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54 Cards in this Set
 Front
 Back
Observational study

Study in which we observe and measure specific characteristics, but don't attempt to manipulate or modify the subjects being studied.


Experiment

Application of some treatment followed by obervation of its effects on the subjects.


Experimental Units

Subjects in an experiment.


Crosssectional study

study in which data are observed, measured, and collected at one point in time.


Retrospective study

aka: casecontrol
Study in chich data are collected from the past by going back in time (through examination of records, interviews, and so on). 

Prospective Study

aka: longitudinal or cohort
Study of subjects in identified groups sharing common factors (called cohorts), with data collected in the future. 

Confounding

A situation that occurs when the effects from two or more variables cannot be distinguished from each other.


Random Sample

Sample selected in a way that allows every member of the poulation to have the same chance of being chosen.


Simple Random Sample

Sample of a particular size selected so that every possisble sample of the same size has the same chance of being chosen.


Probability Sample

Sampling involves selecting members from a population in such a way that each member has a known (but not necessarily the same) chance of being selected.


Systematic Sampling

Sampling in which every Kth eleent is selected.


Convenience Sampling

Sampling in which data are selected because they are readily available.


Stratified Sampling

Sampling in which samples are drawn from each stratum (class).


Cluster Sampling

Dividing the population area into sections (or clusters), then randomly selecting a few of those sections, and then choosing ALL the members fro those selected sections.


Sampling Error

Difference between a sample result and the true population result; results from chance sample fluctuations.


Nonsampling Error

Errors from external factors not related to sampling.


Frequency Distribution

aka: Frequency Table
Listing of data values (either individually or by groups of intervals), along with their corresponding frequencies (or counts). 

Lower class limits

Smallest numbers that can actually belong to the different classes in a frequency distribution.


Upper class limits

Largest numbers that can belong to the different classes in a frequency distribution.


Class boundaries

Values obtained from a frequency distribution by increasing the upper class limits and decreasing the lower class limits by the same amount so that there are no gaps between consecutive classes.


Class midpoints

In a class of a frequency distribution, the value midway between the lower class limit and the upper class limit.


Class width

The difference between two consecutive lower class limits in a frequency distribution.


CVDOT:
Center 
A representative or average value that indicates where the middle of the data set is located.


CVDOT:
Variation 
A measure of the amount that the data vlaues vary amoung themselves.


CVDOT:
Distribution 
The nature or shape of the distribution of the data (such as bell shaped, uniform, or skewed).


CVDOT:
Outliers 
Sample values that lie very far away from the vast majority of the other sample values.


CVDOT:
Time 
Changing characteristics of the data over time.


CVDOT

Center, Variation, Distribution, Outliers, Time


Relative Frequency Distribution

Variation of the basic frequency distribution in which the frequency for each class is divided by the total of all frequencies.


Cumulative Frequency Distribution

Frequency distribution in which each class and frequency represents cumulative data up to and including that class.


Normal distribution

Bellshaped probability distribution.


Arithmetic mean

Sum of a set of values divided by the number of values; usually referred to as the mean.


measure of center

Value intended to indicate the center of the values in a collection of data.


mean

The sum of a set of values divided by the number of values.


median

Middle value of a set of values arranged in order of magnitude.


mode

Value that occurs most frequently.


midrange

Onehalf the sum of the highest and lowest values.


RoundingOff Rule

Carry one more decimal place than is present in the original set of values.


skewed

Not symmetric and extending more to one side than the other.


symmetric

Property of data for which the distribution can be divided into two halves that are approximately mirror images by drawing a vertical line through the middle.


range

The measure of variation that is the difference between the highest and the lowest values.


standard deviation

Measure of variation equl to the square root of the variance.


variance

Measure of variation equal to the square of the stanard deviation.


empirical rule

Rule that uses standard deviation to provide information about data with a bellshaped distribution.


coefficient of variation (CV)

The ratio of the standard deviation to the mean, expressed as a percent.


Range Rule of Thumb

Rule based on the principle that for typical data sets, the difference between the lowest typical value and the highest typical value is approximatley 4 standard deviations (4s)


s

SAMPLE standard deviation


POPULATION standard deviation

define


POPULATION variance

define


SAMPLE variance

define


Exploritory data analysis

EDA
Branch of statistics emphasizing the investigation of data 

5number summary

Minimum value, maximum value, median, and the first and third quartiles of a set of data


boxplot

aka: boxandwhisker diagram
Graphical representation of the spread of a set of data (5# summary). 

Relative Frequency Approxiation of Probability

P(A) = number of times A occurred / number of times the trial was repeated
