Basic Statistics Flashcards
What is an independent variable (IV)?
- variable examined to determine its effect on outcome of interest (DV)
- under control of experimenter - manipulated variable
e. g., dose of a drug
What is a variable?
measurable characteristic that changes with person, environment, experiment
e.g., blood pressure, A1c levels, cholesterol LDL/HDL levels
What is a dependent variable (DV)?
- outcome of interest measured to assess effects of IV
- not under experimenter control
e. g., how a person reacts to the drug
What is a subject, or organismic variable?
naturally occurring IV characteristic of people but not controlled
e.g., gender, race, BRCA1
What are the four different types of data?
- nominal
- ordinal
- interval
- ratio
What is nominal data?
- qualitative (name)
- mutually exclusive without logical order
e. g., types of physical activity a diabetic patient engages in - walking, swimming, hiking
What is ordinal data?
- qualitative
- mutually exclusive with logical rank ordering ()
e. g., ratings of how a patient feels: very poor, poor, average, good, very good
What is interval data?
- quantitative with equal units of measurement allowing for the distance between two pairs to be equivalent in some way
- there is an arbitrary (no meaningful) zero point
e. g., cancer patients rate their level of energy on a 1-10 scale
What is ratio data?
- quantitative with equal units of measurement where numbers can be compared as multiples of one another
- meaningful zero point
e. g., height, weight, length
What are the two different types of numbers?
- discrete/discontinuous data
- continuous data
What is characteristic of discrete data?
only whole numbers allowed
e.g., # of manic episodes in a week
What is characteristic of continuous data?
any values allowed
e.g., weight, height, fasting blood glucose levels
On which axis is the independent variable typically plotted on?
x-axis
On which axis is the dependent variable typically plotted on?
y-axis
What are some features of a bar graph?
- nominal, sometimes ordinal data
- each bar = category
- height = frequency (proportion or %)
- bars do not touch for categories (but if have two+ groups the groups within each category (males and females) can touch)
- if ordinal data, must preserve order
- can be vertical or horizontal
What are some features of a histogram?
- interval, ratio date; sometimes ordinal
- same rules as bar, BUT bars touch
- usually for discrete data
What are some features of a line/frequency graph?
- interval, ratio, sometimes ordinal data
- usually for continuous data
- points represent data and lines connect the data points showing the continuous nature of data (i.e., can have any value between)
What are the different forms of graphs?
- normal: bell-shaped or symmetric about a line drawn through the center
- skewed: not symmetric, shifted to one side or the other
What are two types of skewed graphs?
- negative skew: fewer scores at the low end, peak shifted to the right
- positive skew: fewer scores at the high end, peak shifted to the left
What is the mean of data?
- a.k.a. average
- a single value meant to typify a list of values
- most common measure of central tendency
- most appropriate when data are normally distributed (affected significantly by outliers or extreme values)
- symbolized as u (population data) or Xbar (for sample data)
- basic arithmetic mean calculated by adding up all data values and dividing by the number you have (e.g., 4+5+12 = 24/4 = 6 = mean)
What is kurtosis?
the sharpness of the peak of a frequency-distribution curve
Why is mean most appropriate for data that is normally distributed?
it is affected significantly by outliers or extreme values
How do you calculate the mean?
basic arithmetic mean calculated by adding up all data values and dividing by the number you have
e.g., 4+5+12 = 24/4 = 6 = mean
What is the median?
- midpoint of a distribution of scores so 1/2 fall above and 1/2 fall below (50th percentile)
- appropriate measure of central tendency with skewed distributions and those with outliers or extreme values
- if you have an odd array of values, put them in ascending order and the median is the humber in the middle
- if even array, put in ascending order, take mean of the two middle values