scientific method: stats

Question 1

what is the standard deviation (S)

Answer 1

a measure of how far apart
numbers are in your sample/ is a number that indicates how far are
the values from the mean on average in the same scale as the measure

Question 1

what is the variance (S^2)

Answer 1

describes the relative distance
between the data points & the
mean

Question 2

what is the advantage of Stan dev

Answer 2

in in the same units as the data, the variance is the unit^2

Question 3

how is the variance calculated

Answer 3

SUM (observations – average)^2
/ number of observations - 1

Question 4

how is the stan dev calculated

Answer 4

sqare root of the variance (sqrt S^2 = S)

Question 5

what is standard error

Answer 5

measure of the sampling error

Question 6

what does a higher SE , SD, S mean ?

Answer 6

• generally indicates higher variability/more outliers.
• If data points are farther apart (higher S/SD) you can be less certain that the mean represents the true
  average of the sample.
• Higher SE similarly implies that you can be less certain that the sample mean accurately represents that of the population.

Question 7

on graphs, should the value of the error bar (SE) be included?

Answer 7

No, do not write the value, only put the error bar

Question 8

what is the nul hypothesis ?

Answer 8

STATUS QUO
– this is the hypothesis you are testing with stats
– It is always the status quo (i.e. there will be no difference)
and the opposite of the alternate hypothesis
– It depends on the goal of your experiment

Question 9

what is the alternate hypothesis?

Answer 9

tests your PREDICTION
– this is the opposite of the null hypothesis

Question 10

what is a directional hypothesis

Answer 10

• indicated direction of the change, more, less
• is 1 tailed (important for t crit)

Question 11

what is a non-directional hypothesis?

Answer 11

• Indicates that there will be a change, but not what
• is 2 tailed

Question 12

What does it mean when error bars overlap in a graph

Answer 12

always means that is NOT statistically significant

Question 13

what does it mean if the sample size is more then 10, the gap is more then 2, and P value is smaller then 0.05

Answer 13

Significant

Question 14

what does it mean if the sample size is more then 10, the gap is 2, and P value is smaller then 0.05 (about 0.01)

Answer 14

significant

Question 15

what does it mean if the sample size is more then 10, the gap is 1, and P value is about 0.05

Answer 15

likely significant

Question 16

what does it mean if the sample size is less or equal to then 10, the gap is more then 2, and P value is smaller then 0.05

Answer 16

significant

Question 17

what does it mean if the sample size is less or equal to then 10, the gap is 2, and P value is about 0.05

Answer 17

likely significant

Question 18

what does it mean if the sample size is less or equal to then 10, the gap is 1, and P value is bigger then 0.05

Answer 18

not significant

Question 19

what are examples of control variables

Answer 19

animals attracted to soil, bacteria that will form, seed variability, pH of soil, distance between seeds, health of the seeds, size of the pot

Question 20

what are examples of limitations

Answer 20

• has not been tried on other species
• only conducted in those conditions (inside, outside)
• different pH might have different effext
• animals can be attracted to the plant if its outside
• might not work with big sample size
• genetic variability
• nutrient availabilty in another environment
• effects of container (size, type, drainage)
• pH of soil

Question 21

when should you not use an independent T test

Answer 21

• when all data is from same individuel (before and after)—– this would be a paired T-test
• when there are less or more then 2 groups
• when there are no averages

Question 22

what are degrees of freedom

Answer 22

opportunities of change