FANR 3000: TEST 1
61 Cards in this Set
| Front | Back |
|---|---|
|
closeness of a measured value to the true value
|
accuracy
|
|
closeness of 2 or more measurements to each other
|
precision
|
|
incorrect measurements due to carelessness
|
gross errors
|
|
errors of same size and magnitude
|
systematic errors
|
|
errors that are always present in measurement
|
random errors
|
|
linear version of cumulative histogram
|
ogive
|
|
display change in one variable in relation to another
|
line graph
|
|
similar to histogram but usually associated with categories
|
bar graph
|
|
circular graph showing how total quantitiy is distributed among group of categories
|
pie charts
|
|
Equation for outliers
|
Q1 - (1.5*IQR)
Q3 + (1.5*IQR)
|
|
measure of how spread out the data is
|
variance
|
|
square root of the variance
|
standard deviation
|
|
What is the empirical rule?
|
- 68% of data falls within 1 standard dev
- 95% of data falls within 2 standard dev
- 99.7% of data falls within 3 standard dev
|
|
value that represents how many standard deviations a value is from the mean
|
z score
|
|
how do you calculate standard error
|
Standard deviation divided by square root of n
(SD/sqrt(n))
|
|
What do these symbols stand for:
- Mu
- sigma
- sigma squared
|
- population mean
- population standard deviation
- population variance
|
|
What do these symbols stand for:
- N
- n
- x bar
|
- total number in population
- total number in sample
- sample mean
|
|
What do these symbols stand for:
- S of SD
- S squared
- sigma sub x bar
|
- sample standard deviation
- sample variance
- sample standard error
|
|
What do these symbols stand for:
- alpha
- v (nu)
|
- significance level in hypothesis test
- degrees of freedom
|
|
the most commonly observed value in the data set
|
mode
|
|
what is the range?
|
highest value - lowest value
|
|
A high variance would mean that the data will be ____
|
spread out
|
|
What is the formula for variance?
|
E(xi-xbar)2/(n-1)
|
|
What is the formula for standard error?
|
SD/sqrt(n)
|
|
What is the mean plus or minus the SD?
|
it is a descriptive statistic that shows how the observations within the sample differ from the sample mean
|
|
what is the mean plus or minus the standard error?
|
this is a description of the bound on the estimate of the population mean/how likely the sample mean is the population mean
|
|
set of all individuals possessing the particular attribute which we describe
|
population
|
|
values that summarize properties of the population
|
parameters
|
|
what are some common parameters
|
population mean (mu) and the population variance (sigma squared)
|
|
the portion or subset of the population that we actually count or measure
|
sample
|
|
what is a key assumption concerning the sample
|
the information obtained from the sample must reliably reflect the population
|
|
three types of samples
|
- simple random sample
- systematic sample
- stratified sample
|
|
taking a random sample of n units from a population of size N
|
simple random sample
|
|
sampling every kth unit from a population
|
systematic sample
|
|
dividing the population into non-overlapping blocks (strata) and taking a random sample within strata
|
stratified sample
|
|
the measurable characteristics of the samples of interest
|
variables
|
|
example variables
|
- age
- gender
- volume
- length
- density
|
|
two types or categories of variables
|
quantitative and qualitiative
|
|
Quantitative variables
|
numbers or data that can be measured
|
|
qualitative variables
|
words or data that can be observed but not really measured
|
|
two types of quantitative data
|
discrete - counts (integer values only)
continuous - measurement (any value withing a given range)
|
|
two types of qualitative data
|
Nominal - no natural ordering
Ordinal - have a natural order or rank
|
|
the set of measurements we have obtained
|
observations
|
|
Value which summarizes a property of the sample
|
statistic
|
|
You measure the height of a tree five times:
10.1, 10.0, 9.9, 10.1, and 10.0
The true height is 15.7
Is this low or high precision?
Is this low or high accuracy?
|
low accuracy and high precision
|
|
number of observations in each variable class
|
frequency
|
|
fraction of the total observations in each variable class
|
relative frequency
|
|
the frequency of a variable class plus the frequency of the classes below it
|
cumulative frequency
|
|
the relative frequencies plus the relative frequencies of the classes below it
|
cumulative relative frequency
|
|
bar graphs are similar to histograms but they are usually associated with _____ common with qualitative data
|
categories
|
|
used to display the change in one variable in relation to another
|
line graph
|
|
data is "distributed normally" if:
|
- distribution is symmetrical and bell shaped
- measures of central tendency are the same
- variable of interest has an infinite range
- the practical range is plus or minus 3 standard deviations above and below the mean
|
|
How many standard deviations is a score of 83 from the mean?
Mean is 87.5
SD = 3.75
|
(score - mean)/SD
(83 - 87.5)/3.75
= -1.2
|
|
What is the formula to find a z score
|
(x - xbar)/SD
|
|
Find probability that in any given year, more than 5000 acres will be burned? given mu = 4300 sd = 750
|
z score = (5000-4300)/750
z score = 0.93
(look up 0.93 in z score table)
= 0.3238
Greater than that is .5-.3238 =0.1762
|
|
equation for confidence interval
|
CI = xbar +- tn-1,a/2(SE)
|
|
what does the central limit theorem say?
|
regardless of the shape of the original distribution of data, the sampling distribution of the mean will be approximately normally distributed
|
|
What is a 90% confidence interval for a sample (n=26) of fish weights with a mean of 8.7lbs and a sample SE of 1.3lbs?
|
a = .10 (so a/2=.05)
df = 26-1 = 25
Look these up in t table = 1.7081
90% CI = 8.7 + or - 1.7081(1.3) =
8.7+ or - 2.22
|
|
Three things that impact the width of the confidence interval?
|
- confidence interval - as interval increases, it gets wider
- variability - populations with more variability generate wider CI's
- sample size - smaller samples sizes generate wider intervals
|
|
Steps for determining confidence interval
|
1. calculate mean of sample
2. calculate variance
3. determine critical t or z value
4. plug all those into CI formula
|
|
when would u use a critical z value or the z distribution table?
|
when the standard deviation of the population is known
|
FANR 3000: TEST 2