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Exam 2 Statistics
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Statistics for Psychology Exam 2
Terms in this set (26)
Critical Properties for Normal Distribution
1. Symmetrical
2. Unimodal
3. Mean = Mode = Median
4. Has a bell shape
5. Curve never touches x-axis
Standard Score
Score is expressed in terms of some standardized unit measurement
Z-Score
Raw score expressed in standard deviation units. Represents how many standard deviations a single score is from the mean.
Probability
relative frequency of a particular outcome occurring over an infinite number of trials or occasions.
- expressed as proportion, which varies between .00 and 1.0
Probability of .00
Outcome will NOT occur
Probability of 1.0
Outcome will DEFINITELY occur
Independent outcome
the outcome of one trial has no relationship to the outcome of another trial.
Whenever you have independent outcomes, then you can multiply the probabilities of the individual outcomes to find the probability that these outcomes will occur together.
Descriptive Statistics
procedures for summarizing a group of scores
Inferential statistics
statistics used
Sampling
process of drawing a sample
Representative sample
sample whose relevant characteristics are similar to those of the population
Simple random sample
ever case in the population has an equal chance of being selected
Convenience sampling
researcher uses whatever subjects are available (bad!)
Random assignment
an experimental technique for assigning subjects to different treatments (or no treatment)
Independent variable
the treatment condition that the researcher expects will make subjects perform either better or worse on some measure of behavior
Dependent variable
measured behavior (which the researcher assumes is attributed to the treatment)
Extraneous or Confounding variables
unintended variable that coexists with the independent variable and may explain the measured effect in the dependent variable
Directional research hypotheses
states that the independent variable is expected to result in the better (or worse) effect on the dependent variable
Nondirectional research hypotheses
states that the independent variable is expected to have an effect on the dependent variable but it does not specify how
Sampling error
deviation from expectation that is due to mere chance
Significant difference
any difference that is greater than would be expected by mere chance
Sampling Distribution of the Mean
The distribution of means of an infinite number of samples of a given size from a population
Key Properties of Sampling Distribution that are critical to inferential statistics
1. Mean of the sampling distribution
2. Standard deviation of the sampling distribution
Shape of the sampling distribution
Mean of the Sampling Distribution
"Mean of the Means" (Mm)
Central Limit Theorem
The shape of the sampling distribution of the mean will approximate a normal curve if the sample size is sufficiently large (let's us determine if something is a common or rare event)
Interval Estimate
predicted range of values in which the true population mean probably falls
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