Flashcards in Biostats Deck (14):

1

## What percentage of the populations falls within 1, 2, and 3 standard deviations of the mean of a normal distribution?

###
1 - 68

2 - 95.5

3 - 99.7

2

## What is a positively-skewed distribution?

### One in which the mean is greater than the median, such that the distribution has a longer tail on the right (at greater values)

3

## What is a negatively-skewed distribution?

### One is which the mean is less than the median, such that the distribution has a longer tail on the left (at lower values).

4

## What is the customary alpha-criteria for determining statistical significance?

###
P-values less than 0.05.

In this case, the null hypothesis that there is no difference is rejected, and the alternative is left: that there is a relationship.

5

## What measure can be used to evaluate cohort studies?

###
Relative risk

This is found by dividing the incidence rate of the exposed group by the incidence rate of the control/unexposed group

6

## What is incidence?

### The number of new cases in a given period of time divided by the total susceptible population

7

## What is prevalence?

### The total number of cases in a slice in time divided by the total population

8

## What is the crude mortality rate?

### The number of deaths from all causes divided by the total population

9

## What is the rate of increase of a disease?

### The number of new cases of a disease minus the number of deaths (or cures) from the disease, divided by the total population.

10

## How are incidence and prevalence related?

### Prevalence = incidence * duration

11

## How do you calculate a 95% confidence interval?

###
CI = sample mean +/- Z*(SD/n^-2)

the confidence interval reflects the probability that the confidence interval will contain the true parameter.

12

## What is the difference between a confidence interval and "crude"/"simple" standard of deviation?

### The (95%) confidence interval is an inferential statistic that can be used to decide where the true mean might be, whereas the standard deviation is a descriptive statistic, and cannot be used to make any assumptions about the true mean

13

## What is the relationship between a test's sensitivity and specificity, and the positive and negative predictive values?

### Tests with 100% sensitivity (no false negatives) will have a negative predictive value (NPV) of 100%; tests with 100%; tests with 100% specificity (no false positives) will have a positive predictive value (PPV) of 100%.

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