Introduction



1. Need for statistics

















i. population -> parameters







ii. Sample -> statistics









2. Variables

3. Notation



X, Y



N



Xi



X1





4. Measurement Scales









5. Limits of Measurement



















Frequency Distributions



1. Frequency Distributions--Question answered: How many people got this score





100.00 1

99.00 2

95.00 2

90.00 2

87.00 1

83.00 1

77.00 1

75.00 1

74.00 1

70.00 3

67.00 2

66.00 5

64.00 2

55.00 2

50.00 3

43.00 1



3. Percentiles--Question answered: What score does a certain percentage of people fall below? (Or what's the cutoff point?)



Percentile Value
25 64.286
50 68.2
90 97


3. Graphing Frequency Distributions

A. Basic Rules

1. Scores go on X, Frequencies on Y

2. Both axes start of at O; if not break the axis

3. Y about 3/4 of X (see p. 50)

4. Label each axis







B. Bar graph of nominal, ordinal data

1. Bars don't touch

2. Height is frequency

CATEGORY OF WORKER WEEKLY EARNINGS ($)
Professional, tech. 277
Managers 302
Sales workers 225
Clerical workers 167
Craftspeople 259


C. Histogram

1. Interval/ratio data

2. Bars for each interval from lower to upper limit

3. Bars touch (continuous variables)

4. Midpoint is marked on X axis







D. Frequency Polygon

1. Interval/ratio data

2. Like histogram except midpoints are plotted and joined with straight lines

3. Close off with interval above and below to zero (gives impression of the "shape" of the distribution)







E. Shapes of Frequency distributions--tell us about data

1. Symmetrical: if when folded in half the two sides coincide

e.g., bell shaped/normal curve





2. Skewed: if not symmetrical

a. positive=tail at the positive end

b. negative=tail at the negative end