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 USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam

#1
07-31-2011
 USMLE Forums Guru Steps History: Not yet Posts: 404 Threads: 108 Thanked 71 Times in 48 Posts Reputation: 80
Biostats

hey !

can someone explain this to me written on pg-55 FA 2011....

"if the 95% confidence interval for a mean difference between 2 variables includes 0 ,then there is no significant difference and null hypothesis is not rejected.."

anyone out there than can explain this to me!

#2
07-31-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,268 Times in 881 Posts Reputation: 3278

Imagine this scenario:

H0: A new treatment is not more effective than the traditional one
HA: A new treatment is more effective than the traditional one

The 4 options are:

1. Adopt the new treatment when in reality the new treatment is more effective = Correctly rejecting the null hypothesis - Power
2. Continue with the traditional treatment when in reality the new one is more effective = Type II Error - the event that the null is not rejected when the alternative is true
3. Continue with the traditional treatment when in reality the new one is not more effective = Correctly not rejecting the null hypothesis
4. Adopt the new treatment when in reality the new one is not more effective = Type I Error - the event that the null hypothesis is rejected when H0 is actually true

Now, in statistics, the test statistics is always under the null (H0):
1.- When we are talking about the difference in proportions between group A & B OR the difference in means between group A & B, our test statistic follows H0 = where the null value equals zero
2.- When we are comparing Odds Ratio/Risk Ratio, again our test statistic follows H0, but this time the null value would be equal to one (OR or RR = 1 under the null).

When we have 2 groups and we calculate a 95% CI for the diff. in means between groups

[-10,10] = the null value (null value = 0) is included in the CI = you fail to reject H0 (no difference)
[0.001, 10] = the null value (null value = 0) is not included in the CI = you reject H0

For more check here:
The Zero value in Confidence interval?
 The above post was thanked by: alice (10-16-2012), heman466s (07-31-2011)
#3
07-31-2011
 USMLE Forums Guru Steps History: Not yet Posts: 404 Threads: 108 Thanked 71 Times in 48 Posts Reputation: 80

Quote:
 Originally Posted by bebix Imagine this scenario: H0: A new treatment is not more effective than the traditional one HA: A new treatment is more effective than the traditional one The 4 options are: 1. Adopt the new treatment when in reality the new treatment is more effective = Correctly rejecting the null hypothesis - Power 2. Continue with the traditional treatment when in reality the new one is more effective = Type II Error - the event that the null is not rejected when the alternative is true 3. Continue with the traditional treatment when in reality the new one is not more effective = Correctly not rejecting the null hypothesis 4. Adopt the new treatment when in reality the new one is not more effective = Type I Error - the event that the null hypothesis is rejected when H0 is actually true Now, in statistics, the test statistics is always under the null (H0): 1.- When we are talking about the difference in proportions between group A & B OR the difference in means between group A & B, our test statistic follows H0 = where the null value equals zero 2.- When we are comparing Odds Ratio/Risk Ratio, again our test statistic follows H0, but this time the null value would be equal to one (OR or RR = 1 under the null). When we have 2 groups and we calculate a 95% CI for the diff. in means between groups [-10,10] = the null value (null value = 0) is included in the CI = you fail to reject H0 (no difference) [0.001, 10] = the null value (null value = 0) is not included in the CI = you reject H0 For more check here: The Zero value in Confidence interval?

#4
07-31-2011
 USMLE Forums Master Steps History: 1+CK+CS+3 Posts: 1,357 Threads: 194 Thanked 3,268 Times in 881 Posts Reputation: 3278

Quote:
hahahaha....

Message:
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