# Stats Randomness

## 52 terms · :P

### randomness

our greatest enemy and our most important tool

### simulation

a sequence of random outcomes that model a situation; an artificial representation of a random process used to study long term effects

### component

the most basic situation in a simulation in which something happens at random

### outcome

an individual result of a component

### trial

the sequence of several components representing events

### response variable

the result of each trial with respect to what we were interested in

### population

the entire group of individuals or instances about whom we hope to learn

### sample

a (representative) subset of a population, examined in hope of learning about the population

### sample survey

a study that asks questions of a sample drawn from some population in the hope of learning something about the entire population; a poll

### statistic

any summary calculated from the sampled data (Latin)

### parameters

key numbers in math models used to represent reality (Greek)

### population parameter

a numerically valued attribute of a model for a population, often unknowable and estimated from sampled data

### sample statistic

estimated population parameter

### representative sample

Statistics computed from it accurately reflect the corresponding population parameters

### bias

Any systematic failure of a sampling method to represent its population

### voluntary response

individuals choose whether to respond on their own

### convenience

when the sample is comprised of individuals readily available

### under coverage

when individuals from a subgroup of the population are selected less often than they should be

### non response

when a large fraction of those sampled do not respond

### response bias

when respondents' answers may be affected by survey design

### reducing bias

often the best use of time and resources when sampling or surveying

### randomization

the best defense against bias

### simple random sample (SRS)

a sample in which each set of n elements in the population has an equal chance of selection; the standard method of randomization

### sampling variability

the natural tendency of randomly drawn samples to differ from each other

### sample size

what the precision of the statistics of a sample depend on

### census

a sample that consists of the entire population

### sampling frame

a list of individuals, which defines but may not be representative of the entire population, from which the sample is drawn

### stratified samples

these can reduce sampling variability by identifying homogeneous subgroups and then randomly sampling within each

### cluster samples

these randomly select among heterogeneous subgroups that each resemble the population at large, making our sampling tasks more manageable

### systematic samples

these are samples of a certain order; these work when there is no relation b/t the order of the sampling frame and the variables of interest

### multistage sample

a scheme that combines several sampling methods

### observational study

a study based on data in which no manipulation of factors has been employed

### retrospective

Subjects are selected and then their previous conditions or behaviors are determined

### prospective

Subjects are followed to observe future outcomes

### a valid experiment

to prove a cause-and-effect relationship, we need to perform

### an experiment

manipulates factor levels to create treatments, randomly assigns subjects, compares the responses of the subject groups

### factor

a variable whose levels are controlled by the experimenter

### levels

specific values that the experimenter chooses for a factor

### treatment

process, intervention, or other controlled circumstance applied to randomly assigned experimental units

### experimental units

individuals on whom an experiment is performed

### response

a variable whose values are compared across different treatments

### control, randomize, replicate, block

principles of experimental design

### control group

the group of experimental units assigned to a baseline treatment level (default or placebo)

### statistically significant

when an observed difference is too large for us to believe it is likely to have occurred by chance

### placebo

A (fake) treatment known to have no effect, administered so that all groups experience the same conditions

### placebo effect

The tendency of many human subjects (often 20% or more of experimental subjects) to show a response even when administered a placebo

### blinding

Individuals associated with an experiment are not aware of how subjects have been allocated to treatment groups

### block

Group together subjects for experiments that are similar and randomize within those groups as a way to remove unwanted variation (parallel treatments on different groups); like stratifying

### matching

in a retrospective or prospective study, subjects who are similar in ways not under study may be paired and then compared with each other on the variables of interest as a way to reduce unwanted variation

### randomized, comparative, double-blinded, placebo-controlled

the best experiment

### lurking variable

Creates an association between two other variables that tempts us to think that one may cause the other

### confounding variable

some other variable associated with a factor has an effect on the response variable