Lecture 2 - Sampling

Question 1

define sampling

Answer 1

predetermined procedure for the selection, withdrawal, preservation, transportation, and preparation of the portions to be removed from a lot as samples

Question 2

why do we sample?

Answer 2

• save $$$

- difficult logistics of large populations

Question 3

the set of all objects in the system being investigated

Answer 3

population

Question 4

a portion selected from a large quantity of material

or a unit taken from the total amount of food

Answer 4

sample

Question 5

a sample prepared for testing or analysis

Answer 5

laboratory sample

Question 6

a quantity of bulk material of similar composition whose properties are under study

Answer 6

lot

Question 7

quantity of food that is known or assumed to be produced under uniform conditions

Answer 7

batch

Question 8

each discrete, identifiable portion of food that are suitable for removal from a population as samples that can be individually describes, analyzed or combined

Answer 8

unit

Question 9

the degree to which a property or substance is randomly distributed throughout a propulation

Answer 9

homogeneity

Question 10

an individual portion of material collected by a single operation of a sampling device

Answer 10

increment

Question 11

accurate sampling is important to avoid what kind of risks?

Answer 11

consumer risk, producer risk

Question 12

what is consumer risk?

Answer 12

accepting defective product

Question 13

what is producer risk?

Answer 13

rejecting an acceptable product

Question 14

_____ error arises when a sample is not representative of the population

Answer 14

sampling

Question 15

_____ error arises because of some other reasons

Answer 15

non-sampling

Question 16

______ is an estimate of the uncertainty

Answer 16

variance

Question 17

______ ______ is a function of the sum of variances associated with each step

Answer 17

total variance

Question 18

what are the probability sampling plans?

Answer 18

• simple random sampling
• stratified sampling
• cluster sampling
• composite sampling
• systematic sampling

Question 19

what are non-probability sampling plans?

Answer 19

• judgment sampling
• convenience sampling
• restricted sampling
• quota sampling

Question 20

every unit in a population having a known and equal chance of being selective is representative of what category of sampling plan?

Answer 20

probability sampling plan

Question 21

what motivates the use of a probability sampling plan? (4)

Answer 21

• provides statistically sound basis for obtaining representative samples
• eliminate human bias
• scientific, operationally convenient and simple in theory
• best methods to achieve a representative sample

Question 22

describe simple random sampling

Answer 22

• population N must be known
• random selection process
  ~ simple, high prob of being representative
  ~ IDing all units of the pop can be difficult

Question 23

describe stratified sampling

Answer 23

• divides pop into mutually exclusive subgroups then uses simple random sampling to choose units from each stratum
  ~ more homogenous data, administrative convenience, lower cost, smaller variances for sample sizes
  ~ potential classification error
  ~ prior knowledge of composition and distribution of population; tedious

Question 24

describe cluster sampling

Answer 24

• pop divided into clusters designed to be as similar as possible; randomly selected clusters sampled
  ~ less costly than simple/stratified
  ~ higher sampling error

Question 25

describe systematic sampling

Answer 25

- first unit selected at random from the first k population units and then units are taken every nth unit ~ highly representative, very informational ~ not as random

Question 26

describe composite sampling

Answer 26

- samples drawn from different units in a pop are pooled for analysis

Question 27

the technique where the odds of any unit being selected for a sample cannot be calculated since the selection is based on nonrandom procedures refers to _____ sampling plans

Answer 27

non-probability

Question 28

when would non-probability sampling be appropriate?

Answer 28

checking for adulteration

Question 29

describe judgment sampling

Answer 29

dependent on subjective judgment of the person who is drawing the samples

Question 30

describe convenience sampling

Answer 30

- selecting only accessible part of pop | - aka chunk or grab sampling

Question 31

describe restricted sampling

Answer 31

used when the entire pop is not accessible

Question 32

describe quota sampling

Answer 32

- pop divided into groups; samples are chosen based on experience and judgment (sampling from groups representing various categories)

Question 33

what 4 factors affect the choice of sampling plan?

Answer 33

- purpose of inspection - nature of population - nature of product - nature of test method

Question 34

what's attribute sampling?

Answer 34

- based on whether or not sample possess a certain characteristic (discrete)

Question 35

what's variance sampling?

Answer 35

- estimate quantitatively the amount of a substance or a characteristic (continuous)

Question 36

what type of sampling is this: trained person randomly picks sample/location from sample lot/liquid container as specified by the approved standard method

Answer 36

manual sampling

Question 37

what type of sampling is this: performed mechanically

Answer 37

continuous sampling

Question 38

what 3 criteria determine sample size?

Answer 38

- level of precision - level of confidence (risk) - degree of variability among the population for the attributes beingmeasured

Question 39

write the sample size formula for an unknown population

Answer 39

okay

Question 40

write the sample size formula for a known population

Answer 40

aight