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HSPH > Interpreting Data > Flashcards

Interpreting Data Flashcards

1
Q

How do you calculate standard deviation?

A

Take the mean - Distance from the mean, squared

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2
Q

When would using the median result be more appropriate? [1]

A

Better to use median when have a skewed distribution, can avoid the influence of outliers

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3
Q

When would you use IQR vs STD? [1]

A

When wide outliers / skewed distribution: Better to use IQR in this case, to avoid the influence of outliers

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4
Q
A
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5
Q
A
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6
Q

What value is changing between the different colours in this Gaussain Distribution?

A

mean value

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7
Q

What value is changing between the different colours in this Gaussain Distribution?

A

Standard deviation

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8
Q

What is the standard deviation measuring? [1]

A

It is essentially calculating the average distance from the mean, and therefore the measure of spread of the results you have obtained. This is shown visually on the image here.

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9
Q

What are the references ranges are for 95%, 99% and 90% range for STD?

learn

A
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10
Q

What are the references ranges are for 95%, 99% and 90% range for STD?

learn

A

99% range (0.5th to 99.5th centile) = mean ± 2.58 SDs

95% range (2.5th to 97.5th centile) = mean ± 1.96 SDs

90% range (5th to 95th centile) = mean ± 1.64 SDs

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11
Q

Repeated sampling from a population

If the sample size isn’t too small then the distribution of the sample mean will be []

A

If the sample size isn’t too small then the distribution of the sample mean will be Gaussian

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12
Q

What is the STD of Gaussian distribution called? [1]

A

standard error

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13
Q

How do you calculate standard error of the mean? [1]

A
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14
Q

What would the standard error of the following be?

n=163
mean=22
standard deviation=4

A
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15
Q

How do you calculate the 95% confidence interval (CI) of a sample mean?

A

95% CI = sample mean ± 1.96 × standard error

key !!

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16
Q

What do the results from condfidence interval for the mean mean?

E.g. if 21.4-22.6

A

If results is 21.4 0 226:

We would expect 95% of samples of the same size to have a mean BMI between 21.4 and 22.6

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17
Q

95% confidence interval

Which is the correct definition?

In the population we are 95% sure that the mean weight could be as low as 75kg or as high as 81kg

In this study 95% of men weighed between 75kg and 81kg

A

Which is the correct definition?

In the population we are 95% sure that the mean weight could be as low as 75kg or as high as 81kg

In this study 95% of men weighed between 75kg and 81kg

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18
Q

What is the difference between reference range and CI? [1]

A

The reference range is defined as the interval between which 95% of values of a reference population fall into, in such a way that 2.5% will be below and 2.5% will be above.

Confidence interval is more concerned with the idea that the mean could be as low as/high as the two values given.

19
Q

What is difference in values used to calculate STD and SE? [2]

A

Use standard deviation for ranges (for individual values)

Use standard error for confidence intervals (for means)

20
Q

What is correlation (pearson) score for the following?

A

Perfect positive correlation: r=1

Perfect negative correlation r=-1

No correlation = r=0

21
Q

If the data do not follow a Gaussian distribution or there is a non-linear monotonic relationship [] correlation can be used

A

If the data do not follow a Gaussian distribution or there is a non-linear monotonic relationship Spearman’s rank correlation can be used

22
Q

x

A
23
Q

Pearson’s correlation and linear regression describe which type of associations? [1]

A

Pearson’s correlation and linear regression only describe linear associations

24
Q

Different regression curves can be fitted where the data pattern is

What type of regression modal would you use for the following?

A

Polynomial – quadratic (y=b0+b1x+b2x2)

25
Q

Different regression curves can be fitted where the data pattern is

What type of regression modal would you use for the following?

A

Polynomial – quadratic (y=b0+b1x+b2x2), cubic (y=b0+b1x+b2x2+b3x3) etc

26
Q

Different regression curves can be fitted where the data pattern is

What type of regression modal would you use for the following?

A

Exponential growth (y=bx;b>1)

27
Q

Different regression curves can be fitted where the data pattern is

What type of regression modal would you use for the following?

A

exponential decay (y=bx;b<1)

28
Q

Different regression curves can be fitted where the data pattern is

What type of regression modal would you use for the following?

A

Sigmoid

29
Q

Multivariate linear regression

State if is dependent or independent on variables

A
30
Q

What is meant by degrees of freedom? [1]

How do you calculate degress of freedom? [1]

e.g In the example we have 150 girls and 156 boys, what is the degrees of freedom? [1]

A

These are the number of values that are free to vary

In the example we have 150 girls and 156 boys, so there are 149+155=304 degrees of freedom.

31
Q

If the 95% CI for a difference excludes 0 then p []?

If the 95% CI for a difference includes 0 then p []?

A

If the 95% CI for a difference excludes 0 then p < 0.05

If the 95% CI for a difference includes 0 then p ≥ 0.05

32
Q

In a study, a group of patients took statins and another group placebo. The mean difference in LDL cholesterol was 1 mmol/L:

The 95% CI was 0.2 to 1.8
The 99% CI was -0.1 to 2.1

Which is correct?
P-value is less than 0.01
P-value is less than 0.05 but greater than 0.01
P-value is greater than 0.05

A

In a study, a group of patients took statins and another group placebo. The mean difference in LDL cholesterol was 1 mmol/L:

The 95% CI was 0.2 to 1.8
The 99% CI was -0.1 to 2.1

Which is correct?
P-value is less than 0.01
P-value is less than 0.05 but greater than 0.01
P-value is greater than 0.05

33
Q

What analysis could you use where two measurements are made on the same group of people? [1]

A

Paired t-test:

Calculate individual differences – is the mean of those different to 0?

34
Q

T-tests assume data follows a Gaussian distribution.

If the data doesn’t follow Gaussain distribution what tests would you perform if:

Instead of 2-sample t-test? [1]

Instead of paired t-test? [1]

A

Instead of 2-sample t-test do Mann Whitney U-test (Wilcoxon rank sum test)

Instead of paired t-test do Wilcoxon signed rank test

35
Q

For example, in the free thyroxine samples in pregnant women shown above, the mean is 14 and the standard deviation is 1.7. Calculate the 95% reference range [1]

A

The 95% reference range is 14 +/- 1.96x1.7 = 10.7 to 17.3.

The observed middle 95% of women in this sample is 10.9-17.5. This therefore means 2.5% of women in the sample had a level of thyroxine less than 10.9 and 2.5% had a level of thyroxine greater than 17.5.

36
Q

What is linear regression used for? [1]

A

usedto predict the value of a variable based on the value of another variable.

37
Q

How do you calculate linear regression?

A

Y = a + bx.

Y = outcome (dependent variable)

Measured/affected during experiment

X = predictor (independent variable).

Factor changed during experiment.

B = slope (Y2-Y1/X2-X1).

A = intercept.

NOTE: this only works for linear associations.

38
Q

How would you interpret this linear regression? [1]

A

UPDRS decreases by 0.7 for every unit increase in kinesia score

39
Q

How would you interpret this linear regression? [1]

A

UPDRS decreases by 0.7 for every unit increase in kinesia score

40
Q

How can toy adapt linear regression to for multiple factors? [1]

A

Independent variables can be continuous, categorical or a mix

Example: kinesia score according to age and sex

41
Q
A

B

What is being predicted should always be on the vertical axis

42
Q

What do you use a T-test and chi-squared test for? [2]

A

T-test cans be done for comparing continuous variables

Chi-squared test for comparing categorical variables

43
Q

What is the link between CIs and p values?

A

It is important to note the link between CIs and p-values. In general, we say that CIs and p-values are consistent: id the 95% CI for a difference excludes zero then the p value will be less than 0.05 (statistically significant)< if the 95% CI contains zero then the p-value will be greater than 0.05 (not statistically significant).

44
Q

When do you use Pearson vs Spearman correlation? [2]

A

Pearson correlation evaluates the linear relationship between two continuous variables.

Spearman correlation: Spearman correlation evaluates the monotonic relationship.

HSPH (9 decks)

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