AP Stats Unit 4 vocab

Population

entire group you would like to study or draw a conclusion about

Parameter

Any numerical value that comes from the population

Census

study of an entire population

Statistic

any numerical value that comes from a sample

Sample

part of the population from which you take data.

Simple random sample (SRS)

every individual and every group has an equal chance of being chosen. Number list of possible subjects. Describe how to complete randomization using a random digit table. For each chosen number, write down name of corresponding subject. Ignore repeats. Continue until you have a list n subjects.

Stratified random sample

ensures subjects from each subgroup are in the sample. randomly chooses one or more groups to be the sample. the subjects in each group should be different, but each group should be similar with respect to a characteristic that may be related to the response variable.

Example of stratified randomized sample

when investigating average amount of time spent on homework each night, the straits could be freshmen, sophomores, juniors, and seniors. Then your sample would be sure to have students from each grade level since grad level is probably related to average homework time

Cluster Sample

used when many groups are similar to each other. Randomly choose one of more groups to be the sample. Subjects in groups should be different but each group should be similar to every other group

example of cluster sample

if each 4th grade class in an elementary school has students of all ability levels and all socioeconomic groups, the randomly choosing one class as a sample would give an acceptable representation of the fourth grade as a whole

convenience sample

asking whomever you happen to run into. Not a good way from randomization but is quick and easy

systematic random sample

choosing every __ person through a door or on a list

Bias

occurs when a study systematically favors one outcome over another. Can occur when a certain group is over or underrepresented or when the measurement device impacts the results

voluntary response

bias occurs when subjects voluntarily choose to be in the sample, and people usually volunteer only if they have strong motivation

undercoverage

occurs when some groups of people are ignored when the sample is being chosen. A survey sent by email ignores people without access to email

Non-response

bias occurs when one group of subjects having something in common do not answer.

example of non-response

only people with a lot of time on their hands respond

Response

bias occurs when subjects give incorrect answers, either because they have forgotten details, they are intimidated by the interviewer, or they lie about embarrassing or illegal activities

Experiments

studies in which the researcher imposes a treatment on experimental units. Sometimes different groups are simply compared with one another.

observational design

no treatment assigned or imposed in the study

control group

a group of experimental units that receive no treatment or just a placebo. it is not necessary for a well-designed experiment

experimental units

smallest independent “objects” to which treatments are assigned and on which a response is measured

replication

having multiple experimental units in each treatment group (repeats treatment, not the entire experiment) (trails)

Randomization

randomly assigning units to the treatments. Often the experimental units are not a random sample of the population of interest. It is not a problem with the experimental design, but it may limit the scope of inference for the experimental results. Evens out extraneous variables and make treatment groups that are approximately similar in all respects except for the treatment

Double blind

someone must know which treatment the experimental units are got. Subjects don’t know which treatment they are receiving and anyone who interacts with the subjects shouldn’t know which treatment was given to which subject

confounding variable

affects response variable and is also related to group membership.

blocks

groups of experimental units that are homogeneous with respect to some inherent characteristics that is expected to affect the response to treatments