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epi biostats review
epi biostats review
124
Other
Graduate
12/11/2009

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Term
classification of variables into different categories. serve as an ID only. ex- "what is your name"
Definition
nominal
Term
when the amount of variable is placed in order of magnitude. No zero value. differences between the items can vary.
Definition
ordinal
Term
ordinal measurement but the differences between the scores are equal. with this there is equal differentiation between each variable.
Definition
interval
Term
measurement has a true zero point, absence of that variable. ex- "you do not have cancer"
Definition
ratio
Term
measurable or countable data
Definition
quantitative
Term
ordinal and nominal data are...
Definition
categorical
Term
ordered categories. grade of breast cancer. better, same, worse. disagree, neutral, agree
Definition
ordinal
Term
unordered categories. sex, alive or dead, blood group O,A,B,AB
Definition
nominal
Term
the set of all possible values for the variable.
Definition
a statistical population
Term
a subset of the population
Definition
sample
Term
a sample in which each member of the population has an equal probability of entering the sample
Definition
simple random sample
Term
sampling...
Definition
-necessary if inferential statistics are to be used
-need to be representative
-random sampling
Term
exclusion of a subset of the population of interest prior to sampling
Definition
selection bias
Term
introduced when responses are not obtained from all sample members
Definition
nonresponse bias
Term
inaccuracy in recorded data. can be due to survey design, interviewer impact.
Definition
measurement error
Term
transcription error, data corruption
Definition
processing error
Term
a complete set of people, events, etc. that share a common characteristic. the scientific notation for this is "N".
Definition
population
Term
a subset or subgroup that should be representative of the entire population. the scientific notation for this is "n".
Definition
sample
Term
the number that summarizes or describes a characteristic of a population
Definition
parameter
Term
the variable that is manipulated in an experiment to determine its effect on the dependent variable. what you can control.
Definition
independent
Term
the variable that depends on the independent variable. this is often a measure of behavior or outcome. this is what is being measured.
Definition
dependent
Term
the characteristic of an individual population unit
Definition
variable
Term
generalization about a population based on sample data. ex- the average age on admission is 21.9. (making an assumption about the population)
Definition
statistical inference
Term
statement about the uncertainty associated with an inference
Definition
measure of reliability
Term
a statistic that compares a numerical description of two sets of data and the direction of the relationship. (how "a" is related to "b".) only two variables, not three.
Definition
correlation coefficient
Term
a statistical method of predicting one set of values from another set of measured values. more than two variables.
Definition
regression analysis
Term
data with absolute zero (zero means no value)ex- bank account when you are down to nothing,...no negatives allowed.
Definition
ratio data
Term
data with relative zero (zero has value). the difference between 0 and 1 is the same difference as 1 and 2. negatives ARE allowed.
Definition
interval data
Term
three main aspects of a distribution of data...
Definition
shape (look at graphs)
center (what number is in the middle)
spread (how much variation)
Term
number of data points in a class
Definition
class frequency
Term
class frequency/ n=
- m & m example= green/ total number of m & ms
Definition
class relative frequency
Term
class relative frequency x 100
Definition
class percentage
Term
number of intervals...
Definition
10-20. general rule of thumb= there should be no fewer than 6 intervals, and no more than 15.
Term
this is found by dividing the difference between the largest and smalles score by the number of class intervals (w=R/k)
(size of intervals/ over how many intervals we want)
Definition
size of intervals
Term
a way to show what your data looks like. a graphic display. your "stem" is the midpoint.
Definition
stem-and-leaf display
Term
a distribution that when folded in half, produces two identical shapes.
Definition
symmetry
Term
a distribution in which scores are clustered at one end, and rarity of scores occur on the other end.
Definition
skewness
Term
if the tail (rare scores) occurs for the high scores to the right.
Definition
positively skewed
Term
if the tail (rare scores) occurs for the low scores to the left
Definition
negatively skewed
Term
tendency of data to center about certain numerical values. mean, median and mode.
Definition
central tendency
Term
the score that occurs the most often (can be unimodal, bimodal, or multimodal) data displayed in a histogram will have a modal class- the class with the largest frequency
Definition
mode
Term
the score with an equal amount of scores above and below it (50th percentile)middle number when observations are arranged in order. not always the number in the middle
Definition
median
Term
the sum of scores divided by the number of scores (average)
Definition
mean
Term
the spread of the data across possible values.
Definition
variability
Term
largest measurement minus the smallest measurement. this loses sensitivity when data sets are large.
Definition
range
Term
may provide a better way of describing the variety that exists among the values in a data set. involves measuring dispersion relative to the scatter of values in a data set about their mean.
Definition
variance
Term
provides a measure of dispersion in original units by simply taking the square root of the variance. useful as a measure of variation within a given set of data
Definition
standard deviation
Term
s
Definition
standard deviation
Term
the square root of the sample variance
Definition
sample standard deviation
Term
the square root of the population variance
Definition
population standard deviation
Term
a standard deviation
Definition
a z-score
Term
descriptive measures of relationship of a measurement to the rest of the data
Definition
common measures:
percentile ranking or percentile score
z-score
Term
the distance between a measurement x and the mean, expressed in standard units. this allows comparison across data sets.
Definition
z-score
Term
an observation that is unusually large or small relative to the data values being described
Definition
outlier
Term
you will be able to tell the 25%, 50%, and 75% percentile in this. AKA "box and whiskers plot"
Definition
box plots
Term
box plot formula...
Definition
take number at 75% percentile - number at 25% percentile= 50% percentile number. (slide 52 on presentation 2)
Term
the range of values for the middle 50% of the scores in a distribution
Definition
interquartile
Term
anything + or - 3 outside of deviations
Definition
outliers
Term
correlation that moves up and to the right...
correlation that moves down and to the right... (on scattergram)
Definition
-positive coorelation
-negative coorelation
Term
look up pareto diagram picture
Definition
pareto diagram
Term
everytime you see this value, someone has tested a hypothesis.
Definition
p-value
Term
by chance the group's results were different...
Definition
random variation
Term
the two treatment arms really had different results
Definition
true difference
Term
the two groups were chosen poorly and are different for reasons that have nothing to do with the treatment
Definition
sampling error or bias
Term
in research, you are trying to reject this, then you have a relationship. "there is no difference between the two study groups" statistical testing is always done as an exercise to disprove this hypothesis.
Definition
null
Term
There is a difference in this hypothesis.
Definition
alternate hypothesis
Term
there is a difference but not saying which direction
Definition
two tailed alternate hypothesis
Term
"a" is better than "b"
Definition
one-tailed hypothesis
Term
if p-value is LESS than alpha..
look at slide 21 in hypothesis testing lecture!
Definition
statistically significant
if p=.10 and alpha=.05= NOT SIGNIFICANT
Term
Standard deviations....
Definition
+/-1= 68%
+/-2= 95%
+/-3= 99.7%
Term
if p value is equal to alpha, is it statistically significant?
Definition
yes, as long as it is the same or smaller than alpha, it is statistically significant
Term
when we falsely reject the null hypothesis, we have committed a __error.
Definition
type 1 (alpha)
Term
when we falsely fail to reject the null hypothesis, we have committed a __error.
Definition
type II (beta)
Term
significant tests for data form interval or ratio scales. they are more powerful than nonparametric tests. they are preferred if their assumptions are met.
Definition
parametric tests
Term
used to test hypotheses with nominal and ordinal data
Definition
nonparametric tests
Term
an advantage for nonparametric tests...
Definition
appropriate for non-normal population distributions
Term
in this you know the whole population.
Definition
z test
Term
in this you have to use probability. has more tail area than in a normal distribution.
Definition
a t-test
Term
this test is used when you are testing for differences between samples. it is the measure of the differences between actual and expected frequencies. it is a test of association between two categorical variables. used with either nominal or ordinal measurements.
Definition
chi-square test
Term
estimates the standard deviation of the difference between the measured values and the true values. "how close is the sample mean to the population mean?"
Definition
standard error
Term
the population or true mean
Definition
expected value
Term
the average of your sample
Definition
observed mean
Term
a measure of spread
Definition
standard error
Term
n-1 (number of values used to calculate SD or SE)
Definition
degrees of freedom
Term
the theorem that the distribution of sample means taken from a large population approaches a normal (Gaussian) curve. tells us how much error to expect in our sample estimates.
Definition
central limit theorem
Term
you are comparing the MEANS of two groups. use this because you can't use a Z. very common.used when the standard deviation of the population is NOT known
Definition
t-test
Term
this is a measure of the difference between your data and what you expect to see, in units of standard error.
Definition
t
Term
Testing the means of 3 or more groups of continuous, normally distributed data to see if they are all equal to one another...for this we would use an entirely different test called....
Definition
analysis of variance, AKA ANOVA
-You use F stat
Term
if you have categorial data, you will use this...
- has cells
Definition
chi-square
Term
standard error is a predictor of what?
Definition
standard deviation
Term
do you want a high or low chi square statistic?
Definition
you want high= more significant
Term
calculation of chi-square degrees of freedom. ex- 5x3 contingency table would have__df.
Definition
(number of rows-1) multiplied by the (number of columns - 1)
answer= 8
as df rises, so does probability.
Term
when you have 2 proportions that are NOT equal, you will have this..
Definition
two-sided test (two tailed)
Term
if your p value is .09, which is greater than .05 alpha...
Definition
it is NOT significant
-you CANNOT reject the null
Term
-used to analyze multi-level designs
-method for testing hypotheses about differences between 3 or more sample means.
Definition
analysis of variance, ANOVA
Term
ANOVA overcomes this problem...
Definition
enables the researcher to detect significant differences between the treatments as WHOLE. All treatments have similar variance.
Term
-factors are independent variables. (A is not related to B is not related to C)
-Variables are categorical and must define separate gropus
Definition
ANOVA
Term
ANOVA test provides an___statistic which is used to calculate the p-value.
Definition
F-statistic
Term
ANOVA is a combination of __ tests.
Definition
T
Term
When you have one outcome and you are trying to explain it. you plug all of these variables in, and it will give you predicted value. The value of one variable can be PREDICTED if the value of the other variable is known. starts at the top, and moves down variable by variable.
Definition
regression analysis
Term
Your predictor variable/ explanatory variable
Definition
independent (turkey is independent variable- turkey leads to fatigue)
Term
predicted variable
Definition
dependent (fatigue= dependent when you eat turkey you will experience fatigue)
Term
the magnitude of the slope of the line represents...
Definition
the amount that the dependent variable changes for each unit changed in the independent variable
Term
the magnitude of the slope is represented by this value
Definition
correlation coefficient
Term
range for correlation coefficient...
Definition
-1 to 1.
values of 0-0.25 indicates little or no relationship between two variables
->0.75 reflect a strong relationship
Term
refers to generalizability of the results obtained from the study
Definition
external validity
Term
refers to METHODOLOGY utilized in the study. can either overestimate or underestimate the true association between exposure and outcome.
Definition
internal validity
Term
three general categories of threats to internal validity..
Definition
-chance
-bias
-confounding
Term
"any systematic error in design, conduct or analysis of a study that results in a mistaken estimate of an exposure's effect on the risk of disease.
Definition
bias
Term
misclassifying exposure or outcome status. there is not a set scale (ex- vigorous exercise is interpretted differently among different people) SUBJECTIVE
Definition
misclassification bias
Term
Classifying some of the subjects as having had an MI when they did not...
Definition
outcome misclassification
Term
misclassification that occurs in the same proportion in each group being studied...
Definition
random or nondifferential misclassification (DO NOT MATCH NON-RANDOM AND NONDIFFERENTIAL,....NO NON NON)
Term
misclassification that occurs in different proportions in each group
Definition
non-random or differential misclassification (DO NOT MATCH NON-RANDOM AND NONDIFFERENTIAL..NO NON, NON)
Term
Always results in an underestimation of the true association, you have just accepted the null
Definition
random misclassification
Term
misclassification can either overestimate or underestimate the true association, depending on the situation.
Definition
non-random or differential misclassification
Term
occurs when one group is followed more closely than the other group...non-random misclassification (unproportionally giving more attention to one group verses another)
Definition
surveillance bias
Term
a potentially relevant exposure may be remembered by a "case" and be forgotton by a "control". (ex- people who were actually diagnosed with melanoma have more emotional involvement)NON-RANDOM
Definition
recall bias
Term
-they lie/ do not remember
-subjects may not be willing to report an exposure accurately. RANDOM(everybody lies)
Definition
reporting bias
Term
data collection methods differ between groups. results in a non-random misclassification. in a case control study, one interviewer may ask more probing questions
Definition
interviewer bias
Term
the way in which cases and controls, or exposed and non-exposed individuals are selected is such that an apparent association is observed even when in reality, the exposure and the disease is not associated
Definition
selection bias
Term
this occurs when 2 conditions are met.
-there must be an association between a variable (third factor) and the exposure status
-the variable must also be an independent risk factor for the outcome
Definition
confounding
Term
does NOT invalidate study results.
-need to account for it
-if not identified, may result in a missed opportunity to not differences in outcomes between subgroups in a study. answers the question "is the relationship between the exposure and the outcome the same or different across various strata or subgroups, within the study?
Definition
effect modification
Term
when doing a study...
Definition
the aim is to control confounding and elimate its effects
-effect modification is to be described and reported
Term
the magnitude or direction of an association varies according to levels of a third factor.
Definition
effect measure modification
AKA "effect modification" and "interaction"
unlike confounding, effect measure modification should be described and reported, rather than controlled
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