Briefly explain the benefits of stratification

Question

this question is based on sampling concepts in survey work

Answer 1

Good Morning,


Some of the advantages of stratification are as follows: 


(1) Reduction of selection bias. Selection bias can result when the selection of subjects into a study or their likelihood of being retained in the study leads to a result that is different from what you would have gotten if you had enrolled the entire target population. You will notice that it is nearly impossible to introduce the entire "population" under study. 

Furthermore, selection bias can result when the selection of subjects into a study or their likelihood of being retained in a cohort study leads to a result that is different from what you would have gotten if you had enrolled the entire target population. 

(2) Stratification - when used accurately - ensures each subgroup within the population is represented in the research study being conducted. 


The most effective way of showing what can occur when stratification is not used, is to demonstrate what takes place when we as researchers use simple random samples, providing you an example. Let's say you as a researcher assign every undergraduate student to one of four sub-populations; male undergraduate, female undergraduate, male graduate and female graduate. Because you want to have your four sub-populations track closely to the population writ large you determine in the process that male undergraduates comprise 45% of the population. In addition, you determine 20% of male graduates comprise the population writ large. However, simple random sampling for your study, you procure 25 male undergraduates and 35 male graduates for your study. Moreover, your sample size (n) equals 100. Without stratification you will end up under-representing male undergraduates and over-representing male graduates which leads your conclusions to error. Because educational achievement has been associated with political views in past research, such errors lead to diminished accuracy of your findings. 


Disadvantages:

(1) Stratified random sampling cannot be done in each study. Several conditions must be met prior to the process being implemented in a study, making it complex to utilize. Consider the following: Researchers must identify every member of a population being studied and classify each of them into one, and only one, subpopulation. Finding an exhaustive and definitive list of an entire population is the first challenge. In some cases, it is downright impossible.

(2) In the example I provided above under advantages, we used something discreet, tangible (i.e graduate, undergraduate, and gender), right? Imagine bringing more complex factors into a study such as race, ethnicity, or even religious proclivity, and you quickly see that stratification can be downright impossible to achieve due to extrinsic factors involved with conducting the study. Simply put, it is not advantageous to you as a researcher to categorize each person into a strata which makes sense, and even if it were, it may be next to impossible to accomplish. 

I hope the above helps you and wish you good luck on your finals as well as a great weekend ahead. Please feel free to ask any question related to my answer in the comment section below.