Probability sampling
means using any sample that has used random selection from the population and
non probability sampling is the contrary process. Sample selection is a very
important part of a survey research study and a unsuitable sample selection can
lead to incorrect inferences about the population under consideration (Groves
at el, 2009).
Probability sampling
assigns an equal or a nonzero chance of selection to all elements of population
(Groves et al, 2009) and this is also the best advantage of this method.
According to Groves et al (2009) the benefit is that we can use one sample
‘realization to estimate the characteristic of the frame population’. Frankfort-Nachmias
& Nachmias (2008) write that probability sample is the ‘only’ method that can
be used representative sample designs. Representative sample designs is an
analysis made using sample units that give results similar to those results
that would have been obtained from the whole population. The distinguishing
factor of probability sample designs that it gives the same probability to each
unit to be included in a sample is also its best advantage.
A well designed sample makes certain
that if the study was conducted repeatedly with different samples then the same
results will be obtained with minimum variation (Frankfort-Nachmias &
Nachmias, 2008). Probability sample designs make it possible for the
researchers to estimate the degree of deviation if the study was repeated. Rao,Hartley & Cochran(1962) reports that the probability method is the simplicity of
calculation and calculating the variance of the estimator.
I would like add an
interesting point to this comparison of probability and non probability
sampling: the probability sampling techniques used in a quantitative research
are ‘rarely appropriate’ when conducting a qualitative research study of the
same nature (Marshall, 1996). I
would also like to add that it is not uncommon for social scientists to use non
probability designs for various reasons: study of an unspecified population or
convenience, cost outweighs other factors.
My final project aims at
understanding if a relation exists between success in life and growing up as an
immigrant or in a cross culture. I prefer to use a proportionate stratified
sample design as in my research the variable of ‘being raised by immigrant
parents/ cross culture’ is already defined. I would use that as the basis of division
as according to Frankfort-Nachmias & Nacmias (2008), when dividing sample
into a homogeneous strata the basis of division is related to the variable. The
sub samples of the sample design would be based upon age of the participants as
well. We are aiming to measure success at various stages in life: high school,
college and then eventually mid life.
References
Frankfort-Nachmias, C., & Nachmias, D. (2008). Research Methods in the Social Sciences (7th ed.). United States of America: Worth Publishers.
Groves, R. M., Fowler, F. J. Jr., Couper, M. P., Lepkowski,
J. M., Singer, E., & Tourangeau, R.
(2009). Survey methodology (2nd ed.). Hoboken, NJ: John Wiley &
Sons.
Marshall, M. N.
(1996). Sampling for qualitative research. Family
practice, 13(6),
522-526
Rao, J. N., Hartley,
H. O., & Cochran, W. G. (1962). On a simple procedure of unequal
probability sampling without replacement. Journal
of the Royal Statistical Society. Series B (Methodological), 482-491.
