Methods of Sampling

How to get the desired sample size?

Formula:

Where: N is the sample size (population) and e is the desired margin of error.

The margin of error is a statistic expressing the amount of random sampling error in a survey's results. The larger the margin of error, the less faith one should have that the poll's reported results are close to the "true" figures; that is, the figures for the whole population. Margin of error occurs whenever a population is incompletely sampled.


For example:
The sample size of CS students in New Era University is 1000 students. And I want to have 5% of margin error.

Methods of Sampling
A.Random Sampling
-Picking of correspondents, roulette, etc.

B.Systematic Sampling
-Follow the steps:
1.Compute for sample size/total no. of sample
2.List the members of the sample and number them using the quotient of no.1
3.Pick the desired number you want.

For example:
Listed below are 15 CS students, numbered by 4 and I get the 3rd elements to be used on my sample.
1.Wako-Wako
2.Ariane
3.Andrea-----X
4.Shenel
1.Jessy
2.Volts
3.Gene-----X
4.Earl
1.Tomas
2.Lloyd
3.Ranel-----X
4.Jong
1.Jp
2.Jana
3.Lash-----X

Therefore, my respondents will be Andrea, Gene, Ranel and Lash.

C.Stratified
-A method of sampling that involves the division of a population into smaller groups known as strata. In stratified random sampling, the strata are formed based on members' shared attributes or characteristics. A random sample from each stratum is taken in a number proportional to the stratum's size when compared to the population. These subsets of the strata are then pooled to form a random sample.


For example:
I need to gather respondents from 4 sections of CS.

Note: In case there's decimal point for the respondents, just give the decimal point to the other strata. For instance, instead of 71.5 for CS1, trade off the 0.5 to CS4 so that CS4 will have 72 respondents or vice versa. Or instead of CS3 having 85.8 respondents, give 0.8 to CS2 so that it will have 58 respondents or vice versa. If you did not do this, you will encounter problems. The worst, I won't allow a MANANANGAL as my respondent. :)







D.Cluster
-Area sampling

E.Purposive
-Expert sampling

F.Snow-ball
-Referral method

(Source: MAT381 professor and Wikipedia)