Statistics

Question 1

what are stats tests used for

Answer 1

to determine whether differences between data sets are significant or if it is due to natural variation.

Question 2

how do u plot the data u collect in stats

Answer 2

in a normal distribution curve

Question 3

what is the mean

Answer 3

the average value and it is the maximum height of the normal distribution graph

Question 4

what is the standard deviation

Answer 4

the spread about the mean

Question 5

to what confidence/percentage do biologists use for the s.d.

Answer 5

95% = 1.96 s.d.
95% of pop lie within this value

Question 6

how can u use a graph to visually see the variation

Answer 6

if the curve is wide then it means there is a lot of variation in the sample

if the curve is quite narrow there is not much variation

Question 7

in a normal distribution, what is the percentage of the pop that lies within one s.d. above pr below the mean

Answer 7

68%

Question 8

how much of the pop lies within 2 s.d. above or below the mean

Answer 8

95%

Question 9

how is standard deviation a better way to measure the spread than the range

Answer 9

it is less affected by extreme values

Question 10

how can standard deviation values be used to plot error bars

Answer 10

plot one standard deviation above the point an one below so that the total length of the bar is 2 standard deviations

Question 11

how to work out s.d on calculator

Answer 11

press mode
then press 2
press 1 ad go on table
put in values
press AC
shidt then no 1
no. 4
and then no. 4

Question 12

which eq should u always use for bio

Answer 12

use the sample one = n-1

Question 13

example calc - mean IQ is 100 with s.d. 15
a) bwt what IQ’s do 95% fall

b) what proportion have IQ over 130

Answer 13

mean = 100
s.d. = 15
95% lie with +/- 2 s.d.
95% of pop 100 +/- (2x15)
IQ range 70 —-> 130

b) 2.5%

Question 14

what is a working hypothesis

Answer 14

idea of what you think might happen

Question 15

what is a null hypothesis

Answer 15

what you think will not happen

Question 16

What should u make sure that u do before starting analysis

Answer 16

write down null hypothesis

Question 17

what probalilty do u work with

Answer 17

0.05 probability level = P=0.05

Question 18

what results of stats are we looking for

Answer 18

95% chance it is significant and not due to chance
or 95% that result was due to chance

Question 19

what test do u use if u need to compare two sets of data when u have 30 values in each data set and the data is normally distrubuted

Answer 19

the t-test

Question 20

what does the t-test find

Answer 20

wether the difference between the means is significant

Question 21

what are the two types of t-test

Answer 21

unpaired
paired

Question 22

what is an unpaired t-test

Answer 22

used for comparing the means from two groups of different individuals eg the height of limpets in two different habitats

Question 23

what is the paired t-test

Answer 23

this is used when the data is from the same individuals eg measurement taken from the same people before and after a drug test

Question 24

will the t value be larger or smaller if the results are significant

Answer 24

larger

Question 25

will the t value be larger or smaller if the results are not significant

Answer 25

smaller

Question 26

how to carry out an unpaired t-Test

Answer 26

-start with null hypothesis - there is no significant difference between the means no of …
-calculate the mean for each data set
-calculate the standard deviation for each data set using the formula/ calculator
-put the mean and standard deviation values into the t-Test formula to calculate t value
-calculate the degrees of freedom
-look up critical value at P=0.05 and compare with calculated p value
-conclusion

Question 27

what is the degree of freedom

Answer 27

number of samples - 1

Question 28

what is the conclusion if the tcalc >/ tcrit

Answer 28

-null hypothesis is rejected
- there is a significant difference between the two mean values
-with less than a 5% probability of the results being due to chance

Question 29

what is the conclusion if the tcalc /< tcrit

Answer 29

-the null hypothesis is accepted
-there is no significant difference between the two mean values
-there is a 95% probability of results being due to chance

Question 30

what is the spearmans rank correlation coefficent

Answer 30

used to look for associations between different measurements from the same sample
-use to test the strength and direction of the correlation

Question 31

how to set up spearmans rank

Answer 31

-set up a table
-place the values from each site into columns
-rank each - the most being 1
-is there are two values add next two ranks together and divide by 2
-minus the two ranks from each other -A-B
-square this value
-add these tg
-sub into eq
1- (6x sum of D2/ n^3 x n)

Question 32

next steps after calc spearmans rank

Answer 32

find on critical value of coefficent
interpret stats
calc is bigger then reject null - sig correlation
crit bigger then accept nul - no sig correlation

Question 33

what is the chi-squared test

Answer 33

looking at frequencies of individuals in different categories - difference bwt predicted and observed is significant

Question 34

what are chi-squared tests often used

Answer 34

genetic crosses

Question 35

what is the chi-squared formula

Answer 35

sum of (O-E)^2/ E

Question 36

how to set up chi-sqaured table

Answer 36

obsereved no and total
expected no and total
O-E
(O-E)^2
(O-E)^2/E and then total

Question 37

how to find expected values

Answer 37

divide total of observed by no of locations

Question 38

how to find expected values for more complicated chi-squared

Answer 38

times total of site 1 by total column over pverall total

Question 39

chi-sqaured step 2

Answer 39

find degrees of freedom
for compliacted ones - ( number of rows-1 ) x (number of columns -1 )
then find critcal values
and use same conclusion for others