Stats Vocab

placebo

a dummy treatment with no active ingredients

table of random digits

a long string of digits ranging from 0 to 9 and are independent of each other

predictive validity

a measurement that can be used to predict success on tasks that are related to the property measured

parameter

a number that describes the population, a fixed number but we don't know the actual value

seasonal variation

a pattern that repeats itself at regular known intervals

measure

a property of a person or thing when we assign a number to represent the property

lurking variable

a variable that has an important effect on the relationship among the variables in a study but is not one of the explanatory variables studied

completely randomized

all the experimental subjects are allocated at random among all the treatments

double blind

an experiment in which neither subjects nor physicians recording the symptoms know which treatment was received

randomized comparative experiment

an experiment that compares just two treatments

outlier

an individual observation that falls outside the overall pattern of the graph

statistically significant

an observed effect of size that would rarely occur by chance

nonsampling error

are errors not related to the act of selecting a sample from the population, can be present in the census

variance

average squared distance

midpoint

center of distribution

voluntary response sample

chooses itself by responding to a general appeal

average

combining multiple measurements to get a more reliable result

matched pairs design

compares just two treatments

simple random sample

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

five-number summary

consists of the smallest observation, the first quartile, the median, the third quartile, and the largest observation

experiment

deliberately imposes some treatment on individuals in order to observe their responses

variability

describes how spread out the values of the sample statistics are when we take many samples

quartiles

divide the information into quarters

sampling errors

errors caused by the act of taking a sample, cause sample results to be different from the results of a census

exhaustive

every individual appears in some class

seasonally adjusted

expected seasonal variation is removed before the data are published

clinical trails

experiments that study the effectiveness of medical treatments on actual patients

qualitative data

expressed in qualities

quantitative data

expressed with numbers

rate

fraction, proportion, percentage

histogram

graph of the distribution of a quantitative variable

block

group of experimental subjects that are known before the experiment to be similar in some way that is expected to affect the response to the treatment

subjects

individuals studied in an experiment

boxplot

is a graph of the five-number summary

probability sample

is a sample chosen by chance

census

is a sample survey that attempts to include the entire population in the sample

mean x

is a set of observations is their average

response

is a variable that measures an outcome or results of a study.

explanatory variable

is a variable that we think explains or causes changes in the response variable

variable

is any characteristic of an individual

treatment

is any specific experimental condition in applied to the subjects

bias

is consistent repeated deviation of the sample statistic from the population parameter in the same direction when we take many samples

random sampling error

is the deviation between the sample statistic and the population parameter caused by chance in selecting a random sample

population

is the entire group of individuals about which we want information

nonresponse

is the failure to obtain data from an individual selected for a sample

median

is the midpoint of a distribution, the number such that half the observations are smaller and the other larger

sample

is the part of the population from which we actually collect information and is used to draw conclusions about the whole

sampling frame

list of individuals from which we will draw our samples

trend

long term upward or downward movement

confidence statement

margin of error and level of confidence

valid

measure of a property if it is relevant or appropriate as a representation of that property

standard deviation s

measures the average distance of the observations from their mean

processing errors

mistakes in mechanical tasks such as doing arithmetic or entering responses into a computer

exclusive

no individual is in more than one class

statistic

number that describes a sample, value is known but can change from sample to sample

data

numbers with a context

observational study

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

response error

occurs when a subject gives an incorrect response

undercoverage

occurs when some groups in the population are left out of the process of choosing the sample

skewed

one side extends much farther than the others

categorical variable

places an individual into one of several groups or categories

line graph

plots observations against time at which it was measured

random error

repeated measurements on the same individual give different results

level of confidence

says what percentage of all possible samples satisfy the margin of error

convenience sampling

selection of whichever individuals are easiest to reach

pie charts

show the whole divided into parts

bias

statistical study systematically favors certain outcomes

dropouts

subjects who begin the experiment but do not complete it

nonadherers

subjects who participate but don't follow the experimental treatment

sample survey

survey some group of individuals by studying only some of its members

quantitative variable

takes numerical values for which arithmetic operations such as adding and averaging make sense

confounded

the effects on a response variable cannot be distinguished from each other

individuals

the objects described by a set of data. may be people, animals, or things

margin of error

the percentage that tells us how close our estimate comes to the truth 1/square root (n)

block design

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

symmetric

the right and the left sides of the histogram are approximately mirror images

statistics

the science and art of data

stemplot

used for small data sets and is quicker and presents more detailed information

response variable

variable that measures an outcome or result of a study

distribution

what values a variable takes and how often it takes these values

unit

what we measure in and record the measurements

instrument

what we use to make a measurement