WEEK 9: STATISTICS

Question 1

What is biostatistics

Answer 1

is the science of analyzing data and interpreting the results so that they can be applied to solving problems related to biology, health, or related fields

Question 2

what is univariate analysis

Answer 2

describes one variable in a data set using simple statistics like counts (frequencies), proportions, and averages

Question 3

what is bivariable analysis

Answer 3

uses rate ratios, odds ratios, and other comparative statistical tests to examine the associations between two variables (mostly exposure and outcome)

Question 4

what is multivariable analysis

Answer 4

analysis encompasses statistical tests such as multiple regression models that examine the relationships among three or more variables

Question 5

what is a variable

Answer 5

Any quantity that varies from one entity to another (sometime within an entity over time)
- any attribute, phenomenon or event that can have different values

Question 6

what are the 2 types of variables

Answer 6

quantitative and qualitative

Question 7

nominal variables (qualitative)

Answer 7

• no intristic or logical order or value
• ex. university programs
• you can assign numbers to a different categories
• do not have any other numeric properties

Question 8

ordinal variables (qualitative)

Answer 8

Intrinsic value but with no clear or equal differences between levels (a set of ordered categories)
- ex. mild vs. moderate vs. severe pain
- rating scales

Question 9

3 ways to display qualitative data (nominal, ordinal)

Answer 9

pie chart, bar chart, frequency tables

Question 10

numeric variable (quantitative)

Answer 10

• any positive real number, depends on the nature of the variable can be expressed in decimals
• meaningful numeric scales
• age, blood pressure, # of friends, temperature
• assigned numbers have total mathematical meaning

Question 11

continuous variable

Answer 11

• can take any value within a range
• ex. a persons height. can be 60 inches
• blood pressure, temp.
• plotted as. a line

Question 12

discrete variable

Answer 12

• can take a finite or limited number of values
• not continious
• a family can not own 10 1/2 cars
• age in year, number of drinks
• can be plotted as dots

Question 13

quantitative variables: interval vs ratio

Answer 13

interval:
- difference is meaningful
- no natural zero

ratio:
- ratio is meaningful
- zero means absense of attribute (is natural)

Question 14

Mean

Answer 14

is calculated by adding up all the values for a particular variable and dividing that sum by the total number of individuals with a value for the variable=arithmetic average

Question 15

median

Answer 15

is the value in the middle when you rank the data in ascending or descending order
- Divides the data into 2 equal parts

Question 16

Mode

Answer 16

the most frequently occurring value for a particular variable in a data set

Question 17

histogram

Answer 17

a graph that shows the frequency of numerical data using rectangles
- important to manage the intervals

Question 18

range

Answer 18

range for a variable is the difference between the minimum (lowest) and the maximum (highest) values in the data set

Question 19

what are quartiles

Answer 19

mark the three values that divide a data set into four equal parts

Question 20

what is the interquartile range

Answer 20

captures the middle 50% of values for a numeric variable

Question 21

standard error of the mean

Answer 21

adjusts for the number of observations in the data set by dividing the variance by the total number of observations and then taking the square root of that number

Question 22

confidence intervals

Answer 22

Provide information about the expected value of a measure in a source population based on the measured value in a study population
- a larger sample size will yield a narrower confidence interval

Question 23

what does a 95% confidence interval mean

Answer 23

interval is usually reported for statistical estimates, which means that 5% of the time the confidence interval is expected to miss capturing the true value of a measure in the source population

Question 24

inferential statistics

Answer 24

Techniques that use statistics from a random sample of a population to make evidence-based assumptions (inference) about the values of parameters in the population as a whole

Question 25

null hypothesis

Answer 25

there is no difference between the two or more values being compared

Question 26

alternative hypothesis

Answer 26

there is a difference between the two or more populations being compared

Question 27

steps in hypotheis testing

Answer 27

1. Take a random sample from the population of interest
2. Set up two competing hypotheses (based on research questions)
3. use sample stats (mean, frequency) to decide whether to support or reject null
4. determine if the null hypothesis is really true, what the observed sample statistics will be

Question 28

p value

Answer 28

Introduced by Fisher to determine whether the observed sample supports the null
- between 0.1 and 0.9: no reason to suspect null hypothesis is false
- 0.05 the convention commonly used in health research

Question 29

how is p value calculated

Answer 29

from observed data based on pertinent test statistic

Question 30

if p = 0.01 what does this mean

Answer 30

If p=0.01 it means if in the real-world null is true (no difference) there is only 1% chance that the data produce results on a difference

Question 31

what is the significance level

Answer 31

is the p value at which the null hypothesis is rejected, usually 0.05 in health research

Question 32

parametric test

Answer 32

assumes the variables being examined have particular distributions
- Inferential methods are based on types of distributions (mostly normal)

Question 33

nonparametric test

Answer 33

does not make assumptions about the distributions of responses
- Nonparametric tests are used for ranked variables and when the distribution of a ratio or interval variable is non-normal

Question 34

bar chart and pie chart

Answer 34

Bar Chart - graph that presents categorical data with rectangle lengths proportional to the values they represent
Pie Chart - circle in which each wedge or slice displays the percentage of participants who provided a particular answer to 1 question

Question 35

kurtosis

Answer 35

describes how peaked or flat a bell-shaped distribution is

Question 36

leptokurtic vs playkurtic

Answer 36

Leptokurtic - distribution curve is very peaked
Platykurtic - curve is relatively flat

Question 37

unimodal and bimodal

Answer 37

Unimodal - has 1 peak
Bimodal - has 2 peaks

Question 38

standard deviation

Answer 38

the square root of variance

Question 39

z score

Answer 39

is a # that indicates how many standard deviations away from the sample mean the response of an individual from within that population
ex. a person who is the mean age has a z score of 0. A person whose age is 1 standard deviation above the mean in the population will have a z score of 1

Question 40

fabrication, falsification and plagirism

Answer 40

Fabrication - creation of fake data (creating fictitious data in a spreadsheet for people who never completed a questionnaire or ever participated in an experiment)
Falsification - misinterpretation of results (modifying extreme values to improve the results of statistical tests, manipulating photographs, or intentional misreporting a study’s methods to make the study look more rigorous)
Plagiarism - the use of other people’s ideas, words, ot images w/out permission and proper attribution

Question 41

outlier

Answer 41

value in a numeric data set that is distant from other observations and outside the expected range of values

Question 42

Steps for identifying a statistical test

Answer 42

1. Select variables to compare
2. specify the goal of the test
3. Check variable types
4. Choose appropriate test for variables
5. Confirm that assumptions of the test are met
6. Run test and interpret results

Question 43

Fisher’s Exact Test

Answer 43

compares the values of of a binomial variable in 2 independent populations