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1. If of a sample of 400 people, the mean for X is 200 and the standard deviation is 10, the 95%
confidence for the mean is_200±0.98___________
2. If of a sample of 900 people the mean is 180 and the standard deviation is 15, the 95%
confidence for the mean is__180±0.98__________
3. Would you say there is a difference between the two populations represented by the above two
means? Explain: Yes. 95% CI for mean do not overlap
4. The number of women with breast cancer in a small town in Croatia where 90, n=4000, and on
an island 180, n=950. Would you say there is a difference between these populations? Explain.
95% CI for proportion in small town was 0.0225±0.0046 whereas 95% CI for proportion on
island was 0.1895±0.0249. The 95% CI do not overlap so there is statistically significant
difference between these populations.
5. The ministry has chosen a random sample of 2000 people from the phonebook list of 100,000.
People were asked if they still support the president. 44 percent of the sample said yes. What is
95% confidence interval for those still supporting the president?
Sample size is 2000, so 95% CI is 0.44±0.02.
6. 350 patients were allocated to standardized to zone diet and 182 to Atkins diet. At 24 months
months, the first group showed a mean loss of 2.1 kg (95% CI 0.70 to 3.52) and the second 1 kg
(0.5 to 2). Which diet would you recommend?
Mean loss with zone diet is 2.1 kg (95% CI 0.70 to 3.52). We can be 95% confident that these
people lost on average from 0.7kg to 3.52 kg so the diet is effective (does not include 0).
Mean loss with Atkins diet is 1 kg (0.5 to 2). This implies that we are 95% confident that these
people lost on average from 0.5 to 2 kg and the diet is also effective (does not include 0).
So both diets are effective. Comparison of 95% CI between two groups indicated CIs ovelap
(from 0.7 to 2 kg) so diets are also comparable and we could recommend either (there is no
evidence that one diet is more effective than other).
7. If a 95% confidence interval for a curing fewer with a new experimental drug X01PR is from
-1 % to 25%, would you recommend the drug?
95% CI for proportion is from -1% (the drug actually increases the frequency of cases) to 25%
(the drug actually decreases the frequency by 25%) compared to control (best available
treatment). The CI includes 0 (no effect) so you will not recommend the drug.
8. In a town there are 80 000 people. Half of them drink green tea and half
drink black tea. Suppose 250 people were found to suffer from migraines in the first group, and
490 in the second group. What is the NNT to prevent migraine by drinking green tea?
Improvement rate in experimental group (green tea)=(40000-250)/40000=0.99375
Improvement rate in control group (black tea)=(40000-490)/40000= 0.98775
AAR=0.99375-0.98775=0.006
NNT=1/ARR=1/0.006=166.67~167 people
9. Treatment of severe poison ivy: a randomized, controlled trial
BACKGROUND: Toxidendron (poison ivy, oak, and sumac) contact dermatitis is a common
complaint in the outpatient primary care setting with little evidence-based guidance on best
treatment duration.
METHODS: This randomized, controlled trial examined the efficacy and side effects of a 5-day
regimen of 40 mg oral prednisone daily (short course) compared to the same 5-day regimen
followed by a prednisone taper of 30 mg daily for 2 days, 20 mg daily for 2 days, 10 mg daily for
2 days, and 5 mg daily for 4 days over a total of 15 days (long course) in patients with severe
poison ivy dermatitis.
RESULTS: In 49 patients with severe poison ivy, non-adherence rates, rash return, medication
side effects, and time to improvement and complete healing of the rash were not significantly
different between the two groups. Patients receiving the long course regimen utilize other
medications in 22.7% vs. 55.6% those on short regiment, P = 0.02, number needed to treat 3.05.
Which treatment would you recommend and why? – We will evaluate your way of thinking here.
It is not necessary for your answer to be identical to the given solution.
The abstract is inconclusive. Authors state that treatments are comparable in terms of nonadherence rates, rash return, medication side effects, and time to improvement and complete
healing of the rash meaning that as long as these variables are considered we could use either
treatment. The observation on decreased usage of second medication in “long course” vs “short
course” is not considered valid evidence as we do not have information whether this was a fair
comparison (ie. usage of other medications measured after “long course” treatment ended at ie 16
th day).