Is a stratified sample considered to be a simple random sample?
No. Stratified sample cannot be taken as simple random sample.
If the size of the universe is less, you shall go for simple random sampling.
Example: Assume you are going to select 5 students form a class of 60. You can write all their names and put them in a box. You select 5 names randomly. No additional process is done in this experiment.
But in case of stratified random sampling, additional processes are followed before arriving at the final selection.
Process 1 - You have to stratify the universe into strata (or groups) according to some trait you can find in the universe.
Process 2 - You have to make the sample a true representative of the universe. For this you have to decide - whether to go for equal representation to all the stratum irrespective of its size or proportional representation by taking into account the size of the stratum.
Process 3 - Finally you select items from each stratum using simple random method.