Sampling populations

Question 1

What are the two reasons for why how sampling is done is important?

Answer 1

1. Obtaining reliable measurements of the population parameters
2. Assessing the uncertainty of those measurements

Question 2

What were the results of the 1984 study on Feline Hi-Rise syndrome (cats falling out of windows)?

Answer 2

There was a positive correlation between survival and height fallen. Cats that fell from higher stories were more likely to survive

Question 3

What did the vets behind the 1984 study on Feline Hi-Rise syndrome attribute their results to?

Answer 3

1. Cats had a high surface area to volume ratio with their size and leg shape
2. Had excellent vestibular systems
3. They reached terminal velocity quickly, relaxed and were better able to absorb the impact
4. They could land on their feet and absorb the shock through soft tissue

Question 4

What was the problem with the sample in the 1984 study on Feline Hi-Rise syndrome?

Answer 4

It was a sample of convenience. The only cats studied were the ones that fell out of windows by chance and were brought to the vets

Question 5

How was the sample in the 1984 study on Feline Hi-Rise syndrome biased? What were the vets missing?

Answer 5

Only cats that were brought into the clinic were studied. Many cats that fell out of higher floors died and weren’t brought in, and many that fell out of lower floors weren’t injured

Question 6

What is a population?

Answer 6

Every single individual/unit of interest

Question 7

What is a sample?

Answer 7

A subset of units from a population

Question 8

What is a sampling unit?

Answer 8

The basic unit of study. Can be a group or an individual thing

Question 9

What are 3 characteristics of good samples?

Answer 9

1. Independent selection
2. Random selection
3. Sufficiently large

Question 10

What are 3 challenges with sampling?

Answer 10

1. Sampling error
2. Sampling bias
3. Precision

Question 11

What is sampling error?

Answer 11

Departure from the true population parameter due to chance. Is just luck

Question 12

What is the precision of an estimate?

Answer 12

The spread of estimates from sampling error

Question 13

What is precision?

Answer 13

The idea of being reproducible in amount or performance. Estimates are tightly grouped and repeatable

Question 14

Does low sampling error result in high or low precision? High or low reproducibility?

Answer 14

High precision and high reproducibility

Question 15

How do you minimize sampling error?

Answer 15

Increase sample size and take multiple samples

Question 16

What is sampling bias?

Answer 16

A systemic discrepancy between estimates and the true population parameter. A consistent over or underestimation

Question 17

What is accuracy?

Answer 17

How close to the true population parameter the estimate is

Question 18

What is the difference between sampling error and sampling bias in terms of the direction of deviation?

Answer 18

Sampling error deviates in both directions. Sampling bias only deviates in one

Question 19

Does low sampling bias result in high or low accuracy?

Answer 19

High

Question 20

What is measurement error?

Answer 20

Imprecision caused by variation in measurements on an individual due to chance

Question 21

What is measurement bias?

Answer 21

Systemic differences between the truth and the measured value of each individual

Question 22

What are the two criteria for a sample to be random?

Answer 22

1. Every individual has an equal chance to be sampled

2. Independence: sampling one has no effect on another

Question 23

What happens to the sample if every individual isn’t equally likely to be chosen?

Answer 23

Get a biased sample

Question 24

What happens to the sample if there’s no independence?

Answer 24

Smaller sample size and miscalculated precision

Question 25

What would be 2 ways to do a random sample?

Answer 25

Random number generators and random plots

Question 26

What is a sample of convenience?

Answer 26

A sample based on individuals that are easily available to the researcher. Not a good thing to have

Question 27

What is volunteer bias?

Answer 27

A systemic difference in human studies between the pool of volunteers and the population where they came from

Question 28

Why is volunteer bias a thing?

Answer 28

The behaviour of subjects affects their ability to be chosen