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37 Cards in this Set
- Front
- Back
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Measures of Central Tendency
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Mean, Median & Mode
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Central Tendency
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A measure that identifies a single score as representative for an entire distribution
(Relative position) |
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Mode
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- Most repeated/frequent score in the set of results
- Best for nominal data |
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Median
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- The score that divides the distribution in half
- Best for ordinal data |
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Mean
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- The arithmetic average
- Best for interval/ratio data |
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Measures of Dispersion
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A single summary figure that describes the spread of observations within a distribution
(Amount of variation) |
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Variation Ratio (VR)
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= 1 - % of cases in the mode
- paired with the mode - ranges from 0 (no variation) to 1 - used for nominal variables |
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Range
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= X(largest) - X(smallest)
- used for interval/ratio variables - insensitive measure of dispersion - NEVER best measurement |
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Inter-Quartile Range (IQR)
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= Range of scores representing the middle 50% of the distribution
- used for interval/ratio variables - paired with the median |
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Standard Deviation (SD)
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= Describes the "average" distance of the values from their mean
- paired with mean |
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Variable
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A characteristic of person, place or thing, that can assume more than one value (i.e. letters in the alphabet)
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Constant
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Can only assume one value (i.e. inches in a ft)
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Discrete
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Whole numbers (i.e. placement in a race)
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Continuous
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Can hold any value (i.e. times you can finish a race)
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Independent Variable
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One that is controlled or manipulated by the researcher
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Dependent Variable
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One that is affected by the independent variable (outcome variable)
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Measurement
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The process of assigning number to variable of interest according to specified rules or conventions
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Levels of Measurement
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1) Nominal
2) Ordinal 3) Interval 4) Ratio |
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Nominal
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Attributes are only named
(i.e. large, medium, small) - does not have any characteristics of measurement |
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Characteristics of Measurement
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1) Magnitude (more or less)
2) Interval (equal distance) 3) Ratio (does it have a zero) |
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Ordinal
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Attributed can be ordered
(i.e. letter grade) - magnitude only |
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Interval
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Distance is meaningful
(i.e. course evaluations) - magnitude & intervals - open ended response (45+ yrs) |
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Ratio
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Absolute zero
(i.e. height) - magnitude, intervals & ratio |
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Why do you need to know the level of measurement?
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So you know what tests to run
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Can a variable possess more than one level of measurement?
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YES
- i.e. blood pressure if categorized to normal, prehypertension and high (ordinal because high is 140+) |
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Sample
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Cohort used to generalize results to population
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Population
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Everyone you are interested in studying
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Normal Distribution
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- Bell-shaped
- Unimodal (one mode) - Symmetrical - Asymptotic - Mean=Median=Mode |
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The larger the sample size...
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The closer to normal distribution...
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Positively Skewed
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- Bulk of scores are on the left
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Negatively Skewed
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- Bulk of scores are on the right
- i.e. Mean=82, Median=80 and Mode=75 |
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Kurtosis
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1) Leptokurtic distribution (leap-up)
2) Platykurtic distribution (flat/smooth) |
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Print out for Kurtosis
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Negative value = Platykurtic
Positive value = Leptokurtic Severely if +/- 2.00 |
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Print out for Skewness
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Negative value = Negatively skewed
Positive value = Positively skewed Severely if +/- 3.00 |
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Area under a normal distribution
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68% within 1 SD
95% within 2 SD 99.7% within 3 SD |
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How to calculate # of SD from the mean
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+/- 1 SD = Mean +/- 1*SD
+/- 2 SD = Mean +/- 1.96*SD +/- 3 SD = Mean +/- 2.58*SD |
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Z-Scores
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Identify and describe the exact location of every score in a distribution
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