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Biology Practicals > Statistical Tests > Flashcards

Statistical Tests Flashcards

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1
Q

What is a control groups

A

A separate group you set up within your experiment where you treat them exactly the same without applying the independent variable

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2
Q

What do you always say when asked how something acts as a control group

A

“ to compare to “ “to show the effect of…. Then name the indépendant variable “

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3
Q

What should you say when it asks to describe how a control group should be treated

A

It should be treated with exactly the same conditions as the experimental group
Apart from the indépendant variable shouldn’t be applied to this group

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4
Q

What do you say if the experimental group are being given a tablet or injection of a drug

A

The control group should be given an injection or tablet as well just without the drug

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5
Q

What should you say if it asked to suggest what the control should be in the experiment

A

If the experiment involved liquid then the control normally involves using water
If the experiment involved using enzymes the control is normally no enzymes or a boiled enzymes.

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6
Q

What should you say if asked to explain why you use a control group or explain how group x acts as a control

A

Group X allows you to compare to group y so you can see the effect of (independant variable)
This is to ensure that no other factor is having an effect on the data

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7
Q

What can sometimes happen however

A

Control groups can sometimes show the effect of more than one factor
It’ll be worth 2 marks and you need to mention both of these factors

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8
Q

What is the common level of probability used in biology

A

5% written as p= 0.05

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9
Q

What happens if you calculated value is equal to or greater than the critical value for p= 0.05

A

There is a significant different between X and Y
There is a less than 5% probability than the different js due to chance
Reject the null hypothesis
There is likely to be a biological cause behind the difference

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10
Q

What happens if you calculated value is less than the critical value for p=0.05

A

There isn’t a significant different between X and Y
There is a greater than 5% probability that the different is due to chance
Accept the null hypothesis
Cannot be confident of a biological cause

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11
Q

What happens if you are given a P value in the question

A

They have already carried out the stats test and you need to conclude without comparing this number to a critical value

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12
Q

What happens if you are given the number 0.05

A

Say 5% in your answer
If you were given 0.02 then say 2% if it were 0.001 it’s 0.1%

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13
Q

What about the signs

A

If it is P= 0.05 then the probability the difference is due to chance IS 5%
If it’s P< 0.05 then it’s LESS THAN 5%
If it’s P> 0.05 then it’s MORE THAN 5%

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14
Q

When do you use the Chi squared test

A

To compare frequencies in different catagories or comparing expected and observed frequencies in catagories

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15
Q

What is the formula for X2

A

(See in booklet)

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16
Q

What would be the expected numbers if you want to collect earthworms from field A and B

A

Do the average so if field A is 167 and field b is 198 do 167+198/2 which is 182.5

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17
Q

What are the observed values in that experiment

A

167 and 198

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18
Q

In the chi squared table what should you fill in

A

O value
E vakue
(O-E)
(O-E)2
(O-E)2
Divided by E

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19
Q

What is the weird symbol thingy value

A

You add up the last column of numbers

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20
Q

What is the degrees of freedom

A

The number of catagories - 1 so for example
2-1

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21
Q

What is the critical value

A

For 1 degree of freedom the critical value is 3.841
2 degrees it is 5.991
3 degrees is 7.815
4 degrees is 9.488
5 degrees is 11.071

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22
Q

What happens if the calculated value ( 2.64 is less than 3.841) Is the less than the critical value

A

the null
There is no significant difference
There is less than a 5 % probability the difference is due to chance

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23
Q

What null hypothesis do you write for the chi squared test

A

There is no difference in the number of (dependant variable) between group 1, group 2 etc

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24
Q

What is the null hypothesis for the correlation coefficient

A

There is no correlation between (variable 1 ) and variable 2

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25
Q

When do you use the correlation coefficient

A

When looking for a correlation between 2 variables
(Normally represented as a scatter graph or line graph)

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26
Q

What is the method for the correlation coefficient

A

It’s suitable for data that can be ranked from highest to lowest
1) rank each set of data (highest number is 1 next highest is 2 etc)
2) if you have 2 or more pieces of data that are the same number give one a rank eg 5 and one 6 then average it
3) find the difference between 2 ranks for each pair of values
4) square the difference
5) total the square of the differences

27
Q

What is the equation for the correlation coefficient

A

See in booklet

28
Q

What does each number mean

A

rs- speareman rank correlation coefficient
n- number of pairs of items in the sample (10)
D- difference between each pair of ranked measurements
Substitute numbers into the formula

29
Q

What does the value for the speareman rank do

A

It always lies between +1 and -1
So if it is near to +1 it has a positive correlation if it is close to 0 it has no correlation if it is close to -1 it has a negative correlation

30
Q

What conclusion can you make

A

As pH increase heights of buttercups decreases if it’s negative
As pH increase heights of buttercups increases if it me positivr

31
Q

What would the critical value be

A

If 5 measurements then it’s 1
6= 0.89
7=0.79
8=0.74
9=0.68
10=0.65

32
Q

When do you use a Chi squared test

A

Used to compare frequencies of organisms to see whether or not the number of organisms in one catagory is significantly different in another catagory

33
Q

What is the formula for the Chi squared test

A

The sum of the observed minus expected value squared divided by expected

34
Q

How do you work out the expected value

A

the average between the thingies

35
Q

What happens if the value is less than the critical value

A

Accept the null
Theresno significant difference
Theres more than a 5% probability that the difference is due to chance

36
Q

What happens if the value is more than the critical value

A

Reject the null
There is a significant difference
Less than 5% probability the difference is due to chance

37
Q

When do you use the students T test

A

When comparing 2 means

38
Q

What is the formula for the students T test

A

Mean of sample 1 - mean of sample 2
divided by
SD of sample 1/No of sample for sample 1 add SD of sample 2/No of sample for sample 2

39
Q

What is the method for the Students T test

A

1) First calculate the mean and standard deviation of each sample
2) Enter numbers into the equation
3) Calculate how many degrees of freedom you have using the calculation n1-1 + n2-1

40
Q

What is the uncertainty of an instrument

A

Half the smallest resolution. For example a thermometer is likely to have an uncertainty of +/- 0.5 if the graduation is 1 celsius apart

41
Q

What is the equation for percentage uncertainty

A

uncertainty divided by reading times by 100

42
Q

What do you do when combining uncertainties

A

You must work out the uncertainties of each separate first then add them together

43
Q

How do we reduce uncertainty

A

Choosing instruments withmore graduations at smaller intervals or higher resolutions
Repeating the reading

44
Q

What is standard deviation

A

A measure of how psread out your repeats are from your mean

45
Q

What are the advantages of using the SD instead of the range

A

It shows the spread of data around the mean whereas the range is only the difference between the highest and lowest value
Reduces the effect of anomalies but the range includes anomalies
can be used to indicate whether a difference between results is significant

46
Q

How would you describe which statistical test to use

A

1) Say to write a null hypothesis
2) State which test to use and say to calcualte its test statistic
3) Look up in table to find the critical value of p=0.05
4) Use the figure to accept or reject the null

47
Q

With correlations can you conclude anything

A

No because correlation does not equal a casual relationship as it may be due to another factor ( common 2 marker)

48
Q

How do you answer “ Explain what the results of the statistical test shows”

A

1) state if the difference in distribution is due to chance or not for any species
2) State why (p>0.0001 which is highly significant)

49
Q

Why is it useful to express results in ratio form

A

It allows for comparision as the masses/volumes/populations are different

50
Q

What should ratios be displayed in the form of in biology

A

_____:1

51
Q

How would you calculate the ratio

A

Divide the first number in the question by the second number

52
Q

How do you calculate percentage change

A

Final value- initial value divided by initial value x 100

53
Q

How do you draw a tangent to find the rate of reaction

A

Find the point of the graph where you need to know the rate
Angle the ruler so that there is equal space between the ruler and curve
Draw a line between the ruler using a sharp pencil

54
Q

How do you calculate the pH of a solution

A

-log10(H+)

55
Q

How do you calcualte specific heat capacity

A

Mass x Specific heat capacity x temperature change

56
Q

What are the conversions from micrometres, millimetres and nanometres

A

mm-nm=x10^6
nm-mm=divide 10^6
mm to micro- x1000
nano to micro- divide by 1000
milli to micro - x1000
micro to milli - divide by 1000

57
Q

What is the equation for magnification

A

Image length divided by actual length

58
Q

How do you calculate the length of a certain stage of mitosis

A

Number of cells in a certain stage divided by total number of cells
x100

59
Q

How do you calcualte mitotic index

A

number of cells undergoing mitosis
divided by total number of cells

60
Q

What do you always say when asked to suggest 2 factors to consider

A

Ethical considerations
Larger number of sample to increase reliability

61
Q

How do you identify the concentration of an unknown solution of glucose

A

You use to formula
C1 x V1= C2 X V2

62
Q

How do you plot a calibration curve using a colorimeter for a substance other than glucose

A

1) Make a dilution series of known concentrations of ( name the substance you are identifying )
2) Use a colorimeter to measure the absorbance of each concentration
3)Plot a graph of concentration on the x axis and absorbance on the y axis and draw a calibration curve
4) Use the absorbamce of the sample to find the concentration from the calibration curve

63
Q
A

Biology Practicals (3 decks)

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