Sample NMS Reference Report by YONTCHANG G - University of ...

4. Text boxes showing the chance (proportion) of experiencing floods and crop failure
during the month of August:
Simple Models - Normal Distribution, One Sample
TINt 'Flooding'
Normal model, one sample
Column Flooding
Sample size 57
Minimum 0
Maximum 308
Range 308
Mean 214
Std. deviation 76.272
Standard error of mean = 10.103 with 56 d.f.
95% confidence interval for mean 193.76 to 234.24
From our sample of 57 years, the true mean date of the start of threatening flooding ( from
1 st August, 100mm or more of rain/ 1day) is estimated to be day 214(1.August) and is highly
likely to be between day 193 (11.July) and day 234 (21.August). I am 95% confident that the
margin error is ± 20 days (about 3 weeks).
WEEK 1 CHANCE OF CROP FAILURE
One proportion - binomial model
BINomial;stats 57 12;SIMple;EXAct
Binomial model, single sample
Sample size 57
Successes 12
Proportion 0.211
Approx s.e. of proportion = 0.054
Exact results:
95% confidence interval for prop. 0.114 to 0.339
Simple normal approximation:
95% confidence interval for prop. 0.105 to 0.316
The 95% confidence interval for the true risk of flooding with crop failure for the first week in
August is from 11.4% to 33.9%.
Estimated value (proportion) = 0.211 (21.1%)
s.e. = 0.054 (5.4%)
The risk of crop failure during week 1 of August is (12/57): 21.05% or about 21% with a
return period of (1/0.2105 = 4.75) about 5 years. I am 95% confident that the estimate of
21.1% is within ± 11.25% of the true risk of flooding with crop failure for the first week..
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