Biostatistics

Question 1

What is Biostatistics defined as?

Answer 1

-the application of statistical theory in medicine, public health, or biology

Question 2

Population

Answer 2

• large group of all subjects interest in a study.
• very large almost impossible to collect data from whole population
• have to select a subset of subjects to get samples from a population, then generalize findings from samples to the target population

Question 3

conceptual population

Answer 3

-population of persons people/ identity

Question 4

population in clinical setting?

Answer 4

-usually talk about it as population of measurements such as weight, height, and blood pressure

Question 5

Total population

Answer 5

• target population
• all of the subjects of interest in a study, about which the study wants to generalize the conclusion
• ex: all 12 year olds in US

Question 6

Defined population

Answer 6

• a subpopulation confined by certain characteristic(s) such as demographics and geographical areas in the total population
• ex: 12 year olds in RUSD

Question 7

Study population

Answer 7

The group of individuals in a study

• In a clinical trial, all participants who followed criteria of inclusions and exclusions make up the study population
• ex 12 year olds in certain school in RUSD

Question 8

Sample

Answer 8

• a procedure to select samples from the study population, they are representative of the total population
• validity based on how random and well rounded this sample group is

Question 9

How do we estimate the required sample size?

Answer 9

1) pre-determined power (80/90%)
2) specific significance level
3) mean & variance of the primary outcome; can be approximated
4) the design of the study

Question 10

what is a statistic?

Answer 10

• calculated from a sample for a specific characteristic of the sample
• will be used to estimate the corresponding parameter of the study population & further generalized to the target population to find mean & standard deviation

Question 11

Why do we sampling to get samples?

Answer 11

Money, Time, Practicality, and Accuracy

Question 12

Probability sampling

Answer 12

• each subject has a known probability of being selected
  1) simple random sampling
  2) stratified random sampling
  3) Systematic random sampling
  4) Clustered random sampling

Question 13

simple random sampling?

Answer 13

based on probability to take the samples

-each member of the subset has an equal probability of being chosen

Question 14

stratified random sampling?

Answer 14

• stratify the study population into subgroups, then take random samples from such subgroups
• ex: names of 25 employees being chosen out of a hat from a company of 250

Question 15

Systematic random sampling

Answer 15

• type of probability sampling
• members from a larger population are selected according to a random starting point and a fixed, periodic interval
• interval, is calculated by dividing the population size by the desired sample size

Question 16

Clustered random sampling

Answer 16

• the researcher divides population into separate groups (clusters)
• a random sample of clusters is selected from the pop
• researcher conducts his analysis on data from the sampled clusters

Question 17

non-probability sampling

Answer 17

• each subject doesn’t know probability of being selected, –stimations are biased
  1) voluntary samples
  2) convenience samples

Question 18

voluntary samples

Answer 18

-whoever is self selected into the samples

Question 19

convenience samples

Answer 19

-whoever is convenient to be selected and/or investigated. -ex: staff members in med school recruited for some trials

Question 20

Sampling errors

Answer 20

• random errors
• are unavoidable
• the differences between the sample & population, due to sampling randomness

Question 21

sampling errors effect on the data?

Answer 21

• Random error does not have consistent effects across the entire sample
• the sum would be zero if the sample size is large enough.

Question 22

what does sampling error add? what does it not affect?

Answer 22

-random error adds variability to the data but doesn’t affect average performance of the samples

Question 23

Non-sampling errors

Answer 23

• more serious due to mistakes made in the acquisition of data, inappropriate sample selection, or response biases
• can bias estimation

Question 24

Random Samples vs. Randomization

Answer 24

Both involve the use of the probability sampling method.

Question 25

Random sampling

Answer 25

• determines who should be included in the samples;
• related to sampling procedure;
• effect external validity (generalizability)

Question 26

Randomization or random assignment

Answer 26

• determines if sampled subjects should be in treatment or control group
• related to design operation
• effects internal validity

Question 27

how we can conduct correct population inferences from the sample data we have?

Answer 27

• mean and variance are the cornerstones for statistical inference
• used to estimate the corresponding values of population.

Question 28

1) letters used for population?

2) letters used for sample estimation?

Answer 28

1) greek letters

2) sample estimation

Question 29

How use an unbiased estimation of population variance?

Answer 29

• use n-1 instead of n in sample variance equation

- N (capital N) used for the population variance

Question 30

Standard deviation (SD)?

Answer 30

• measure of the variability of a measurement among the subjects in a population or in a sample
• can be estimated for both population & sample
• often unknown for pop. but can be estimated from SD of its samples

Question 31

Standard Error (SE)?

Answer 31

• measure of the precision of the sample mean
• decreases w/ increasing sample size
• estimated only for sample.

Question 32

In general what is reported when summarizing the sampling variation?

Answer 32

• SD (standard deviation)

- SE is given for any statistical inference of mean

Question 33

What is Outcome?

Answer 33

• a specific characteristic of interest being studied
• could be more than one
• also called endpoints
• can be described or quantified by different measurement scales

Question 34

Measurement scales (4)?

Answer 34

1) Nominal
2) Ordinal
3) Interval
4) Ratio

Question 35

Nominal

Answer 35

• Categorizing subjects by characteristics such as gender and ethnicity
• the categories have neither order or ranking
• neither logic nor mathematical operation

Question 36

Ordinal

Answer 36

• ranking subjects into different orders
• precise differences between ranks do not exist, and one rank is not better than other
• pain severity

Question 37

Interval

Answer 37

• quantitative measurement with equal units, every one unit difference is meaningful and constant,
• doesn’t have absolute zero point
• ex: temperature

Question 38

Ratio

Answer 38

• uses zero to present the absence of value (absolute zero point)
• ex: height, age, weight

Question 39

Qualitative data

Answer 39

• describe subjects in qualities, cannot measure subjects in precise quantities
• nominal scale and ordinal scale.

Question 40

Quantitative data

Answer 40

• quantify the quantities of the subjects, can be measured by scales or counted by numbers.
• can be discrete or continuous

Question 41

Discrete

Answer 41

• Reflect a number during the counting process, no decimal
• Zero is the minimum
• ex: number of children

Question 42

Continuous

Answer 42

Reflect a measurement with decimal places, often depends on the precision of the measuring device

Question 43

What does probability provide?

Answer 43

• a quantitative description of the chances (of successful treatment outcomes) or likelihoods (of disease) associated with various outcomes
• provides a bridge between sample statistics and population parameters

Question 44

what three components do you need to estimate probability?

Answer 44

1) outcome
2) sample space
3) an event

Question 45

outcome?

Answer 45

• a possible result from an experiment

- ex: toss coin get heads or tails

Question 46

Sample Space?

Answer 46

• the set of all possible outcomes of an experiment

ex: flip coin can be head or tails

Question 47

An Event?

Answer 47

• a subset of outcomes that are equally likely to take place, can be defined by one or more members of the sample space.
  ex: toss coin can be H/T; but if toss coin more than once can be HHT or TTH etc

Question 48

Empirical Probability ?

Answer 48

• estimated as the proportion of: how many times the event of interest occurred / the total number of all the potential events that might be observed
• epidemiology, is defined by empirical probability

Question 49

Marginal probability

Answer 49

the probability of an event occurring

Question 50

Conditional probability

Answer 50

• measure of the probability of an event occurring given that another event has occurred.
• important in medicine since disease is based on many factors

Question 51

Prevalence

Answer 51

• expressed & reported as a percentage, per 1000, or per million
• measure of disease burden in the population but not a measure of risk
• is a snapshot in time, but can use different time scales

Question 52

time scales used in prevalence calculations?

Answer 52

1) point prevalence (at a certain time point, most common)`
2) period prevalence (during a certain time period)
3) cumulative incidence (before a time point)

Question 53

what does incidence rate measure?

Answer 53

1) new cases in a population over a given period
2) risk of developing a disease within a given period
3) how quickly new cases develop in the population
- per 100; 100 million, or 1000
- also called absolute risk

Question 54

how are prevalence and incidence rate related?

Answer 54

-Prevalence= Incidence × Disease Duration

Question 55

how does a new treatment for lung cancer patients that prolongs survival effect the prevalence, incidence & disease duration?

Answer 55

1) prevalence increased
2) incidence unchanged
3) duration increased

Question 56

how does an effective AIDS vaccine created and approved

effect the prevalence, incidence & disease duration?

Answer 56

1) prevalence decreased
2) incidence decrease
3) duration unchanged

Question 57

how does a sensitive & early detection test is developed to diagnose cancer at earlier stages to make cancer relatively easy to control
effect the prevalence, incidence & disease duration?

Answer 57

1) prevalence increase
2) incidence increase
3) duration increase

Question 58

Mortality Rate

Answer 58

(𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑑𝑢𝑟𝑖𝑛𝑔 𝑎 𝑠𝑝𝑒𝑐𝑖𝑓𝑖𝑐 𝑝𝑒𝑟𝑖𝑜𝑑)/(𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑝𝑒𝑟𝑠𝑜𝑛𝑠 𝑖𝑛 𝑡ℎ𝑒 𝑝𝑜𝑝𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝑑𝑢𝑟𝑖𝑛𝑔 𝑡ℎ𝑒 𝑝𝑒𝑟𝑖𝑜𝑑

Question 59

Case fatality rate

Answer 59

• is a %

- (𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑒𝑎𝑡ℎ𝑠 𝑎𝑓𝑡𝑒𝑟 𝑑𝑖𝑠𝑒𝑎𝑠𝑒 𝑜𝑛𝑠𝑒𝑡 𝑜𝑟 𝑑𝑖𝑎𝑔𝑛𝑜𝑠𝑖𝑠)/(𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑡ℎ𝑒 𝑝𝑒𝑟𝑠𝑜𝑛𝑠 𝑑𝑖𝑎𝑔𝑛𝑜𝑠𝑒𝑑 𝑤𝑖𝑡ℎ 𝑡ℎ𝑒 𝑑𝑖𝑠𝑒𝑎𝑠𝑒) x 100