PSYCH 210: Exam #1
68 Cards in this Set
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A characteristic or condition that varies and has different values in different people or at different times
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Variable
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Measuring variables
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data
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Scales of Measurement
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NOIR
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to classify
-Diagnosis, Genotype, Dead/Alive etc.
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Nominal (Qualitative)
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Order-unequal intervals
-social rank, race finish, birth order, intervals can be different
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Ordinal (Qualitative)
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Distance, magnitude
-equal intervals, arbitrary "0", temperature (C,F), opinion
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Interval (Quantitative)
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Origin
-Natural "0", temperature in K, brain volume, # of convictions, time
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Ratio (Quantitative)
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Describes data
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Descriptive statistics
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Lets us infer using samples to study populations, uses probability
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Inferential statistics
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Help us understand populations
-represents population in a study
-has "n" individuals
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Sample
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The entire set/group of individuals you could potentially observe
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Population
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characteristics of populations
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Parameters
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characteristics of samples
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Statistics
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(Hopefully small) discrepancies that almost always occur
-Larger sample should have smaller sampling error from populations values
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Sampling error
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Links samples and populations
-replication is important
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Probability
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What measurement scale? Inches
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Ratio
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What measurement scale? Weather conditions
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Nominal
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What measurement scale? Rank order of favorite NCAA teams
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Ordinal
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What measurement scale? Weight in pounds
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Ratio
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What measurement scale? Religious affiliation
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Nominal
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What measurement scale? Distance
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Interval
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An equal chance for inclusion in sample
-each set of members is equally likely
-discrepancy of M from Mu is random
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Random Selection
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Sample where demographics are in proportion (Good)
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Stratified random sample
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Sample of only Intro Psych students (randomly selected)
(Not as good)
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Convenience sample
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Least useful sample, be cautious (Bad)
-biased
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Self-selected sample
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-Pre-existing patterns
-preexisting groups compared (difference in mean?)
-don't know if causal or not
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Correlation
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-Artificially create groups that differ on a variable
-record differences in another variable
-what's the advantage? Causation
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Experiment
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Measure naturally occurring associations
-quantify pattern in 2 observed random variables (x,y)
-compares means
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Nonexperimental, Correlational Studies
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Finding cause
1) Manipulation of Independent variable
2) Control of confounding variables
3) Observe dependent variable
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Experimental Study
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A factor manipulated by the experimenter. The focus of the study.
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Independent variable
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Factor that may change in response to an independent variable. Can be multiple
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Dependent variable
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3 Preventing confounds practices
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1) Random assignment - to treatment/control condition
2) Holding constant - same treatment for everyone (e.g. all surgeons right handed)
3) Matching (participants) e.g. anxiety level, R/L handed
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Internal attributes or characteristics that can't be directly observed but are useful for explaining/describing behavior
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Constructs
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Identifies an observable variable theoretically related to a construct
-defines the construct in terms of those measurements
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Operational Definitions
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Typically whole, countable numbers with no intermediate values possible
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Discrete variables
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Free to choose precision, indefinitely divisible categories
-real limits=-1/2 unit, +1/2 unit
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Continuous variables
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Shows the number of individuals (f) in each category (x) on a scale of measurement
-organizes and reveals trends
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Frequency Distribution
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"Intervals" of X values
-summarize, condense measurement categories
-lose precise frequencies
-O/I/R scales
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Grouped Frequency Distributions
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Unequal intervals that don't touch
-Nominal, Ordinal
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Bar Graph
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Quantitative scale, extends to real limits
-Ratio, Interval
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Histogram
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Has to start and end at bottom (0)
-Ratio, Interval
-rarely used, except published research
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Polygon
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Positive skew: Too hard
Negative skew: Too easy
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Floor Effect
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Higher percentiles always equal higher _______
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scores
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The sum of the scores divided by the number of scores
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Mean
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Distance from the Mean
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Deviation score
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The sum of the Deviation scores =
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0
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M=20
-add 1 to every score what is the new mean?
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21
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(SumX1 + SumX2) / (n1 + n2)
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Weighted Mean
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Mean is not appropriate for _____ & _______ scales
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Nominal, Ordinal
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Cares more about rank order than number values
-midpoint in ordered list of scores
-value dividing distribution in half
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Median
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Most frequent category or score
-always the peak in distribution
-always actual, observed value
-can have multiple
-N,O,I,R
-highest frequency
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Mode
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Positive skew: left to right (M,Mdn,Mo)?
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Mean, Median, Mode
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Negative skew: left to right (M,Mdn,Mo)?
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Mode, Median, Mean
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For a negatively skewed distribution with a Mode of X=25 and a mean of M=20, the Median is probably?
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Between 20 and 25
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Describes a central point of the distribution
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Central Tendency
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How scattered/spread out the scores are
-used to describe/summarize
-used as a basis for most inferential stats
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Variability
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Low variability =
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Better representation of sample
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High variability =
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Unrepresentative sample common
-harder to detect relationships
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Max distance between scores
Continuous: Xmax - Xmin
Discrete: Xmax - Xmin +1
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Range
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Distance covered by middle 50% of the distribution
-useful with vary skewed distribution
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Interquartile Range
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The average distance between a score and the mean
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Standard Deviation
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Average squared distance from the mean
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Variance
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The square root of variance
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Standard deviation
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Sum of Squares (SS)
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SS=Sum(X-M)^2
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Convey each score's distance from the mean in standard deviation units
-rarely used in applied settings (decimals, negative numbers are confusing)
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Z-Score
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Body-percentile rank
Tail-proportion higher than the score
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Positive Z-Score
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Body-proportion higher than the score
Tail-percentile rank
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Negative Z-Score
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p + q=
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1
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PSYCH 210: 225 Ex.1