1. Newsroom Math and Statistics

2. Percentage change (NEW/OLD – 1) Comparing new values to old values
Or: (new – old)/old
€8 million this year, €5 million last year
(8/5 – 1) = 1.6 – 1 = 0.6 = 60%,
So the budget has increased 60%
€5 million this year, €8 million last year
(5/8 – 1) = – 1 = = -37.5%
So the budget has decreased 37.5%

3. Rates
Number of events per some standard unit (per capita, per 100,000, etc.)
Crime rates, accident rates, etc.
RATE = (EVENTS / POPULATION ) * (“PER” Unit)
Use to compare places of different size
Make “per unit” large enough so that the smallest events/population result is >1

4. Consumer Price Index Price Then CPI Then Used to correct for inflation
Get the CPI at
Price Now = CPI Now
Price Then CPI Then

5. Estimating crowds
Beware the “official” estimate from organizers or opponents
Better method:
Estimate the area in sq meters (L x W)
1 person/meter in a loose crowd
Divide by 0,75 for a tighter crowd
Account for turnover?

6. Sample surveys
Random sampling: Everyone has the same chance to be picked
Margin of sampling error:
Error can be caused by
other factors
Avoid unscientific samples such as convenience or phone-in

7. Summarizing data sets Three useful measures
Center: Mean, median, mode
Variability: Maximum/minimum, range, n-tiles, standard deviation
Shape: Standard (bell) curve, skewed…use histogram or stemplot to view
Empirical Rule for bell curve data:
66% of values within 1 StDev of the mean
95% of values within 2 StDevs of the mean
99.7% of values within 3 StDevs of the mean
Look for outliers!

8. Relationships between measurement variables
Correlation: Measures the strength (linearity) of the relationship of two variables
Pearson’s r
Ranges from -1 to 1
-1 and 1 are perfectly strong
0 means no relationship
Positive: Both variables rise together
Negative: One goes down as the other goes up
REMEMBER: CORRELATION DOESN’T NECESSARILY MEAN CAUSATION

9. Linear regression
Equation of the line on an x-y scatterplot that falls closest to all the points
Computer will tell you the slope and intercept
R measures how close the points are to the line
R2 measures “percent of variance explained” by the independent variable
Use to predict a dependent
value based on independent
value.

10. Using Excel

11. What is “data”? Information in table form Columns are the variables
Name, date, time, address, age, etc.
Rows are the records
Persons, incidents, etc.

12. What Excel can do Import data from many formats
Sort data by one or more variables
Filter data to show only selected rows
Transform data using functions and formulas
Summarize data into categories

13. Importing data Common formats Data Import Wizard will help
*.xls (or *.xlsx)
Fixed-width text
Delimited text (comma, tab, etc)
*.dbf files (old dBase)
HTML tables
Data Import Wizard will help