# Experimental design and analysis

5.0 / 5

HideShow resource information

- Created by: amy.louise
- Created on: 14-01-16 20:46

What is probability?

How likely an event will happen

1 of 119

How is probability expressed?

A number (P-value)

2 of 119

What is the maximum and minimum value probability can be?

0 and 1

3 of 119

What does the sum of probabilities for all outcomes equal to?

1

4 of 119

How can you calculate probability?

number of times an event happens / number of repeats

5 of 119

What does the null hypothesis state?

That there is no relationship between two measurements

6 of 119

What does a small p-value suggest?

That there is strong evidence that the null hypothesis is wrong

7 of 119

What does a large p-value suggest?

That there is strong evidence that the null hypothesis is correct

8 of 119

What would a p-value above 0.05 suggest about the difference?

Its due to chance

9 of 119

When are two events mutually exclusive?

When they can't occur at the same time

10 of 119

What is conditional probability?

The probability of event A occurring if event B has occured

11 of 119

What is the rule of subtraction?

Finding the probability of event A occurring by doing 1-(P A not occuring)

12 of 119

What is the rule of multiplication?

Finding the probability of both events A and B occurring. (pA x pB if A has occured)

13 of 119

What does statistical interference mean?

Drawing conclusions about an observation based on data

14 of 119

What is random sampling?

Sampling when the probability of including an individual from a population is the same for all individuals and is independent of other samples

15 of 119

What is bias sampling?

Sampling when the probability of an individual being picked to be sampled from a population is increased or decreased due to its characteristics

16 of 119

What is non-independant sampling?

Sampling when the probability of an individual being picked from a population to be sampled is dependant on other individuals from the population

17 of 119

What is a type I error?

When you reject a null hypothesis which is actually correct. You think theres statistical difference when there isn't

18 of 119

When are type I errors most commonly made?

When there is multiple testing

19 of 119

When would you use a bonferoni correction?

In order to reduce type I errors. When an experiment is testing many hypotheses

20 of 119

What does the bonferoni correction do?

Tests hypotheses to a certain statistical significance. 0.05 / no. of hypotheses

21 of 119

How does the bonferroni correction work?

Because the probability of getting at least one significant result increases as the number of hypotheses increases

22 of 119

What is a type I error also known as?

A false negative

23 of 119

What is a type II error?

When you accept the null hypothesis but its actually false. When you think theres no significant difference but there is

24 of 119

How can you reduce the chance of making a type II error?

Ensuring your test has enough statistical power

25 of 119

What is statistical error?

The likelihood that a study will detect an effect if there is a true difference to be seen

26 of 119

What is statistical error mainly effected by?

Same size and size of the effect

27 of 119

What is the effect size?

How big the effect of a variable had on samples

28 of 119

Does binomial distribution had a certain number of repeats?

Yes

29 of 119

What are the outcomes of a binomial experiment?

Success or failure

30 of 119

What is Q in a binomial experiment?

The probability of failure (1-P)

31 of 119

What is the binomial probability?

The probability that n-number of trials results in exactly X successes when the probability of a success is P

32 of 119

Does binomial distribution had a certain number of repeats?

No it has infinite trials

33 of 119

What has to be know in a poisson experiment?

The average number of successes that occurs within a specific region

34 of 119

What can a 'region' be in a poisson distribution?

Time, length, volume

35 of 119

What is the poisson probability?

The probability that exactly x successes will occur when there is a mean number of successes

36 of 119

Wha type of data do you use a chi-squared test for?

Nominal data that falls into particular categories

37 of 119

What does a one-factor chi-squared test do?

Compares expected values against observations of one variable

38 of 119

What does a two-factor chi-squared test do?

It tests two variables and identifies whether the factors are independent of each other

39 of 119

What is the null hypothesis in this test?

That there is no relationship

40 of 119

What is continuous data?

Data that has a unit and can be measured

41 of 119

What does the curve of normally distributed data depend on?

The mean and standard deviation from the mean

42 of 119

What doe the mean determine on the graph?

The location of the centre of the graph

43 of 119

What does the standard deviation determine?

The width and height of the graph

44 of 119

What is the total area under the graph equal to?

1

45 of 119

What % falls under 1 standard deviation of the mean?

68%

46 of 119

What % falls under 2 standard deviation of the mean?

95%

47 of 119

What % falls under 3 standard deviation of the mean?

99.7%

48 of 119

What does the Shapiro-wilk test for?

Normality of data

49 of 119

What does it allow you to see?

The distribution of your data

50 of 119

hIf the P-value is below 0.05 is the null hypothesis accepted/ rejected?

rejected

51 of 119

Is data normally distributed with a P-value of more than 0.05

Yes

52 of 119

What is the t-test used for?

To estimate the population parameters when the sample size is small or the population variance is unknown

53 of 119

What are parameters?

Numbers that summers data of a population. The mean and the standard deviation from the mean

54 of 119

Can a population distribution be directly calculated?

No, only estimated

55 of 119

What does the central limit theorem state?

That the sample mean of a statistic will follow a normal distribution as long as the sample size is large

56 of 119

If your sample size is small or you don't know the standard deviation of your population, what can you do?

Look at the distribution of the t-statistic

57 of 119

What does the standard error of the mean tell you?

It tells you how different the sample means are from the population mean

58 of 119

What is a confident interval?

A range of estimated values that will likely contain the population mean

59 of 119

What are confident limits?

The upper and lower boundaries of the confident interval

60 of 119

Is the standard deviation of large samples always the same?

Yes at 1.96. over 30 samples

61 of 119

What if you have a small sample size?

The standard deviations need to be adjusted

62 of 119

Is the standard deviation of a small sample size bigger or smaller than that of a big sample size?

Bigger

63 of 119

What is a t-value?

The difference between the standard deviation of the population and the sample.

64 of 119

What is a confidence level?

A percentage that tells you how many of the samples you can expect to include the true population mean within their confident intervals

65 of 119

What does a wide confidence interval suggest?

That you need a bigger sample size?

66 of 119

Is it good to have a narrow confidence interval and why?

Yes because it is more precise

67 of 119

How do you calculate variance?

Squared standard deviation

68 of 119

How do you calculate the confidence interval?

The sample mean + and - the standard error

69 of 119

What does a two-sample t-test measure?

It measures if themes of the two samples differer from the population mean and from each other

70 of 119

What is the test statistic of this test?

Z

71 of 119

When do you use ANOVA?

When you are comparing two or more variables

72 of 119

What are the assumptions of ANOVA?

The variance of all the errors are the same, The errors are independent and they are normally distributed

73 of 119

What does ANOVA test?

If the value of the variables differers significantly among 3 or more values

74 of 119

What do you need to calculate in ANOVA?

The grand mean and group mean

75 of 119

What is the F statistic ratio?

The between group variance / The within group variance

76 of 119

What effect does a higher between group variance have on F?

Increases it

77 of 119

What effect does a large amount of variance, due to chance, have on F?

Decreases it

78 of 119

What does a high F value suggest?

Moe significance and difference is not due to chance

79 of 119

How do you calculate sum of squares?

Data point - mean ^2

80 of 119

When do you use a Mann whitney U test?

When you're data is not normal and you are testing one variable

81 of 119

What parametric test is the Mann whitney U test compared to?

T-test

82 of 119

How do you display data for a Mann whitney U test?

Rank it in ascending order

83 of 119

Whats the next step?

You compare the two data points in each rank and find the difference. Ua and Ub

84 of 119

Are the differences separated between when the X column is bigger and then when the Y column is bigger?

Yes

85 of 119

What is the U value?

The ratio of Ua to Ub

86 of 119

when do you use a Kruskall wallis test?

When the assumption of ANOVA are not met. Data is not normally distributed and there are not equal variances

87 of 119

What is the null hypothesis?

The sample are from the same population

88 of 119

Does Kruskall wallis involve ranking data too?

Yes

89 of 119

What is the test statistic?

H

90 of 119

What is the kruskall wallis test used for?

When two factors are being tested

91 of 119

What is the limitation of the kruskall wallis test?

It only tells you that there is a difference or not between two groups. It doesn't tell you which groups

92 of 119

What does two-way ANOVA test?

It compares the mean difference between groups that have multiple factors

93 of 119

What types of variables must two-way ANOVA include?

Two nominal variables and one measurement variable

94 of 119

Wat do you test?

What effect each nominal variable has on the measurement variable

95 of 119

When would you transform data?

When it is not normally distributed

96 of 119

How do you transform data?

Apply a log transformation. Base 10 (log10)

97 of 119

Are you able to do statistical tests on transformed data?

Yes

98 of 119

What does a correlation (r) measure?

The extent to which two variables change together

99 of 119

What is the measurement of a correlation?

The correlation coefficient r

100 of 119

What does r range from?

-1 to +1

101 of 119

What would -1 and +1 tell you about the line?

Its a completely straight line where all points are on the line

102 of 119

What doe a correlation look for?

A linear effect

103 of 119

What unit does r have?

No units

104 of 119

How do you calculate a correlation?

Calculate the sum of squares for the Y and X values then calculate the sum of cross products by adding them together

105 of 119

What is r^2?

A coefficient of determination

106 of 119

How many samples does a test need t give a significant r?

3

107 of 119

What is regression?

It calculates the 'best' straight line through the plots in order to express the relationship of the correlation coefficient

108 of 119

What is the regression line?

A line that minimises the sum of squared deviation of the plots from the line

109 of 119

What is the intercept symbolised as?

c

110 of 119

What is the intercept?

The point at which the line crosses the x-axis

111 of 119

What is the slope symbolised as?

B

112 of 119

What is the slope?

The gradient of the line

113 of 119

How do you calculate the intercept?

The mean of Y - (mean X x b)

114 of 119

What statistical test do you use to test the significance of regression?

Pearsons correlation

115 of 119

Can you use not normally distributed data in regression?

No you must first transform the data

116 of 119

What do yu do if the data does show relationship but its not linear?

Use a spearmint rank correlation test

117 of 119

What type of data is linear models used on?

Normal data

118 of 119

What type of data is generalised linear models used on?

Non-normal data/ count data

119 of 119

## Other cards in this set

### Card 2

#### Front

How is probability expressed?

#### Back

A number (P-value)

### Card 3

#### Front

What is the maximum and minimum value probability can be?

#### Back

### Card 4

#### Front

What does the sum of probabilities for all outcomes equal to?

#### Back

### Card 5

#### Front

How can you calculate probability?

#### Back

## Similar Biology resources:

5.0 / 5

2.0 / 5

0.0 / 5

0.0 / 5

1.5 / 5

0.0 / 5

5.0 / 5

Teacher recommended

## Comments

No comments have yet been made