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34 Cards in this Set
- Front
- Back
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Average
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A list of numbers equals their sum, divided by how many there are
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Cross sectional study
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different subjects are compared to eachother at one point in time
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Longitudinal study
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subjects are followed over time, and compared with themselves at different points in time
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A histogram balances when supported at the _________
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Average
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Median
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the value with half the area to the left and half the area to the right
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The median of a list is defined so that _____ or more of the entries are at the median or ______ and half or more at the median or _______
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half; bigger; smaller
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Steps of the root mean square
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-square all the entries
-take the average of the squares -take the square root of the mean sqrt [average of (entries^2)] |
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Standard Deviation
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says how far aways numbers on a list are from their average
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Roughly ___ % of the entries on a list are within one SD of the average
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68
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Roughly ___ % are within two SDs of the average
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95
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deviation from average =
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entry-average
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Steps to find the SD
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-Find the average
-Find the deviations from the average -find the r.m.s. of the deviations |
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Alternative way to find SD
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sqrt [ (average of (entries^2)) - (average of entries)^2 ]
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______ locates the center of a histogram
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Average
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r.m.s. measures how ____ the entries are, neglecting signs
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big
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The normal cure is always ____ the horizontal axis
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above
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Area under the normal curve between -1 and +1 is about ___ %
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68
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Area under the normal curve between -2 and +2 is about ___ %
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95
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Area under the normal curve between -3 and +3 is about ___ %
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99.7
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A value is converted to ________ ______ by seeing how many SDs it is above or below the average
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standard units
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How to estimate the percentage of entries in an interval (normal approximation)
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-convert the interval to standard units
-find the corresponding area under the normal curve |
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Interquartile range =
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75th percentile - 25th percentile
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Percentile
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score
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Percentile rank
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percent
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z=
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score - average
__________________ SD |
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Adding the same number to every entry on a list adds that constant to the average; the SD ______ change
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does not
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Multiplying every entry on a list by the same positive number ________ the average and the SD by that constant
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multiplies
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Standard units say how many _____ a value is, above(+) or below(-) the average
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SDs
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If a measurement is repeated it will probably come out a bit differently. By how much? The best way to find out is to _________ ____ ______________
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replicate the measurement
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The ____ of a series of repeated measurements estimates the likely size of the chance error in a single measurement
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SD
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individual measurement =
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exact value + chance error
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Affects all measurements the same way, pushing them in the same direction
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Bias
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Change from measurement to measurement, sometimes up and sometimes down
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Chance errors
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when bias and chance error are present,
individual measurement = |
exact value + bias + chance error
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