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Statistics > Data and distributions > Flashcards

Data and distributions Flashcards

1
Q

Fundamental features of a dataset

A

Datapoints (n)
Measures of central tendency (mean, variance, SD)
Type of distribution

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2
Q

Key properties of the normal distribution

A

Continuous data
Bell shaped curve

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3
Q

How do we define the normal distribution?

A

By the mean and SD

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4
Q

In normally distributed data, 95% of the data lies within…

A

1.96 SDs of the mean

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5
Q

Properties of the Poisson distribution

A

Discrete data
As the mean gets bigger, the distribution becomes more like the normal distribution

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6
Q

When the mean is > ___ you can approximate the Poisson distribution with a _____ distribution

A

5
Normal

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7
Q

Poisson distributions are right-skewed for ____ means

A

Low

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8
Q

As the mean gets _____ in a Poisson distribution, it gets more like the _____ distribution

A

Bigger
Normal

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9
Q

Properties of the Binomial distribution

A

Discrete variables
Defined by the number of trials and the probability of one of two possible events happening

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10
Q

How do we define the Poisson distribution

A

By the mean
Mean = variance

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11
Q

How do we define the Binomial distribution?

A

Number of trials (n)
The probability of one of two events happening (p)

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12
Q

When p is low in the Binomial distribution, we see a _____ skewed distribution

A

Right
(Most of the time the event will not happen)

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13
Q

When p is very high in the Binomial distribution, we see a _______ skewed distribution

A

Left
(Most of the time the event will happen)

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14
Q

As p increases in the Binomial distribution, the distribution becomes more…

A

Bell shaped (like the normal distribution)

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15
Q

What sort of data is normally distributed?

A

Means of samples of random variables
Quantities that are the sum of many independent processes
Body temp
Brain size

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16
Q

What sort of data is Poisson distributed?

A

Counts of independently occurring events in homogenous units
E.g. Quadrat sampling

17
Q

What sort of data is Binomially distributed?

A

Counts (or proportions) of ‘successes’ vs ‘failures’ out of a fixed number of trials, where the probability of success is constant
Number of ‘heads’ in 10 coin flips
Proportion of a population with a particular mutation
Number of adult frogs developing from fixed initial number of tadpoles

18
Q

What is the 95% confidence interval for a mean?

A

An interval of numbers that will contain the true value of the mean 95% of the time

19
Q

How to calculate standard error of the mean

A

standard deviation / root(n)

n = sample size

20
Q

As the sample size increases, standard error gets _____

A

Smaller
As n increases, so does root n, so the standard deviation is being divided by a larger number and therefore gets smaller

21
Q

The smaller the sample size, the _____ the confidence interval needs to be to ensure an x% chance of containing the true value of the mean

A

Wider

22
Q

When we don’t know the standard deviation of the population precisely, we have to use ______ to calculate the confidence interval

A

A t-distribution

23
Q

How to calculate a confidence interval

A

CI = mean +/- tcrit x SE

24
Q

Approximate rule of thumb for 95% CI

A

mean +/- 2 x SE of the mean

25
Q

The 95% confidence interval is _____ than the 99% confidence interval

A

Narrower

26
Q

What is the null hypothesis?

A

There is no significant difference between the populations we are looking at

27
Q

What is the alternative hypothesis?

A

The hypothesis that something will happen (there will be an effect of a drug, two groups will be different etc)

28
Q

What is a two-tailed test?

A

A hypothesis test where we don’t have any reason to suppose that the effect will be in a particular direction

29
Q

What is a one-tailed test?

A

A hypothesis test where we have reason to believe that the difference will be in a specific direction

Statistics (3 decks)

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