Practice Exam One
Proponents of the Global warming hypothesis claim that the temperature of the earth is rising and
weather is becoming more volatile. Compare and contrast as completely as possible the
following set of sample data for 1990s weather to 1890s weather when the average daily high
temperature in the United States was 63 degrees with a standard deviation of 25 degrees. The
median temperature in the 1890s was 60 degrees. The following data is a random sample of
1990's daily high temperatures that accurately represents 1990's weather in the United States.
Evaluate the global warming hypothesis in light of this evidence. Are we more likely to see
really hot days now? What about really cold days?
I. Daily high temperatures for randomly selected places and times in the 1990s:
Place/Date
Temperature
San Diego 9/3/93
71
Chicago 1/3/97
15
Phoenix 6/3/92
110
Memphis 3/3/98
68
Philadelphia 8/3/94
86
1990
Mean = 70
Median= 71
Standard deviation = 35
Z100 = (100-70)/35 = .86
Z20 = (20-70)/35 = -1.43
1890
Mean =63
Median = 60
Standard Deviation = 25
Z100 = (100-63)/25 = 1.48
Z20 = (20-63)/25 = -1.72
I arbitrarily chose 100 as “hot” and 20 as “cold”
According to the statistics the weather is warmer now (comparing averages) and more volatile
(comparing standard deviation.) Both hot and cold days are more likely now (lower zs).
Additionally, in 1890 the temperature was positively skewed (a large group of days on the cool
side with a few really warm days, and now it is negatively skewed (a large group of days on the
warm side with a few really cosd days)
Here’s a sketch
1890
13
60 63
113
1990
0
70 71
140
Global warming hypothesis supported!