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BBS1003-Statistics-Syllabus summary, lectures, videos, Andy Field

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This summary scored me a 9.7 on the final exam! This document contains a summary of the statistics syllabus, notes from the lectures, notes on the video lectures and a summary of parts of Andy Field's statistics book.

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  • February 5, 2019
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  • 2018/2019
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Summary statsttis syllabus

Chapter 1
Variables
Various types:
 Qualitative  nominal and ordinal
o Also called categorical or discrete
 Quantitative  interval and ratio
o Also called continuous  variable can take any number

Frequentiy table
 To summarize e.g. scores of students
 Vertically  columns
 Horizontally  rows

Bar tihart
 Graph with frequency/count on vertical aais and scores on horizontal aais
 Blank between each bar  the bar can be assigned to e.g. any political party, so
there is a blank between each pair of bars and the distance between the bars has no
meaning
 Often used to summarize outcome of qualitatve variable

Histogram
 For summarizing quantitative variables
 No space between bars  scores are connecting as it should for interval and ratio
variables
o Each bar has surface eaactly equal to frequency of score represented by that
bar
 To ensure this for a bar width other than 1, the numbers on the y-aais
have to be divided by the class width
o Horizontal end points of each bar are chosen by user  determine width
 For very large sample sized, percentages can be presented instead of frequencies
Boundaries
 [..,..)
o [ = included in class interval
o ) = not included in class interval

Theoretti distributon
 When number of classes becomes very large 
obtain theoretic distribution

,Measures of tientral tendentiy
 Mode
o Score with highest
frequency
 Median
o Middle value
 Mean
o Average
Skewness
 Right skewed (+) 
average is the highest
because most sensitive to
eatreme values  right skew means there are more large values

Variantie
 How much subjects difer from each other with regard to their scores
 You can calculate how much measurements difer from the mean  but then -2 and
+2 would cancel each other out  you can solve this by calculating the average sum
of the quadratic diference of all values around the average  variantie




 8 = number of measurements



 If you do not divide by N (8 in this case)  statistic is called variation
o So variation = N a var(Xn)
 Population vs sample:
o Population  divide by N-1
o Sample  divide by N

Standard deviaton
 Square root of variance
 More usable  eapressed in same scale as value (so e.g. inches)
o Variance is not  square of value, so e.g. square of inches


Normal distributon
 Theoretic distribution
 Features:
o Symmetric  so average, mode and median will coincide

, o 68% of scores falls within 1 standard deviation
of average
 95% will fall within 2 standard deviations
 99.7% will fall within 3 standard deviations

Pearson tiorrelaton
Standardization
 Covariance needs to be converted to standard set of units to avoid dependency on
measurement scale  standardizaton
o Standard deviation typically used as unit
 By dividing the distance from the mean by the standard deviation, you
get the distance in standard deviations
 Standardized covariance is known as tiorrelaton tioeftiientt




o Sa is standard deviation of frst variable, Sy is of second variable
o Coefficient is known as Pearson product-moment correlation coefficient
o Can only be between -1 and +1
 -1 = perfectly negative correlation  values go in same direction
 +1 = perfectly positive correlation  values go in opposite direction
 Other formula for Pearson tiorrelatont







Chapter 2
Linear regression
 Determining the approaimately average Y value for a given Xn value
 When dependent variable is quantitative
Diference correlation and regression:
 Correlation is symmetric
o If Xn is correlated to Y, then Y is also correlated to Xn by the same amount
 Regression is asymmetric
o Determining average Y for given Xn is diferent than determining average Xn for
given Y
Independent and dependent variables
 Independent  variable is a cause, value does not depend on another variable
 Dependent  value of variable depends on cause
Designs
 Longitudinal  subject measured repeatedly

,  Cross-sectional  only measured once  no repeated measurements



Regression line
 Summarizes scatter plot by a straight line
 Straight line that minimizes sum of all squared
deviations of observations from regression line
 Useful for calculating e.g. predicted length for age
value
Residuals:
 Deviations of observation from the regression line
Equaton


Deviaton of predicted value from observed Y^ value of
child



Least squares method
 Straight line that minimizes sum of all squared deviations of observations from that
line minimizes sum of squared residuals
 Regression slope:

o
 Regression intercept


o

R-square
 Measure of how good data can be summarized by regression line
 Range is between 0 and 1
o R=1  all of total variation is eaplained by regression line
Total variaton to be explained/total variaton
 Variation


 Denoted as SS(Y) or SS(total)
 Fraction of total variation eaplained by regression line  R-square
Unexplained variaton


 Denoted as SS(residual) or SS(uneaplained)

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