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PSYC 2101: Exam 1
population
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a complete collection of all the units or elements that are of interest in a statistical study
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sample
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a portion of the population selected to represent the whole population
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parameter
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a numerical quanitity which sumarizes some characteristic of the population
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statistic
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a numerical quantitiy which sumarizes some characteristic of the sample
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variable
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a characteristic of the elements of a population
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descriptive statistic
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a class of methods for describing the characteristics of a set of numbers
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inferential statistics
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a class of methods for making valid inferences about an entire population based on results obtained in a sample
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cumulative frequency
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add up the number of scores occuring in the interval and all lower intervals
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proportion
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frequency / total number of scores in sample
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cumulative proportion
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cumulation frequency / n
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cumulative percentage
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cumulative proportion x 100
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what side is frequency always on?
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the ordinate or y-axis
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negatively skewed
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tail is on left. skewed left. freqency is low for low scores
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positively skewed
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tail is on right. skewed right. frequency is high for low scores.
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sum of squares
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subtract the mean from each score then square that.
add up all the squares.
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variance
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SS/N
sum of squares divided by total number of scores
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standard deviation
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square root of (SS/N)
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what happens when the distribution of scores is symmetric
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the mean and median will be equal
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what happens when the distribution of scores is positively skewed
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the mean will be larger than the median.
the mean will be pulled upward away from teh center by the extremely high scores
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what happens when the distribution of scores is negatively skewed
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the mean will be pulled downward and will be lower than the median
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z-score
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(raw score - mean)/ stand. dev
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z-score characteristics
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1. the mean of a set of z-scores is 0.
2. the stand. dev. of a set of z-scores is 1.
3. the variance of a set of z-scores is 1.
4. the sum of squares of a se of z-scores = n.
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