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65 Cards in this Set
- Front
- Back
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Definition
Descriptive Statistics |
Serves as a tool to describe or summarize or reduce to manageable form.
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Definition
Quantitative |
Measures of height, weight, time, etc... Dealing with numbers
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Definition
Qualitative |
Gender, college major, type of pet, etc...Dealing with descriptors
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Definition
Inferential Statistics |
Purpose is to predict or estimate characteristics of a population from a knowledge of the characteristics of only a sample of the population
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Definition
Population |
Any group of persons having a defined characteristic
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Definition
Sample |
A portion of the population
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Definition
Variable |
Any observation that can take different values (e.g. gender or race)
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Definition
Attribute |
A specific value on a variable (e.g. female or male)
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Definition
Measurement |
Transforms attributes into more tractable things, numbers.
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What are the Measurement Scales
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Nominal
Ordinal Interval Ratio |
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Definition
Nominal Measurements |
-lowest level of measurements
-Grouping or categorizing with respect to some attribute/quality -Anything that can be placed into a category -Code with numbers |
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Examples
Nominal |
-College Major
-ethnicity -Gender -Eye Color |
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Definition
Ordinal Measurements |
-RANKING
-ranks an attribute -a level above nominal -possible with different amounts of an attribute |
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Examples
Ordinal |
-Class Ranking
-Order of people crossing the finish line -Rank of feeling on a scale |
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Definition
Interval Measurement |
-Describe the size/attribute of the differences amoung things
-Zero= NOT correspond to absence of variable measured |
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Examples
Interval |
-Temperature
-Calendar year |
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Definition
Ratio Measurement |
-Highest level of measurements
-same as interval BUT zero=the absence of the property being measured |
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Examples
Ratio |
-Age
-Height -Weight -distance -Time |
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Definition
Continuous Variable |
A variable that can assume an infinite number of whole and fractional values
e.g. weight, age, & reaction time |
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Definition
Discrete Variable |
A variable where measurement can take on only separated values and can only assume whole numbers
e.g. number of children in the family |
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Definition
Parametric Statistics |
Deals with the use of means and standard deviations and requires that the variables measured be of INTERVAL or RATIO data types
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Definition
Nonparametric Statistics |
Deals with frequency counts or ranking of the measured variable
Requires that the measured variable be NOMINAL or ORDINAL |
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Definition
Independent Variable |
"Grouping"
The experimental variable or the treatment variable. It is manipulated in some manner so it may be described in that manner |
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Definition
Dependent Variable |
Used to describe the varibales being measured or the variable of interest (research/outcome variable)
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Definition
Measures of Central Tendency |
Describe typical, average, or representative scores
Convey info about the center of a distribution of a set of scores Most widely used of all statistical descriptions of data |
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What are the common types of measures of central tendency
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-Mode
-Median -Mean |
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Definition
Mode |
The score or observation that occurs most frequently
-appropriate for ANY variable and may be used with ALL data types (especially with nominal) |
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Definition
Median |
The 50th percentile of a distribution. The midpoint of the distribution
-equal number of observations above and below the median. -You have to rank the scores in order (high-low, low-high, etc...) |
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What can Percentile Rank be used for?
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Often used for establishing things like obesity in growing children
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Definition
Mean |
The arithmetic average of a set of numbers
-every score in the distribution is used in calculating the mean. -most widely used of the central tendency -the foundation for statistical concepts |
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Definition
Trimmed Mean |
A mean calculated with the lowest and highest scores discarded.
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What are the 2 most important statistical characteristics of any distribution of scores
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1)Central Tendency
2)Variablility |
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What are the types of Variability
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-range
-variance -standard deviation |
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Definition
Range |
The difference between the largest and smallest scores in a distribution (and only these two scores)
Problems: Outliers increase ranges & little to no value in inferential statistics |
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Definition
deviation scores |
Reflect something about the degree of variation in a set of scores
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Definition
Sum of Squares |
to square each deviation and then sum the squared deviation scores (instead of working with the absolute value of the deviation scores).
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Definition
Variance |
The mean of the squared deviation scores divided by the degrees of freedom, also known as the MEAN SQUARE
Not very useful in descriptive measure |
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Definition
Degrees of freedom |
Number in the sample minus one. represents the number of scores that are free to vary
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Definition
Standard Deviation |
The square root of the variance.
-Extensively used in descriptive statistics -most commonly used measure of the variability of the scores |
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What is a graph
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A visual representation that are used to describe the characteristics of a distribution of scores
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Definition
Rank Order Distribution |
A method where the scores are put in order from high to low
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Definition
Simple Frequency Distribution |
a method where the frequency of scores at each value of the variable are listed
-Works well when the range of the score is small |
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Definition
Group Frequency Distribution |
a method where the frequency of scores are grouped into classes or intervals
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If the range scores is large which distribution is best?
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Grouped Fredquency Distribution
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How many intervals is best in a data?
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10-20 intervals
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If a range of scores is great how does it affect the intervals?
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More intervals
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What happens when info/data is put is grouped into intervals?
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information loss.. fewer the intervals, the greater the loss
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How many intervals?
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this question is answered by some compromise b/n the importance of precision and the ease of the interpretation for the intended audience
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Once you have a freq. distribution what is the best way to display that data?
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in the form of a table
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most common methods of graphing
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-histogram
-frequency polygon -ogive curve (cummulative freq. polygon) |
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Frequency polygon is..
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similar to a histogram but a line graph is used- data is sometimes presented in the form of presentages
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Cumulative Freq. Polygon
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= Ogive curve
-Principal value of this type of graph is that info is arranged in such a way the percentile rank of any observation can be easily estimated |
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Types of distributions: Normal
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-symmetrical- 50% on each side
- bell shaped -mean, median, mode are equal -if we know the mean & standard deviation, each individual's performance on the dependent variable can be evaluated -numerous variables are normally distributed or approximately so (IQ scores, heightof adult women, etc.) |
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Other types of distributions
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-bimodal
-multomodal -rectangular (no true mode) -skewed distributions (positive/negative) |
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Unimodal distribution
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one mode as in the normal distribution
-mean, median and mode = equal |
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bimodal distriubtion
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two modes in distribution
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multimodal
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three or more modes
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in skewed distributions what happens to the mean?
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-positively skewed- mean will be larger than the median or mode
-Negatively skewed- mean will be smaller than the median or mode |
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In skewed distributions where is the median?
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between mode and mean (usually closer to the mean)
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What incr. as the magnitude of the skewdness increase?
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-degree of symmetry
-differ among mena, median & mode |
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Skewedness = ?
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3(Mean- Median)/standard devitaion
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Kurtosis
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measure of reltive peakedness in a curve
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Platykuric
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flat, broad
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Leptokuric distribution
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slender, narrow
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what does degrees of freedome fix in a data set?
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it corrects for sampling error
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