BIO 330 Flashcards
sampling error imposes
imprecision (accuracy intact)
caused by chance
sampling bias imposes
inaccuracy (precision intact)
accurate sample
unbiased
precise sample
low sampling error
good sample
accurate
precise
random
large
2 types of data
numerical
categorical
numerical data
continuous
discrete
categorical data
nominal
ordinal
types of variable
response
explanatory
response variable
dependent
outcome
Y
explanatory variable
independent
predictor
x
subsamples treated as true replicate
pseudoreplication
subsamples are useful for
increasing precision of estimate for individual samples (multiple samples from same site averaged)
contingency table
explanatory- columns
response- rows
totals of columns and rows
2 data descriptions
central tendency
width
central tendency
mean
median
mode
width (spread)
range standard deviation variance coefficient of variation IQR
effect of outliers on mean
shifts mean towards outliers- sensitive to extremes
median doesn’t shift
sample variance s^2 =
sum( Y_i - Ybar )^2 / n-1
coefficient of variation CV =
100% ( s / Ybar )
high CV
more variability
skewed box plot
left skewed- more data in ‘bottom’- first quartile
right skewed- more data in ‘top’- 3rd quartile
when/why random sample
uniform study area
removes bias in sample selection
when/why systematic sample
detect patterns along gradient- fixed intervals along transect/belt