Statistics

Question 1

what is a null hypothesis? what is an alternative hypothesis?

Answer 1

null: independent variable had no effect on dependent variable

alternative: independent variable had an effect on dependent variable

Question 2

what is p value?

Answer 2

• probability value
• probability that the NULL hypothesis is supported
• low p-valie = indep prob has effect on dep

alpha = 0.05 –> critical value

Question 3

what is degrees of freedom?

Answer 3

number of samples - 1

Question 4

what is a continuous variable?

Answer 4

• quantitative value (any value between 0 and infinity)
• event count data (whole numbers)

ex. height, number of leaves

Question 5

what is a categorical variable?

Answer 5

• limited number of fixed value

ex. assign 3 diff temperatures

Question 6

if the dependent variable is continuous and the dependent variable is continuous, what statistical test would you perform?

Answer 6

correlation test
- pearson correlation coefficient, n value (sample size), and p -value

Question 7

how would you present data in a correlation test?

Answer 7

• line/scatter plot

error bars possible around point on statter plot

Question 8

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what is the difference between regression and correlation?

Answer 8

• correlation: unsure if variable has an effect on other variable
• regression: expectation that one variable has an effect on the other

Question 9

what is the multiple R value?

Answer 9

pearson correlation coefficient

Question 10

if the dependent variable is continuous and the independent variable is categorical woth 2 treatments, what statistical test would you perform?

Answer 10

t-test
- t-test value, degrees of freedom, p value

ex wet vs dry, cold vs hot, two locations

Question 11

how would you represent data if indep vairable is categorical with 2 treatments?

Answer 11

bar graph of mean values of each treatment with 2 columns and error bars

Question 12

what are standard error vs deviation? difference?

Answer 12

• measurements of amount of variation in a sample

deviation: how spread out the data are in the dataset

error: estimate of how precise the mean estimate is

Question 13

calculating standard error?

Answer 13

standard deviation / square root of number of samples

standard error < standard deviation

Question 14

when to use standard deviation?

Answer 14

describing how variable the data in a dataset are

Question 15

when to use standard error?

Answer 15

when quantifying the uncertainty around an estimate of the mean

standard error bars overlap = no difference between means

no overlap = treatment is significantly different for each other

Question 16

what is t-test paired vs t-test two sample?

Answer 16

paired: same individuals under both conditions
two sample: different individuals for each treatment

use + value for t statistic

Question 17

if the dependent variable is continuous and the independent variable is categorical with more than 2 treatments, what statistical test would you perform?

Answer 17

ANOVA
F-stat, first df, second df, p value
1st df: # groups/treatments -1
2nd df: > 1st df

Question 18

how would you represent data if indep vairable is categorical with more than 2 treatments?

Answer 18

bar graph of means of each treatment with error bars (standard error)

Question 19

what is a characteristic of ANOVA/having multiple categorical indep variables?

Answer 19

significant difference among treatments, but we don’t know which treatments have the same effect and which onces are different

to determine this we do a POST-HOC test = multiple t-tests

Question 20

what does a post-hoc test do? how do you do it?

Answer 20

tells you which treatments are different from each other/have different effects on dep variable

do as many t-tests as the number of comparisons to equal post-hoc test

Question 21

how do you analyze and report post hoc test data? how is the results represented on the graph?

Answer 21

analyze:
- compare each t test to corrected alpha/critical value; low p value = sig difference between treatments;
- if sig diff, assign diff letters; if no sig diff, assign same letter
- this is seen on graph bc no sig diff = error bars overlap

report:
- say if sig diff and say p value and say which group had higher value

Question 22

what happens to alpha/critical value in post-hoc test? why do we do this?

Answer 22

alpha value/# comparisons(# tests done between each of the treatments)

more tests = increase likely hood that p-value is less than 0.o5 by chance

test ex. 4 treatments = A+B, A+C, A+D, B+C, B+B, C+D = 6 tests

Question 23

what is included in fig caption?

Answer 23

indep, dep variables, SE, short interpretation of result (sometimes)

Question 24

where does legend appear in relation to table?

Answer 24

above table