stats chapter 4

3 principles of statistical design

control, random assignment, replication

experiment

deliberately imposes some treatment on individuals to measure their responses

cluster sample

divide the population into groups/clusters. Randomly select some of these clusters. ALL individuals in the chosen clusters are included in the sample

how to store a variable

enter a random number, sto, math 1, enter sto, math 8

completely randomized design, block, matched pair

experimental design

explanatory variable

factors, may help or explain or influence changes in a response variable

systematic error that tends to occur in the same direction whenever you use this sampling method

bias is any

replication

certain number of subjects in each group

convenience sample

choosing individuals who are easiest to reach, uses bias and unlikely to represent the whole population

matched pairs design

common form of blocking for comparing just two treatments

response variable

measures an outcome of a study

nonsampling error

mistakes that occur after taking a sample

observational study

observes individuals and measures variables of interest but does NOT attempt to influence the responses

undercoverage

occurs when some groups in the population are left out of the process of choosing the sample (ex a sample of all households in an area leaves out the homeless, UNDERESTIMATE)

confounding

occurs when the two effects of variables cannot be separated, caused by lurking variables

simple random sample (SRS)

of size n consists of n individuals from the population chosen in such a way that every set of n individuals has an equal chance to be the sample actually selected

the results may be affected by response bias

32% say that they favor some kind of national proficiency test example

example of response bias

people lying and saying they voted when they didn't

only people aged 8-28 in Massachusetts

A company wishes to determine which of two video game systems is preferred. A large SRS of people aged 8-28 living in Massachusetts was surveyed to determine this. What population can the results of this survey be safely generalized?

voluntary response sample

A sample which involves only those who voluntary participate in the sampling, biased because it attracts passionate people, leads to an OVERESTIMATE

stratified random sample

First divide the population into groups of similar individuals, called strata. Then choose a separate SRS from EACH stratum to form the full sample.

sampling error

Mistakes made in the process of taking a sample that could lead to inaccurate information about the population. Bad sampling methods and undercoverage are common types of sampling error.

inference about cause and effect

randomly assigned

describe how you will select your sample

Put labels, look for 1 digit/2 digits in the table within my labels (inclusive). I will ignore repeats. I will be done when I have x people

which of the following is a true statement about experimental design

Randomization is a key component in experimental design. Randomization is used to reduce bias.

inference about population

randomly selected

simple random sample, stratified random sample, cluster random sample

sampling methods

A professor wants to study the effectiveness of a new study tool for a course. There are 150 students registered for the course.The professor assigns each student a number from 1 to 150 and uses a random number generator to assign the first 75 students selected to use the new study tool. The remaining 75 subjects are assigned to use the previous study tool.What type of experiment design is this?

completely randomized

a cause and effect relationship between two variables can best be determined from which of the following

a controlled experiment where the observation units are chosen randomly

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

gives every possible sample of the same size the chance to be selected

a simple random sample is a sample that

treatment

a specific condition applied to the individuals in an experiment

response bias

a student tells each subject her personal opinion opposing marijuana, and then asks them their opinion. What is the existing flaw in the experimental design?

lurking variable

a variable that is not among the explanatory or response variables in a study but that may influence the response variable, makes it hard to see the true relationship between the explanatory and response variables

single blind experiment

an arrangement in which participants remain unaware of whether they are in the experimental group or the control group, but they know theres 2 groups

double blind experiment

an experiment in which neither the subjects nor the researchers know which subjects are members of the experimental group and which are serving as control subjects, until after the experiment is over.

statistically significant

an observed effect so large that it would rarely occur by chance

all planned studies must be reviewed in advance by an institutional review board, all subjects must give their informed consent, and all individual data must be kept confidential

basics of data ethics

nonresponse bias

bias introduced when a large fraction of those sampled fails to respond

bias

systematically favors certain outcomes

completely randomized design with two explanatory variables

the 30 second and 60 second commercial example

census

the official count of a population

randomized block design

the random assignment of experimental units to treatments is carried out separately within each block

placebo effect

the response to a dummy treatment

experimental units

the smallest collection of individuals to which treatments are applied

completely randomized design

the treatments are assigned to all the experimental units completely by chance

what is the purpose of using a control group

to provide a baseline for comparing the effects of the other treatments

when is it beneficial to use a blocked design

when a population consists of groups of individuals that are similar but different

when does randomization take place in a block design

when there's a lurking variable