stats unit 1 part 2

Population

The entire group of items/individuals that we want information about

Parameter

A number that describes some characteristic of a population

Census

An attempt to contact every item/individual in the entire population

Sample

A subset of the population from which we collect data

Statistic

A number that describes some characteristic of a sample

Observational unit

An item/individual described in a data set or statistical study

Variable

A characteristic that can take different values for different observational units

Investigative question

The question formulated FIRST in a study; it guides data collection, guides the choice of analysis methods, and indicates the type of conclusions that can be made. Components: variable(s), type of inference, type of conclusion

Experiment

A study where we deliberately impose a treatment on individuals to observe their responses; includes random assignment of subjects to treatment groups

Experimental units (subjects/participants)

The individuals/items that treatments are imposed on in an experiment

Response (dependent) variable

A variable that measures an outcome of a statistical study

Explanatory (independent) variable / factor

A variable that may help explain or predict changes in a response variable

Levels

The possible values of a factor (each one is a treatment)

Observational study

A study where we observe individuals and measure variables of interest but do NOT impose treatments

Retrospective study

An observational study where data about the units are gathered from the PAST

Prospective study

An observational study where data are gathered at a select point in time and into the FUTURE

Survey

An observational study in which data are collected from people by asking them a common set of questions

Extraneous variable

A variable other than the explanatory variable that may have an effect on the response variable

Confounding variable

An extraneous variable associated with BOTH the explanatory and response variables; makes it hard to tell whether the explanatory variable causes changes in the response

Random sampling

Using a chance process to determine which members of a population are chosen for the sample

Statistically significant

When an observed difference in responses between groups is so large that it is unlikely to be explained by chance variation in the random assignment

Randomization distribution

The distribution of a statistic generated by repeatedly reassigning the response values to treatment groups

Random selection

allows generalization of results to the population they were chosen from

Informed consent

Participants must agree to take part, knowing what the study involves, before data collection

Confidentiality

Individual data are kept private and only group statistical summaries are made public

strata

groups of individuals that share characteristics thought to be associated with the variables being measured in a study

stratified random sample

selected by choosing an SRS from each stratum and combining the SRSs into one overall sample

simple random sampling

every group of n individuals in the population has an equal chance to be selected as the sample.

clusters

groups of individuals that are located near each other

Cluster random sample

selected by choosing an SRS of clusters and including each member of the selected clusters in the sample

Systematic random sample

selected from an ordered arrangement of the population by randomly selecting one of the first k individuals in the population and choosing every kth individual thereafter

Convenience sample

consists of members of the population that are EASY to reach

Bias

resulting sample statistic is likely to under/overestimate the population parameter due to a flaw in the data collection process

Voluntary response sample

consists of people who CHOOSE to be in the sample by responding to a general invitation

Undercoverage

when some members of the population are less likely to be chosen or cannot be chosen for a sample

Nonresponse

when an individual chosen for the sample cannot be contacted or refuses to participate

Response bias

when responses to a survey question consistently differ from the truth in the same way

double-blind

an experiment where neither the subjects nor those interacting with them and measuring the response variable know which treatment a subject is receiving

single-blind

an experiment where either the subjects or the people interacting with them and measuring the response variable don’t know which treatment a subject is receiving

random assignment

the treatments are assigned to experimental units (or experimental units are assigned to treatments) using a chance process

replication

multiple experimental units are assigned to each treatment

direct control

keeping the values of some extraneous variables the same for all experimental units

block

a group of experimental units that are known before the experiment to be similar in some way that is expected to affect the response to the treatments

Randomized Block Design

the random assignment of experimental units to treatments is carried out separately within each block so all treatment occur within each block