Eyedocs statistics

Question 1

What is the power of a study?

Answer 1

The probability of not producing a type II error, or the probability of rejecting the a false null hypothesis

Question 2

What are the factors that affect the power of a study (4)

Answer 2

1. Sample size (> size, > power)
2. Significance level (> alpha, > power)
3. Population variance (< variance, > power)
4. Size of difference, (> difference, > power)

Question 3

What is the equation for variance, and the co-efficient of variation?

Answer 3

1. standard deviation squared
2. standard deviation / mean.

Question 4

What is the formula for number needed to treat?

Answer 4

the reciprocal of the difference of the proportion of the two positive outcomes

Question 5

What is McNemar’s test?

Answer 5

McNemar’s test is used to compare two proportions in paired groups. It tests the null hypothesis that the proportions of individuals with a given characteristic are equal in two related groups in the population. McNemar’s test statistic follows the Chi-squared distribution on one degree of freedom.

Question 6

What is the calculation of relative risk? What is the calculation of absolute risk?

Answer 6

absolute risk
number of cases of disease in exposed /
number of individuals exposed

relative risk
disease incidence in exposed /
disease incidence in non-exposed

Question 7

What is the definition of attributable risk?

Answer 7

Disease incidence in exposed - disease incidence in non exposed

Question 8

What is the odds ratio?

Answer 8

odds of subject with disease exposed to risk factor /
odds of subject without disease exposed to risk factor

Question 9

What is the difference between type I and type II error?

Answer 9

Type I error - false positive (falsly rejecting null hypothesis

Type II error - false negative (falsly agreeing with the null hypothesis)