Intro to Biostats--Lectures 1&2 Flashcards
What is the first step to take when developing research
Develop a hypothesis
What are the 4 steps of hypothesis testing
- Formulate a hypothesis
- Set criteria for decision
- Gather data and conduct statistical analysis
- Make decision (accept or reject)
What is a null hypothesis
States that two variables are not related
What are the two types of hypothesis used in hypothesis testing
Null hypothesis
Alternative hypothesis
What does a null hypothesis assume
no difference
all samples from some population
observed difference is due to chance
random sampling variation
What does an alternative hypothesis assume
at least one sample is from a different population
difference is not due to chance
How do you use a null hypothesis for testing
You try to disprove H0
If the probability of our result is less than alpha, then what is unlikely
that all samples came from the same population
What is alpha normally
0.05
When is a blood count considered normal
if value is found in 95% of the population and if independent of other tests
What are the two types of probability
mutually exclusive
independent
What is mutually exclusive probability
only one event can occur
either or
not both
What is independent probability
both things occur independently so you can have both
one even has no effect on the occurence of the other
How do you calculate mutually exclusive probabilities
addition rule
probability of X + probability of Y
How do you calculate independent probabilities
multiplication rule
probability of X x probability of y
What is sampling in statistics
selection of study subjects who will be measured on some parameter to provide information about population
What are the different sampling techniques
simple random stratified systematic multistage convenience
What is the ultimate goal in sampling
want to avoid selection bias
What is selection bias
not giving people an equal chance to be selected
How is simple random sampling performed
each individual has an equal chance of having their name selected (draw names out of a hat)
How is systematic sampling done
select at regular intervals through ordered list
pick random number (k) and select kth person
What is stratified sampling
Separate people into strata and then select a sample from each group
keep the proportion of participants from each stratum equal
What is multistage sampling
combines more than 1 sampling
surveys sent out to randomly selected sample; from those answers select a more detailed survey
What are the types of variables based on how data is measured
Qualitative, quantitative
What are the variables based on study design
dependent and independent
What are the different types of qualitative (categorical) variables
Nominal
Dichotomous
Ordinal
What are nominal variables
multiple categories with no difference in quality
What are dicotomous variables
only two labels for variable
What are ordinal variables
ranked variables
What are the different types of quantitative variables
Interval
Ratio
What is an interval variable
any quantitative vale
What is a ratio variable
has meaning
What are independent variables
input; manipulated
What are dependent variables
outcome, response, predicted
What is the standard P value that should be used in hypothesis testing
P<0.05
What are the measures of central tendency
mean median mode
What are the measures of dispersion
range, interquartile range, percentiles, SEM, SD, kurtosis, skewness, Confidence interval, Power, errors
What is sample size and how does this affect statistical power
larger sample sizes tend to have more statistical power
How do mean and median relate to distribution of a data set
if the same= normal distribution
if not the same= not normal distribution
What is the function of descriptive statistics
describes data without generalizing population
What is variance
spread of data
What does 0 variance mean
identical values
What is range
highest and lowest values
What is interquartile range
difference between 25th and 75th percentiles
What is standard deviation
square root of the variance
How is standard error of the mean calculated
SD/ squareroot of sample size
What will the SEM be in bigger groups compared to smaller groups
larger n= smaller SE
How can we reduce variance
increase sample size
better define our sample populations
censor outliers
What are the different types of normal unimodal distributions
Gaussian Distribution
Bell-shaped curve
What are the different types of skewed unimodal distributions
left-skewed
right-skewed
Describe a normal bell-shaped curve
1 standard deviation above and below the mean will include 2/3 of the data
95% will be within 2 standard deviations above and below the mean
What is a skewed distribution
mean not equal to median
What is a better measurement of the middle of the data in a skewed distribution
median
What is a positive skew
right tail is longer; most values near y axis
mean> median> mode
What is a negative skew
left tail is longer; most values on the right
mean< median< mode
What is kurtosis
the “peakedness” of the distribution
What is confidence interval
range of values in which a specified probability of the means of repeated samples would be expected to fall
What are the different types of error
Type 1 (alpha) Type 2 (beta)
What is a Type 1 alpha error
probability of rejection H0 when it is true
What is a Type 2 beta error
probability of accepting H0 when it is false
What is the probability of Type 1 error
false positive rate
What is the probability of Type 2 error
false negative rate
What is Power
probability of NOT committing Type II error
How is Power calculated
1-beta
