Outline for Today

1
Outline for Today

• Course evaluations (call 95278 Fraley)
• Announcement of extra-credit class exercise
• Brief Lecture on forecasting
• A comment on the upcoming Exam 4

2
Zodiac exercise

• Go to the following web page (there is a link you
  can click on the syllabus page)
• http//p034.psch.uic.edu/cgi-bin/psych242-zodiac/p
  sych242-process2.pl
• Youll need to follow the directions carefully
  (e.g., dont use the back button in your
  browser window during the exercise).
• Youll need to enter your alias to get credit.
• Try to do this before Thursday. I would like to
  summarize the results and incorporate them into
  the final exam.
• Use the campus computer labs (high-speed). This
  wont work well with a standard phone-line modem.

3
Theoretical Models and Accuracy

• As we discussed previously, one of the most
  useful ways of evaluating a theoretical model is
  to compare the predictions of the model against
  empirical data
• Unfortunately, many industries do not provide you
  with information on the accuracy of their
  predictions
• how many people improve after taking a drug
• how many people actually lose weight by eating
  Subway sandwiches
• how many horoscopes accurately predict the future
• As a consequence, it is almost impossible for
  you, as a consumer, to evaluate the quality of
  the product

4

• In general, weather forecasters make their
  predictions based on either mathematical
  models/simulations of weather systems, past
  weather conditions, intuitive judgments based on
  the movement of current weather systems, or all
  of the above

5

• Unfortunately, weather forecasters do not tell
  usthe consumershow accurate their forecasts
  are. We dont know what the track record is
  for any weather/news team. (Moreover, they
  dont keep records of past forecasts on their
  websites, thereby preventing consumers from
  investigating the matter themselves.)

6

• Students recorded the 5-day forecasts (on Sunday
  nights) for the following channels
• ABC channel 7 (Jorge Lamas)
• Marcs station (Marc Hallez)
• WGN (Katie Cinquegrani)  
• I recorded the actual, end-of-the-day weather
  from an unrelated source Weather Underground.
• This allows us to compare the predictions made by
  the different teams with the actual weather.

7
Average temperature observed, as recorded by
Weather Underground, Chicago
80
60
Median temperature
40
20
March 25 - 31
April 1 - 20
8
Predictions made by ABC, Channel 7, on Sunday
nights
Date Predicted Observed Discrepancy
3/25 27.0 28.0 1
3/26 31.0 32.0 1
3/27 39.0 35.5 3.5
3/28 46.0 42.0 4
3/29 40.0 42.5 2.5
4/1 44.0 35.5 8.5
4/2 37.0 41.5 4.5
4/3 31.5 35.5 4
4/4 34.0 35.5 1.5
4/5 45.0 37.5 7.5
4/8 47.0 45.5 1.5
4/9 43.0 42.5 1
4/10 51.0 52.0 1
4/11 57.0 63.5 6.5
4/12 59.0 53.0 6.0
Average discrepancy 3.6 degrees, SD 2.6
degrees not bad, eh?
9
Week 1
Week 2
Week 3
8
6
Error
4
2
0
M
T
W
R
F
M
T
W
R
F
M
T
W
R
F
Day
Day
Day
Composite
Errors tended to get larger as more days passed
between when the prediction was made (Sunday
evenings) and the day in question. Even 5 days
later, the forecast was only off by 5 degrees, on
average.
6
5
4
Error
3
2
1
0
M
T
W
R
F
Day
10
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11
Date Observed Predicted
3/25 28.0
3/26 32.0 28.0
3/27 35.5 32.0
3/28 42.0 35.5
3/29 42.5 42.0
4/1 35.5 42.5
4/2 41.5 35.5
4/3 35.5 41.5
4/4 35.5 35.5
4/5 37.5 35.5
4/8 45.5 37.5
4/9 42.5 45.5
4/10 52.0 42.5
4/11 63.5 52.0
4/12 53.0 63.5
As an additional comparison, we can generate
predictions in another way based on day before
temperature In this case, were assuming that
the best bet for tomorrows temperature is
todays.
12
Day-before method
ABCs method
80
80
60
60
Actual temperature
40
40
20
20
20
40
60
80
20
40
60
80
Predicted temperature
Predicted temperature
Average discrepancy 3.6 degrees
Average discrepancy 7.7 degrees
13
Summary

• It appears that both weather teams do a pretty
  good job in predicting the temperature
• They were only off by approximately 3.5 4.6
  degrees, on average.
• Their ability to make accurate forecasts was
  lower for extended forecasts
• Nonetheless, you wouldnt know how good they are
  without doing the research yourself. Are other
  stations better? ABC WGN seem to be fairing
  better than Marcs station.