Lec 2 Sampling Flashcards
Sampling
The process of drawing a number of
observations (or measurements ) from a population
sample
is “a smaller (but hopefully representative)
collection of units from a population used to determine truths
about that population”
What the factors that influence
sample representativeness
Three factors
.Sampling procedure
•Sample size
•Participation (response)
The sample must provide…………..of ……………from which it drawn representative
An accurate picture
Population
The sample is…………..of ………
Subset of population
REASONS FOR SAMPLING
Why Sample?
Time 🕰️
Cost 💲
Improve data quality
Possibility
Accuracy
Time 🕰️
Cost 💲
Improve data quality
Possibility
Accuracy
Time :
Samples can be studied more quickly than population
Cost
A study of a sample is less expensive than that of an entire population
Improve data quality
Obtain in-depth information about each subject rather than superficial
data on all
A study of a population is impossible in most situations
Accuracy
Samples are more often accurate than results based on a population
Types of sampling
- Probability sampling
techniques. - Nonprobability
sampling techniques.
In a probability sampling technique, each
participant in a study population has
an equal
(or at least a known) chance of being selected.
probability sampling technique,
The method protects the research from bias
and ensures that the sample is a true
representative of a population
In a nonprobability technique, each
participant does not have an equal chance of
being selected.
T/F
True
In a nonprobability technique, each
participant does not have an equal chance of
being selected.
Compare between 🟢probability sampling and 🟠 Nonprobability sampling
🟢probability sampling
1- usually more representative معبرة و ممثلة اكثر عن ال population
2- each member of population has a known (non zero) chance of inclusion
3- less likely to be biased sample بيها تحيز قليل
4- more generalizable يمكن تعميم نتائجها على ال population
🟠Nonprobability sampling
1- Usually less representative
2- Every member of the population has
unknown chance of inclusion
3- MORE likely to be biased
4- LESS generalizable
Types of Probability Sampling
Simple Random Sampling
Systematic Sampling
Stratified Sampling
Cluster Sampling
Multistage Sampling
Simple Random Sampling
A probability sample in which every member of a
study population has been given an equal chance of
selection
How we can establish a sample frame in simple random sampling
1- Is a list of elements that you draw a sample
from.
2- A number is assigned to each element
Numbers are randomly selected into the sample
Tools to select samples from the given sampling frame, these are
lottery method,
Random number (they are available in the appendix of many research methods and
statistics textbooks)
Computer generated random number
Systematic sampling
A probability sampling procedure that involves
selecting every kth element from a list of
population elements, after the first element has
been randomly selected
Selection interval (kth element)
Selection interval (kth element)
The distance between the elements
selected in a sample
Stratified sampling
A probability sampling procedure that involves dividing
the population into groups or strata defined by the
presence of certain characteristics and then random
sampling from each stratum
