Introduction to Biostats Flashcards
Make that A boi
What is type 1 error?
Alpha error
Not accepting the null hypothesis when it is actually true and you should have accepted it
here really is no true differences between the groups being compared but you (in error) did not accept the Null Hypothesis thereby ultimately stating that you believe there is a difference between groups (when there really is NOT!)
What is kurtosis?
A measure of the extent to which observations cluster around the mean. for a normal distribution the value or kurtosis stastistic is 0
Positive kurtosis = more cluster
Negative Kurtosis = less cluster
What is Skewness?
A measure of asymmetry of a distribution
Perfectly normal distribution is symmetric and has a skewness value of 0
What is the interval or ratio level?
Interval
- Abritrary zero value (doesnt mean absence)
- Temperatire = 0 = freezing
Ratio
- Absolute (rational) zero value (0 means absence of meaurement) like physiological parameters
Yes order or magnitude
Yes consistency of scale or equal distances
Ex: living siblings (number) , personal age (in years) , blood pressure, Heart rate, Speed, amount of LDL
What are the required assumptions of interval/ratio data ? (for proper selection of a parametric test)
- Normally distrubted
- equal variances
- multiple test availble to assess for equal variances between groups
- LEVENEs TEST
- Randomly derived and independent
What other ways to look at interpretation of preset value?
- The probability of making a type 1 error, if the null hypthesis is rejected
- Probability of erroneously claiming a difference between groups when one does not really exist
- Probability of obtaining group differences as great or greater if the groups were actually the same /equal
- Probabiltt of obtaining a test statisitc as high/higher if the groups were actually the same or equal
What are the three important steps in sample size determination?
- Minimum difference between groups deemed most significant
- smaller the difference b.w groups necessary to be consdered significant or importantm the greater the sample size (N) needed
- Expected variation of measurement
- KNown or estimated from past studies/ populations
- Alpha (type 1) and beta (type 2) error rates and confidence internval (usually ranged from 90% to 99%)
What is a confidence interval?
CI’s are a value that describes both stastical significance and spread
Based on variation in sample (v/SD) and sample size (n)
journals are moving away from soley reporting P values or even showing them at all
How do you intreprete confidence intervals?
If the CI crosses 1.0 for ratios (OR/RR/HR)
or
0.0 for absolute differences = NOT SIGNIFICANT
What is type 2 error?
Beta error
Accepting the null hypothesis when it is actually false and you should have not accepted
There really IS a true difference between the groups being compared but you (in error) accepted the Null Hypothesis thereby ultimately stating that you believe there is no difference between groups (when there really IS!)
how can the levels of measurement of data change?
After Data is collected we can appropriately go down in specificity/detail of data measurement (levels) but never Up!
What are the three primary levels or groupings based for variables and there three key attributes? ***
NOMINAL
ORDINAL
INTERVAL or RATIO
3 Key attributes
- Order/magnitude
- Consistance of scale / equal distances
- Rational Absolute zero
What is the levenes test?
It is a test used to access weter variences are equal b/w groups. Its goal is to find signficant difference between two compared group
What is standard deviation (SD) ?
square root of variance value (restores units of mean)
What is variance (from mean) ?
The average the squared-differences in each individual measurement value (x) and the groups’ mean (x)
What is a negatively skewed data distrIbitution?
Asymmetrical distribution with on tail longer than another .
A distribution is skewed anytime median differs from the mean.
Negativly skewed = Mean is lower than the median.
tail points to left .
What is a positively skewed data distribution?
Asymmetrical distrubution wiht on tail longer than another.
A distrubution is skewed anytime the median differs from the mean.
Positively skewed occurs when mean is higher than median.
tail points right
What describe characterisitcs of graph whose data is normally distributed?
Normally distrubted = symmetrical
MEan and median are equal or near equal
Statstical test useful for symmetrical data are called parametric
What type of variable can be described as Ordinal?
Yes order or magnitude
No consistency of scale or equal distances
there categories remain rankable but there NO consistance scale of measure from one category to the next
Ex:
Pain scale - there is no consistant or measurable difference between happy or sad from person to person. The level of sadness that someone registers is different from another person.
