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Chapter 2 (Sections 2.1 and 2.2)
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Gravity
Terms in this set (15)
Percentile
the value with p percent of the observations less than it.
Cumulative Relative Frequency Graph
A cumulative relative frequency graph of a quantitative variable is a curve graphically showing the cumulative relative frequency distribution.
Standardized Value (Z-score)
If x is an observation from a distribution that has a known mean and standard deviation, the standardized value of x is z = x - mean/Standard Deviation. The standardized value is called a z-score. **Observations are often standardized so they can be expressed on a common scale.
Effect of Adding or Subtracting a Constant
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Effect of Multiplying (or Dividing) by a Constant
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Density Curve
a curve that: a) is always on or above the horizontal axis, and b) has an area of exactly 1 underneath it. A density curve describes the overall pattern of the distribution.
Median of a Density Curve
the "equal-areas" point; the point that divides the area under the curve in half.
Mean of a Density Curve
the "balance" point; the point where the curve would balance if it were made of solid material. (use µ (mu) to describe the mean of a density curve) and (use σ for the standard deviation of a density curve.)
Normal Distribution
is described by a Normal Density Curve. Any particular Normal distribution is completely specified by two numbers: its mean, µ, and its standard deviation, σ.
Normal Curve
The mean of a Normal Distribution is at the center of the symmetric Normal Curve. The standard deviation is the distance from the center to the change-of-curvature points on either side.
N(µ,σ)
the abbreviation for the Normal Distribution with mean µ and the standard deviation σ.
The Empirical Rule or the 68-95-99.7 Rule
In the Normal distribution with mean µ and standard deviation σ: a) approximately 68% of the observations fall within σ of the mean µ, b) approximately 95% of the observations fall within 2σ of the mean µ, and c) approximately 99.7% of the observations fall within 3σ of the mean µ.
Standard Normal Distribution
the Normal distribution with mean 0 and a standard deviation of 1.
The Standard Normal table
Table A is a table of areas under the standard Normal curve. The table entry for each value z is the area under the curve to the left of z.
Normal Probability Plot
if points on a Normal probability plot lie close to a straight line, the plot indicates that the data is Normal. Systematic deviations from a straight line indicate a non-Normal distribution. Outliers appear as points that are far away from the overall pattern of the plot.
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