V Stats V44

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Observational study

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

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Experiment

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

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Experimental Units

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Subjects in an experiment.

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Cross-sectional study

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

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Retrospective study

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

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Prospective Study

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

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Confounding

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

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Random Sample

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

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Simple Random Sample

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

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Probability Sample

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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.

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Systematic Sampling

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Sampling in which every Kth eleent is selected.

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Convenience Sampling

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

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Stratified Sampling

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

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Cluster Sampling

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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.

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Sampling Error

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

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Nonsampling Error

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Errors from external factors not related to sampling.

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Frequency Distribution

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

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Lower class limits

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

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Upper class limits

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

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Class boundaries

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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.

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Class midpoints

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

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Class width

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

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CVDOT:
Center

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

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CVDOT:
Variation

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

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CVDOT:
Distribution

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

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CVDOT:
Outliers

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

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CVDOT:
Time

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Changing characteristics of the data over time.

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CVDOT

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Center, Variation, Distribution, Outliers, Time

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Relative Frequency Distribution

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

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Cumulative Frequency Distribution

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

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Normal distribution

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Bell-shaped probability distribution.

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Arithmetic mean

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

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measure of center

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

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mean

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

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median

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

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mode

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Value that occurs most frequently.

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midrange

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One-half the sum of the highest and lowest values.

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Rounding-Off Rule

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

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skewed

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

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symmetric

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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.

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range

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

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standard deviation

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

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variance

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

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empirical rule

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Rule that uses standard deviation to provide information about data with a bell-shaped distribution.

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coefficient of variation (CV)

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

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Range Rule of Thumb

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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)

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s

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SAMPLE standard deviation

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POPULATION standard deviation

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define

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POPULATION variance

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define

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SAMPLE variance

Back 50

define

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Exploritory data analysis

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EDA
Branch of statistics emphasizing the investigation of data

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5-number summary

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

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boxplot

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aka: box-and-whisker diagram
Graphical representation of the spread of a set of data (5# summary).

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Relative Frequency Approxiation of Probability

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