Question

Question one: Pick one of the following sampling methods (simple random sampling, systematic, cluster clamping, stratified sampling). Describe how you would implement this sampling method if you were going to create a sample of 50 students.

Question two: What in your judgement is wrong with convenience sampling? Also, describe a situation where in your judgement conveniences sampling might be appropriate and explain why.

(Response 100 words if possible)

Answer 1

Question 1) :

Simple Random Sampling:-

Simple random sampling (SRS) is a method of selection of a sample comprising of n number of
sampling units out of the population having N number of sampling units such that every sampling
unit has an equal chance of being chosen.
The samples can be drawn in two possible ways.
 The sampling units are chosen without replacement in the sense that the units once chosen
are not placed back in the population .
 The sampling units are chosen with replacement in the sense that the chosen units are
placed back in the population.
1. Simple random sampling without replacement (SRSWOR):
SRSWOR is a method of selection of n units out of the N units one by one such that at any stage of
selection, anyone of the remaining units have same chance of being selected, i.e. 1/ . N
2. Simple random sampling with replacement (SRSWR):
SRSWR is a method of selection of n units out of the N units one by one such that at each stage of
selection each unit has equal chance of being selected, i.e., 1/ . N .
Procedure of selection of a random sample:
The procedure of selection of a random sample follows the following steps:
1. Identify the N units in the population with the numbers 1 to N.
2. Choose any random number arbitrarily in the random number table and start reading
numbers.
3. Choose the sampling unit whose serial number corresponds to the random number drawn
from the table of random numbers.
4. In case of SRSWR, all the random numbers are accepted ever if repeated more than once.
In case of SRSWOR, if any random number is repeated, then it is ignored and more
numbers are drawn.Such process can be implemented through programming and using the discrete uniform distribution.
Any number between 1 and N can be generated from this distribution and corresponding unit can be
selected into the sample by associating an index with each sampling unit. Many statistical softwares
like R, SAS, etc. have inbuilt functions for drawing a sample using SRSWOR or SRSWR.

Question 2) :

The most obvious criticism about convenience sampling is sampling bias and that the sample is not representative of the entire population. This may be the biggest disadvantage when using a convenience sample because it leads to more problems and criticisms. Systematic bias stems from sampling bias. This refers to a constant difference between the results from the sample and the theoretical results from the entire population. It is not rare that the results from a study that uses a convenience sample differ significantly with the results from the entire population. A consequence of having systematic bias is obtaining skewed results.

Another significant criticism about using a convenience sample is the limitation in generalization and inference making about the entire population. Since the sample is not representative of the population, the results of the study cannot speak for the entire population. This results to a low external validity of the study.