Lecture 6 - Biostatistics Part 2-2

Question 1

Look at the table on slide 3… VERY IMPORTANT TO UNDERSTAND

Answer 1

Did you do it… seriously did you do it?

Question 2

Measures of Central Tendency

Answer 2

Mean - the “average” – sum of the set divided by the number in the set

Median – the middle point (arrange the data smallest to largest, then find the middle point)

Mode – the score that occurs most frequently in a set of data
—–May have two most common values = “bimodal distribution”

Question 3

quantifies the amount of variability, or spread, around the mean of the measurements.

To calculate: take each difference from the mean, square it, and then average the result

Answer 3

Variance (σ2 ):

Question 4

a measure of variation of scores about the mean

Answer 4

Standard deviation (σ):

Question 5

To calculate: take the √ of the variance

the “average distance” to the mean

Answer 5

Standard deviation (σ):

Question 6

In practice, the standard deviation is used more frequently than the variance.
T or F?

Answer 6

True

Question 7

Heterogeneous group vs homogeneous group?

Answer 7

When comparing two groups, the group with the larger standard deviation exhibits a greater amount of variability (heterogeneous) while the groups with smaller deviation has less variability (homogeneous).

Question 8

Evaluates the strength of linear relationships or associations between variables

X increases and Y increases = positive correlation
X increases and Y decreases = negative correlation
0 is no correlation

Answer 8

Scatterplots

Question 9

The statement that establishes a relationship between variables being assessed

Example: In a clinical trial the hypothesis states the new drug is better the placebo

Answer 9

Alternative hypothesis (Ha or H1)

Question 10

The statement of no difference or no relationship between the variables

Example: In a clinical drug trial the null hypothesis states that the new drug is no better than placebo

Answer 10

Null hypothesis (Ho)

Question 11

More important than p value – a better determination of significance

Answer 11

Confidence interval (CI)

Question 12

Any statistic is simply an estimate of the true value of that statistic

Answer 12

Confidence interval (CI)

Question 13

_____ produces a range within which the true value most likely lies

Answer 13

Confidence interval (CI)

Question 14

95% CI states that we can be 95% certain that the “true” value is within the CI range

Meaning what is better?

Answer 14

Narrower CI is better

Question 15

If the CI include 1 (null value) then the results are…

Answer 15

clinically insignificant

Question 16

______ is used to separate from a large group of apparently well persons those who have a high probability of having the disease, so that they may be given a diagnostic work up, and if diseased can be treated.

Answer 16

A screening test

Question 17

In general, screening is performed only when the following conditions are met:

Answer 17

The target disease is an important cause of mortality and morbidity.

A proven and acceptable test exists to detect individuals at an early stage of disease.

There is a treatment available to prevent mortality and morbidity once positives have been identified.

Question 18

The proportion of people with the disease who have a positive test for the disease.

Answer 18

Sensitivity

Question 19

The ability of the test to identify correctly those who have the test.

Answer 19

Sensitivity

Question 20

– The proportion of people without the disease who have a negative test.

Answer 20

Specificity

Question 21

The ability of the test to identify correctly those who do not have the disease

Answer 21

Specificity

Question 22

A test with high _____ will not miss many patients who have the disease

Answer 22

sensitivity

Question 23

A highly useful test when NEGATIVE

Answer 23

sensitivity

Question 24

Screening test’s ability to identify presence of disease

Answer 24

Sensitivity

Question 25

Tends to rule OUT the disease

Answer 25

Sensitivity

Question 26

High ____ means low probability of false negative

Answer 26

Sensitivity

Question 27

Screening test’s ability to truly identify absence of disease That is, how likely is a negative test actually reporting the right answer?

Answer 27

Specificity

Question 28

A highly useful test when it is POSITIVE

Answer 28

Specificity

Question 29

Tends to rule IN the disease

Answer 29

Specificity

Question 30

High _____ means low probability of false positive

Answer 30

Specificity

Question 31

In practice, a compromise is reached and the cutoff point is set, leading to false-positives and false-negative results.

Answer 31

In a single test sensitivity may be increased but only at the expense of specificity, and similarly specificity may be increased at the expense of sensitivity.

Question 32

In a single test sensitivity may be increased but only at the expense of ______

Answer 32

specificity, and similarly specificity may be increased at the expense of sensitivity.

Question 33

A highly sensitive test is most useful to the clinician when it is

Answer 33

NEGATIVE

Question 34

A highly specific test is most useful to the clinician when it is

Answer 34

POSITIVE

Question 35

read slides 19-23 and make sure you can interpret the data correctly

Answer 35

it's only your grade dummy

Question 36

Sequential (Two-Stage) Testing Allows us to calculate the net sensitivity and net specificity of using both tests in sequence. After completing both tests there is a loss in.....

Answer 36

net sensitivity and net gain in specificity.

Question 37

in ________, a less ex­pensive, less invasive, or less uncomfortable test is generally performed first, and those who screen positive are recalled for further testing with a more expensive, more invasive, or more uncomfortable test, which may have greater sensitivity and specificity. It is hoped that bringing back for further testing only those who screen positive will reduce the problem of false positives.

Answer 37

Sequential (Two-Stage) Testing

Question 38

= proportion of patients who HAVE the disease and a positive test

Answer 38

Positive Predictive Value (PPV)

Question 39

= proportion of patients who DO NOT HAVE the disease, and have a negative test

Answer 39

Negative Predictive Value (NPV)

Question 40

Percent of patients with positive test who actually have the disease

Answer 40

Positive Predictive Value (PPV)

Question 41

Assesses reliability of positive test | i.e. PPV 90% = positive test 90% of the time the test is correct

Answer 41

Positive Predictive Value (PPV)

Question 42

With low prevalence (% of population) of disease:

Answer 42

Lower PPV False positives increase Less reliable positive test result

Question 43

Percentage of patients with a negative test who actually do NOT have the disease

Answer 43

Negative Predictive Value (NPV)

Question 44

Assesses reliability of a negative test | i.e. NPV 90% = negative 90% of the time the test is correct

Answer 44

Negative Predictive Value (NPV)

Question 45

With low prevalence(% of pop) of disease :

Answer 45

Higher NPV False negative test decreased A negative test result is more reliable

Question 46

________- the occurrence, rate, or frequency of a disease Obtained from cohort studies Must follow a cohort through time

Answer 46

Incidence

Question 47

Incidence is obtained from?

Answer 47

cohort studies in which a cohort was followed throughout time

Question 48

______the number of occurrences at one particular time Obtained from cross-sectional studies No time line, only a snap shot

Answer 48

Prevalence

Question 49

_____ is obtained from cross-sectional studies (no timeline)

Answer 49

prevalence

Question 50

slide 34.... Relationship between Incidence and Prevalence

Answer 50

understand it

Question 51

How does a treatment that prevents death effect incidence or prevalence?

Answer 51

the incidences don't increase or decrease, but the prevalence does because people aren't dying

Question 52

A method of predicting change in the dependent variable by changing one or more independent variables

Answer 52

Regression analysis

Question 53

Allows the researcher to explore the relationship between two continuous variables

Answer 53

Regression analysis

Question 54

What % of variation in the dependent variable can be explained by a change in the independent variable

Answer 54

Regression analysis Example: when you GAIN 8 pounds, your SBP can be expected to increase by ~6 mmHg Or, if you LOSE 8 pounds, your SBP can be expected to DROP by ~6 mmHg

Question 55

Four types of Data:

Answer 55

``` Four types: Categorical ---Nominal ---Ordinal Continuous ---Interval ---Ratio ```

Question 56

Categorical Data _____ named categories with no implied order ----Gender, race, ABO blood type, group

Answer 56

Nominal

Question 57

Categorical Data _____ sequenced or ranked data -----Smallest to largest, lightest to heaviest, easiest to most difficult

Answer 57

Ordinal

Question 58

Continuous Data _____ intervals along the scale are equal to one another (i.e. integers) Set on an underlying continuum that allows you to talk about how much higher one value is than another 0 on the scale does not mean the absence of the item (e.g., degrees Fahrenheit)

Answer 58

interval

Question 59

Continuous Data ______ characterized by the presence of absolute zero on the scale An absence of any of the trait being measured (e.g. weight) Most precise

Answer 59

Ratio-

Question 60

what is the most precise form of data?

Answer 60

A ratio of continuous data