3. Basic Statistics I Flashcards
Why are central tendency measures useful in vet med?
Help you understand and critically evaluate the medical research literature
Understand patients values in relations to larger population
Understand biological variability
Mean
Sum of observations/ number of observations
Median
The level below or above half of the observations fall
Calculating median
Arrange in numerical order count how many values
If odd decide by 2 and round up to get position of median number
Even = decide by to go to the number in that position and average it with the number next highest
Mode
Most frequent occurance
calculating mode
Arrange in numerical order and number that appears most is the mode can have more than one
Example: do mean median mode of 1,1,2,3,4,5,24
Notation for population mean
“U” or mu
Notation for population standard deviation
sigma= o
Sd
Notation for population variance
Sigma squared
O^2
Normal and positive and negative skewed distributions
When to use median vs mean?
Median is better than mean for skewed date
Outliers can greatly skew the mean
What direction is skew?
In the direction of the tail
Can be negative or positive
What is probability
The numerical expression of the likelihood of occurrence
Simple conditional probability
At the likelihood of one event occurring
Conditional probability
Looks at two events occurring in relation to one another it looks at the probability of a second event occurring based on the probability of the first event occurring
Complex probability
Used to calculate the probabilities of independent events
Independent events
Those events whos occurance is not dependent on any other event
Mutually exclusive events
Events that cannot occur at the same time
Multiplication rule
Is used to calculate the probability of independent events both occurring
A and B
Pr = Pr (a) x Pr (b)
Addition rule
Used to calculate the probability of independent events either occurring
A or B
Pr = Pr (a) + pr (b)
Target population
The population to which it might be possible to extrapolate results from a study
Study/source population
The population from which the study subjects are drawn
Sampling frame
Are avalible and we are able to sample
Sample
Consists of individuals that end up in the study
Measurement error
Goal of designing a study is to accurately reflect your population of interest
All measurement susceptible to error
What are the two types of measurement errors
Random error (imprecision)
Systemic error (bias)
Sampling error
Is a bias in which a sample is collected in such a way that some member of the intended population have a lower or higher sample probability and others
Bias
How can you reduce systemic bias
Through random sampling giving everyone equal chance to be choosen
What are the 4 types of random sampling
Simple random sample
Systematic sample
Stratified sample
Cluster sample
Random sampling
Attempts to replicate the characteristics of the target population using a sample
Unbiased random sampling does not guarantee a replication of the target population characteristics
Standard error of measurement
Random error
Variability of a sample statistic
Sources = natural imprecise individual differences
Systematic error vs random error
Confidence intervals
Surround point estimate with marginal error
Confidence level
Is a measure of a degree of reliability of a confidence internal
Higher confidence level more strongly we believe that the true value of the parameter being estimated lies within the interval
