Lecture 13 9/19/24

Question 1

What are the potential sources for data collection?

Answer 1

-total population/census
-designed/formal sample
-non-designed/informal sample

Question 2

What are the advantages and disadvantages of collecting data from a total population?

Answer 2

advantages:
-true picture
disadvantages:
-too expensive
-time consuming
-not always practical

Question 3

What are the advantages and disadvantages of collecting data from a sample?

Answer 3

advantages:
-less costly
-saves time
-more practical
disadvantages:
-may not truly represent population

Question 4

What are primary data samples?

Answer 4

information collected directly by an investigator for their specific study, such as through survey or observational study

Question 5

What are secondary data samples?

Answer 5

samples are taken from existing data or previously collected by someone else

Question 6

What are the general considerations for sampling?

Answer 6

-objectives of the study
-target population
-what to measure/how much to measure
-precision
-sampling units
-variables
-population characteristics
-practicality
-cost and time

Question 7

What are the criteria for the acceptability of sampling method?

Answer 7

-each individual unit has equal chance of selection
-representative of the population sampled
-measurable validity
-feasible
-economical and efficient

Question 8

What are the characteristics of non-probability sampling?

Answer 8

-no scientific/explicit approach
-mostly used in analytical studies
-selection bias likely but often unknown
-no mathematical property

Question 9

What are the types of non-probability sampling?

Answer 9

-judgement: experts select units to include
-convenience: units that are easy to obtain are included
-purposive: units are chosen based on some attributes

Question 10

What are the characteristics of probability sampling?

Answer 10

-scientific approach
-used in descriptive and analytical studies

Question 11

What is the required information for probability sampling?

Answer 11

-sampling fraction: proportion of population to be included in sample
-sampling frame: list of all sampling units in source population
-sampling unit: basic elements of the population that is sampled

Question 12

What is simple random sampling?

Answer 12

-every individual in the source population has equal probability of being included
-complete list of the sampling frame

Question 13

What are the advantages and disadvantages of simple random sampling?

Answer 13

advantages:
-equal probability of selection
-able to calculate confidence intervals
disadvantages:
-bias if population is not homogenous
-difficult if sampling frame cannot be defined

Question 14

What are the characteristics of stratified random sampling?

Answer 14

-used when population is not homogenous for characteristics of interest
-ensures that each group in the population is represented

Question 15

What is the procedure for stratified random sampling?

Answer 15

-identify sampling frame
-sort into strata
-select a simple random sample within each stratum

Question 16

Why is stratified random sampling used?

Answer 16

-provides proportional representation to every strata
-ensures that individuals from smaller strata of the population are included in sufficient numbers

Question 17

When can stratification occur?

Answer 17

-during sampling
-during analysis

Question 18

What are the advantages and disadvantages of stratified random sampling?

Answer 18

advantages:
-more flexible than SRS
-improves precision
disadvantages:
-must know which stratum each subject belongs to prior to sampling

Question 19

What are the characteristics of systematic random sampling?

Answer 19

-also known as interval sampling
-fixed percentage of the population is selected at equal intervals
-complete list of sampling frame is not necessary

Question 20

What is the procedure for systematic random sampling?

Answer 20

-sampling interval j is calculated as the study population size divided by the required sample size
-first unit is randomly chosen, and every jth study subject after that is included in the sample

Question 21

What are the advantages and disadvantages of systematic random sampling?

Answer 21

advantages:
-easy and practical
-does not require knowledge of total population size or sampling frame
-ensures that sampling units are distributed evenly over entire pop.
disadvantages:
-characteristics being estimated may be related to interval itself
-difficult to assess variability of estimates

Question 22

When is cluster sampling used?

Answer 22

-when identification of the sampling frame is impractical and/or too costly
-when observation units are aggregated into larger sampling units

Question 23

What is the procedure for cluster sampling?

Answer 23

take a simple random sample of the population of clusters, which is used to estimate the measure of all observational units within each cluster

Question 24

What are the advantages and disadvantages of cluster sampling?

Answer 24

advantages:
-practical
-cheaper than simple random sampling
-flexible
-works great in homogenous pop.
disadvantages:
-requires larger sample size to obtain same precision as simple random sampling

Question 25

What are the characteristics of multi-stage sampling?

Answer 25

-sampling occurs are multiple stages
-different sampling methods can be used at different stages

Question 26

What are the advantages and disadvantages of multi-stage sampling?

Answer 26

advantages:
-practical
-cheaper
-flexible
disadvantages:
-requires larger sample size to obtain same precision as simple random sampling