module 2

Question 1

what is the point of sampling design

Answer 1

• to have good rep of a stat population

Question 2

bias

Answer 2

an over- or under-estimate of some value from an average sample compared to the statistical population

Question 3

4 goals of an ideal sampling design

Answer 3

• all sampling units are selectable/can be included
• selection of sampling units are unbiased
• selection must be independent, not influence other selection
• all samples are possible (all samples from sampling units are options)

Question 4

what is an easy approach to avoid bias?

Answer 4

• assign all sampling units a number and find your sample by randomly generating a set of numbers

Question 5

Sampling independence

Answer 5

• selection of one sampling unit doesnt influence the probability that other sampling units are selected

Question 6

observational study def, goals, limitation

Answer 6

• researchers have no influence
• characterize smth abt an existing stat population
• cannot make statement of causes, only correlation/association

Question 7

why cant observational studies give the cause?

Answer 7

• there is no way of knowing if there are other variables that weren’t measured that affect the outcome
• confounding variables

Question 8

response variable

Answer 8

• the response you are interested in

Question 9

explanatory variable

Answer 9

• the factor you investigate

Question 10

confounding variables

Answer 10

• unobserved variables that affect the response variable

Question 11

When the relationship between an explanatory variable and response variable is thought to be driven mostly by a confounding variable, the relationship is called ________.

Answer 11

• spurious

Question 12

5 observational study designs

Answer 12

• simple random survey
• stratified survey
• cluster survey
• case-control survey (outcome is known, other differences are observed)
• cohort survey

Question 13

simple random survey

Answer 13

• sampling unit randomly selected from stat population

Question 14

stratified survey

Answer 14

• taking potential influence into account
  -break stat population into strata and sample each strata
• sampling units are selected from within predefined groups

Question 15

cluster survey

Answer 15

• removes heterogeneity in stat population
• create groups (clusters) where non-relevant heterogeneity is contained
• the cluster is the sampling unit and the observation unit is nesting inside the cluster
• one stage=data collected from all observation units in a cluster
• two stage= randomly selected within a cluster

Question 16

case-control survey

Answer 16

• outcome is known, other differences are observed
• 1st group= case, contains sampling units with particular responsive variable
• ## 2nd group= control, sampling unit but no responsive variable, biased

Question 17

cohort survey

Answer 17

• follow sampling units overtime
• simple random survey but over time

Question 18

strata

Answer 18

• subgroup within stat population

Question 19

retrospective vs prospective studies

Answer 19

• retro=outcome is known ex case control
• pro=outcome is not known ex cohort

Question 20

cross-sectional vs longitudinal studies

Answer 20

• cross-sectional: one point in time only
• longitudinal: many points in time

Question 21

experimental study def and goal

Answer 21

• involving stat population, investigator controls variable(s)
• goal: study the effect of one (or more) manipulated variables on one (or more) response variables

Question 22

manipulated variables are aka ____

Answer 22

factors, one level doesn’t have it the second does

Question 23

t or f: the only difference between experimental and observation studies is that the explanatory variable is manipulated by the researcher

Answer 23

f: that sampling units are randomly assigned to each level in each factor for experimental

Question 24

________ is the cornerstone of experimental studies

Answer 24

Replication

Question 25

Replication

Answer 25

• the idea that treatment (manipulation) will be repeated many times to see how repeatable a measured outcome is
• the number of sampling units

Question 26

error in experimental studies

Answer 26

• pseudoreplication
• observation units are analyzed rather than the sampling units

Question 27

common design elements of experimental studies

Answer 27

• control treatment (reference treatment to compare against the treatment levels that alter the explanatory variable)
• blocking (control for variation among the sampling units that is not of interest to the researcher)
• placebo
• blinded (sampling unit doesn’t know which treatment they are exposed to
  sham treatment