lecture 1 variables + CI Flashcards
independent variable
Experimental or predictor variable
Can be manipulated in an experiment
Changed to have an effect on a dependent variable
dependent variable
Outcome variable
waht is the independent and dependent variable:
study being done to determine efficacy of new analgesic at different doses
Independent variable: dose of medication
Dependent variable: change in pain scale
Nominal variable
categorical outcomes with MORE than two possible outcomes; not numeric
- categories in NAME only, w no particular order
i. e. blood types A, B, AB, O - -> there can be a mode but nO mean (avg b/t type A & B)
Binomial (dichotomous) variable
categorical outcomes with TWO distinct possible outcomes
- subset of nominal
i. e gender (yes/no)
Ordinal variable
express rank and order matters (though not the exact value) (pain scale, level of education, restaurant ratings 1-5 stars)
Continuous variable
represent data capable of possessing any value in a given range (BP, temperature, weight)
- NUMBER
i. e. BP 110 to 120 is the same as 120 to 130–> 10 pt difference
Interval variable
continuous spaced with equal intervals or distances; the zero point is not considered meaningful (example: IQ or temperature)
-diff b/w 5F and 4F is same as 60F to 59F
-0 degrees does not mean NO temperature, it can go lower **
when you change the scale in the y axis (starts at 0 then change scale to 25) does it mean results are different?
no. it’s a matter of how data is represented, makes it look different but not
Ratio variables
cant go below zero
difference between interval and ratio
ratio can be calculated bc 0 point DOES matter
mean
the average
- add all values and divide by total
median
middle value
- put in order
is the median influenced by the outliers
negative
is the mean sensitive to outliers
yessss. –> mean wont be very representative
- it skews the result
what does “n” mean in a study
number of observatiions
what is the percentile of median
50%
if the mean is very similar to the median…. this means….
not a lot of outliers
trimmed mean
ignoring the highest and lowest (usually a percentage)
–removing influence of outliers*
mode
value that occurs most commonly in data set
- not useful w continuous variables
- does not always assess the center of a distribution
does the mode assess the center of a distribution
no
error
variability in the data
most of the scatter in biologic and clinical studies is due too…
biologic variation
i.e. aging, diet, mood
bias
anything that skews the data one way or another
-influence study
where do biased measurements result from
systemic errors
what helps to eliminate error in regards to population size?
a larger population = less chance for error
- cancel each other out
- helps to tighten around mean/median
what does a wide box represent in a box and whisker plot
the wider the box in 25th and 75th percentile the more variability the error is
- seen in smaller samples
histogram is also known as
frequency distribution plotted as a bar graph
how do you get the total number of values in a histogram?
you add the height of the bars
standard deviation define
the variation among values expressed in the same units as the data
- spread of data around the mean/distribution
the larger the SD means…
the more spread out the distribution of data about the mean
data plotted on a frequency distribution tends to result in a….
SYMMETRICAL bell shaped curve
what is another name for bell shaped curve
Gaussian distribution
where do many of the values end up in the bell shape distribution?
near the center of the mean
–few values end up farther away
vertical vs horizontal axis in the Gaussian Distribution curve
horizontal: various values that can be observed
vertical: frequency
what is the relationship between the mean and median in a Gaussian Distribution curve?
they are both the SAME; distribution is symmetrical
what does the area under the Gaussian curve represent
the entire population
what is considered a standard normal curve
when the mean equals 0 and the SD equals 1.0 –> 68%
define variable “z”
the number of SD away from the mean
the “normal” distribution ____ define normal limits
does NOT
standard error of the mean (SEM)
the ratio of the SD dividied by the square root of the sample size
SEM does NOT directly quantify ____ or ____
scatter or variability
the ___ the sample size, the smaller the value of the SEM
larger
not a measure of the spread of the data,, but rather how well you know the population mean ….
SEM
SEM is always ___ than SD
smaller
what does a small SEM suggest?
that the sample mean is close to the population mean
-large sample size
the SEM can be used to construct _______ around a sample mean
confidence intervals
what values determine the Confidence Interval of a Mean
- sample mean
- SD
- sample size
- degree of confidence
confidence interval of a mean is centered around —-?
sample mean
width of the confidence interval is ____ to the sample SD
proportional
what needs to be assumed in order to interpret CI of a mean?
- random sample
- independent observations (cant be measured twice)
- accurate data
- assessing an event you really care about
- the population is distributed in a gaussian manner
