing here?

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it would be stratified if he had placed e.g. all the Small company stocks in 1 bowl, Medium in another and so on..

picked a bowl at random

and then picked 5 out of that bowl.

(Low, Medium High were based on certain parameters)

he had created “strata”

and then picked the sample from those “strata”


I think I got it now. Great, thank you very much, cpk123!smiley​​​