Module 2

Question 1

What are the four goals that all sampling designs must achieve?

Answer 1

• all sampling units are selectable: every sampling unit in the statisitcal population must have some non zero probability of being included in the sample
• selection is unbiased: selection of a sampling unit cannot depend on any attribute
• selection is independent : selection of a specific sampling unit must not increase or decrease the probability that any other sampling unit is selected
• all samples are possible

Question 2

what is bias?

Answer 2

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

Question 3

What is sampling independence?

Answer 3

Sampling independence is when selection of one sampling unit does not influence the probability that any other sampling unit is selected.

Question 4

How to identify errors in sampling design?

Answer 4

prevent problems at the beginning of a study by evaluating proposed sampling designs against the four criteria/goals

Question 5

What is the primary goal of an observational study?

Answer 5

characterize something about an existing statistical population, collect data from an exisiting statistical population that allows us to investigate relationships among variables

Question 6

what is an observational study?

Answer 6

a study using observations from a statistical population where the investigator has no control over the explanatory variables

Question 7

what is a drawback of an observational study?

Answer 7

• provides a tol for discovering associations, but cannot make statements about whether a factor causes the response you are interested in
• while we can look at relationships among variables, these relationships might not be casual

Question 8

What is the response variable?

Answer 8

Response variable a variable that the investigator is interested in studying as a way to answer a research question

Question 9

What is the explanatory variable?

Answer 9

Explanatory variable a variable that an investigator believes may explain the response variable

Question 10

What are confounding variables

Answer 10

unobserved variables that affect a response variable

Question 11

What are spurious relationships?

Answer 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 spurious

Question 12

What is a simple random survey?

Answer 12

• observational study design
• start by identifying every sampling unit in the statistical population and then selection a random subset of those to be in your sample, each sampling unit has the same probability of being included in your sample

Question 13

What is a stratified survey?

Answer 13

• observational study design
• used when there are subgroups within the statistical population that can influence the study results
• first break the statistical population into strata (a subgroup) and then sample within each strata (each strata has equal weighing in the sample)
• the strata are defined ahead of time by the researcher

Question 14

What is a cluster survey?

Answer 14

• observational study design
• used by researches to remove diversity in the statistical population that is not relevant to the research question
• the idea is to create groups where the non relevant diversity is contained within each group (this group is called a cluster)
• the group is called a cluster, which is selected at random from all possible clusters
• a cluster is the sampling unit and observation unit
• one stage: data are collected from all observation units in a cluster
• two stage: surveys a subset of observation units are randomly selected within each cluster

Question 15

What is a case control survey?

Answer 15

• type of observational study design
• used to compare data between two groups
• case group: contains sampling units with a particular response variable
• control: contains sampling units without the response variable of the case group
• this type of sampling is purposefully baised in that it aims to select sampling units for the case group based on a measured response variable and compare that to the control group

Question 16

what is a cohort survey?

Answer 16

• type of observation study design
• follow sampling units over time, looking for the development of a particular response variable
• the goal is to select a random set of sampling units (simple random survey) and observe their fat over time
• the outcome is unknown when the units are selected
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Question 17

What are retrospective studies?

Answer 17

where the outcome is already known, which comes with an increased risk of spurious relationships if you are selecting groups based on the outcome (ex. case control studies are a good example)

Question 18

what are prospective studies?

Answer 18

one where the outcome is not yet knowm, typically more effort since you need to follow the sampling units for a period of time, suffer less from spurious relationshipgs (Ex. cohort study)

Question 19

what is a cross sectional versus a longitudinal study?

Answer 19

• cross sectional studies are ones that study a response variable at only a single snapshot in time
• longitudinal surveys are ones that study a response variable at multiple points in time

Question 20

what is an experimental study?

Answer 20

Experimental study a study involving a statistical population where the investigator can control the explanatory Variables

Question 21

What is the goal of an experimental study?

Answer 21

to study the effect of one (or more) manipulated variables on one (or more) response variables. You do something differently to one group than the other. are able to establish cause and effect among variables

Question 22

What is a factor?

Answer 22

each manipulated variable in an experimental studt

Question 23

What are the two key things that distinguish an experimental study from an observational one?

Answer 23

• the explanatory variable is manipulated by the researcher in an experimental studt
• sampling units are randomly assigned to each level in each factor, as a result there are two steps where sampling units are selected at random in experimental studies

Question 24

What are levels?

Answer 24

the manipulated value within each factor

Question 25

What is pseudoreplication?

Answer 25

• an error in the design of an experimental study where the observation units are analyzed rather than the sampling units

Question 26

what is control treatment?

Answer 26

• element of experiemental study
• common in experimental studies and is intended as a reference treatment to compare against the treatment levels that alter the explanatory variable
• contains everything that the treatment levels do except the treatment itself

Question 27

what is blocking?

Answer 27

• element of experiemntal study
• analgous to stratified sampling, but for experimental studies
• used to control for variation among the sampling units that is not of interest to the researcher

Question 28

what is blinded?

Answer 28

• element of experimental study
• used in experimental studies ivolving people and refers to a design where the sampling unit (usually a person, but could be a group) does not know what treatment they are bieng exposed to
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Question 29

what is a placebo?

Answer 29

often used in medical trials (experiemntal studies) for the control treatment that helps accomplish a blinded deisgn, has no effect on response variable

Question 30

what is a sham treatment?

Answer 30

similar to a placebo in that it is a method used in control treatments. the purpose is to account for the effect of delivery of a treatment that is not of interest to the researcher