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/psych242-process2.plhttp://p034.psch.uic.edu/cgi-bin/psych242-zodiac/psych242-process2.pl You’ll need to follow the directions carefully (e.g., don’t use the “back” button in your browser window during the exercise). You’ll 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 won’t 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 us—the consumers—how accurate their forecasts are. We don’t know what the “track record” is for any weather/news team. (Moreover, they don’t 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) –Marc’s 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. Median temperature 20 40 60 80 March 25 - 31April 1 - 20 Average temperature observed, as recorded by Weather Underground, Chicago

8. DatePredictedObservedDiscrepancy 3/2527.028.01 3/2631.032.01 3/2739.035.53.5 3/2846.042.04 3/2940.042.52.5 4/144.035.58.5 4/237.041.54.5 4/331.535.54 4/434.035.51.5 4/545.037.57.5 4/847.045.51.5 4/943.042.51 4/1051.052.01 4/1157.063.56.5 4/1259.053.06.0 Average discrepancy: 3.6 degrees, SD 2.6 degrees ~ not bad, eh? ~ Predictions made by ABC, Channel 7, on Sunday nights

9. Day Error 0 2 4 6 8 Day Week 1Week 2Week 3 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. MTWRFMTWRFMTWRF 0 1 2 3 4 5 6 Error Day MTWRF Composite

10. Predicted temperature Actual temperature 20406080 20 40 60 80 Average discrepancy: 3.6 degrees ABC’s method 20406080 20 40 60 80 Predicted temperature Average discrepancy: 4.6 degrees Marc’s station 20304050607080 20 30 40 50 60 70 80 Predicted temperature Average discrepancy: 3.5 degrees WGN’s method

11. DateObservedPredicted 3/2528.0 3/2632.028.0 3/2735.532.0 3/2842.035.5 3/2942.542.0 4/135.542.5 4/241.535.5 4/335.541.5 4/435.5 4/537.535.5 4/845.537.5 4/942.545.5 4/1052.042.5 4/1163.552.0 4/1253.063.5 As an additional comparison, we can generate predictions in another way: based on “day before” temperature In this case, we’re assuming that the best bet for tomorrow’s temperature is today’s.

12. Predicted temperature Actual temperature 20406080 20 40 60 80 20406080 20 40 60 80 Average discrepancy: 3.6 degrees Predicted temperature Day-before methodABC’s method 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 wouldn’t know how good they are without doing the research yourself. Are other stations better? ABC & WGN seem to be fairing better than Marc’s station.