Lecture 5: Sampling Flashcards
(52 cards)
Why should we sample? The number of all ______ observations is often too great, or even infinite. Samples can be used to infer population statistics based on the CLT
POSSIBLE
T/F: samples must be drawn with care to ensure that it is an unbiased representation of the population
true
This explains WHY many statistical models work, even when the data doesn’t form a normal distribution.
The Central Limit Theorem
There are parts to the explanation of the CLT, can you tell me what they are?
1) n = 1000
2) n = >30
3) normal distribution
1) start with any population (n = 1000)
2) take repeated samples (n=>30)
3) as the # of samples taken increases, the distribution oft he sample means will start to resemble a normal distribution, no matter the shape of the original distribution
What are the five steps to the sampling process?
1) define the population
2) construct a sampling frame
3) select a sampling design
4) specify the information to be collected
5) collect data
“Population” is a collection of ___ _______ units of observations (who you want to later generalize about)
a collection of all possible units of observation
Definition: This is a representative list of units/individuals in the population to be sampled from
sampling frame
T/F: the sampling frame should try to include all units in the population (it should try to be EXHAUSTIVE)
True!
T/F: each unit/individual should only appear once in the sampling frame
true
What is a sampling design? (procedure to….)
procedure to select as many units from sampling frame to be in sample. ideally as many as possible (to satisfy the CLT)
How do we specify information to be collected? (Step 4)
Using questionnaires, loggers, instruments, etc. Usually involves a pre-pilot test.
Match this description to the correct step of the sampling process:
“All possible units of observation that you will later generalize about”
Step 1: define the population
Match this description to the correct step of the sampling process:
“Representative list of units/individuals in the population be sampled from”
Step 2: Construct a sampling frame
Match this description to the correct step of the sampling process:
“Procedure to select units from sampling frame to be in sample”
Step 3: Select a sampling design
Match this description to the correct step of the sampling process:
“using questionnaires, loggers, etc. usually involving a pre/pilot test”
Step 4: Specify information to be collected
Match this description to the correct step of the sampling process:
“Go get it! Limit bias as much as possible”
Step 5: Collect data
What are the 4 main categories of PROBABILITY SAMPLING?
Simple random
Systematic
Stratified
Cluster
What are the 4 main categories of NON-PROBABILITY SAMPLING?
Convenience
Volunteer
Snowball
Judgemental
Match the description to the correct sampling method category:
“A sample drawn such that every member of the population has a purely equal chance of being included”
Probability - simple random
Match the description to the correct sampling method category:
“A sample that is selected with numerical or spatial REGULARITY – every nth”
Probability - systematic
Match the description to the correct sampling method category:
“Used when a key characteristic of the population is of interest (program, age, etc.) and you want to ensure a proportionate sized sub-sample of each characteristic group”
Probability - stratified
Match the description to the correct sampling method category:
“Samples drawn from selected categories or quadrats from a very large study area … done to reduce cost and time”
Probability sampling - cluster
Match the example to the correct sampling method category:
“Picking 10 from a hat”
Probability - simple random
Match the example to the correct sampling method category:
“table of random numbers to select the whole sample”
probability - simple random
