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BMS1042 > BIOSTATS > Flashcards

BIOSTATS Flashcards

1
Q

What is ordinal data?

A

Observations that can be ordered/ranked according to some criteria. e.g. on a scale such as 1-10 or asking someone if there pain is high,medium or low.

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2
Q

What is nominal data?

A

When observations are classified into separate categories that have no logical ranking e.g blood types AB, O .

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3
Q

Is the data nominal or ordinal if there are only two categories? (binary data)

A

Always nominal

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4
Q

Smoking status of visitors of trauma patients at The Alfred (strict no-smoking policy) in 2010. (NOMINAL, ORDINAL, CONTINUOUS OR DISCRETE??)

A

Categorical, nominal

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5
Q

The standard categories of Body Mass Index: < 18.5 (underweight), 18.5 – 25 (normal), 25 – 30 (overweight) and ≥ 30 (obese). (NOMINAL ORDINAL CONTINUOUS OR DISCRETE???)

A

Categorical, ordinal

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6
Q

ody Mass Index, calculated using patient weights and heights. (NUMERICAL, ORDINAL NOMINAL OR DISCRETE??)

A

Numerical, continuous

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7
Q

Can the sample size be bigger than the population size?

A

YES. it can bigger than the population size if redundant samples are taken

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8
Q

When is SRS (Simple Random Sampling) used?

A

Simple experiments tat require a single sample to be taken from a population , target group is large,

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9
Q

When is stratified sampling used?

A

Used it when there are smaller sub-groups that are to be investigated, you want to achieve greater statistical significance in a smaller sample and use it to reduce standard error.

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10
Q

Proportionate stratified sampling

A

takes the same proportion (sample fraction) from each stratum

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11
Q

Disproportionate stratified sampling

A

takes a different proportion from different strata. This may be done to ensure minorities are adequately covered.

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12
Q

When is cluster sampling used?

A

Used when the studied population is spread across a wide area such that simple random sampling would be difficult to implement in accessing the selected sample

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13
Q

When is Snowball sampling used?

A

When you do not have access to sufficient people with the characteristics you are seeking

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14
Q

What is the parameter?

A

Characteristic of interest in the entire population, it is fixed value, e.g. Mean cholesterol level of all Asian males in Melbourne

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15
Q

What is the bernoulli distribution used for?

A

Only sample sizes of 1 so rarely used.

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16
Q

What is a binomial distribution?

A

Two mutually exclusive events. Probability of interest unknown (pi). The number of times an outcome repeats itself in data set.e.g. how many times did you role a 6 on a dice?

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17
Q

What is another name for the ‘normal distibution’?

A

Gaussian distribution

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18
Q

What type of distribution occurs when the mean < median

A

Negatively skewed

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19
Q

What type of distribution occurs when the mean>median>mode?

A

Positively skewed

20
Q

What type of summary statistics do you use for normal distribution?

A

Mean and SD

21
Q

What type of summary statistics do you use for asymmetric (left or right skewed) data?

A

Median and IQR

22
Q

In the normal distribution where do 68% of values lie?

A

Within +- 1 SD (mean + or - 1SD)

23
Q

In the normal distribution where do 95% of values lie?

A

+- 2SD

24
Q

In the normal distribution, where do 99.7 % of values lie?

A

+- 3SDs

25
Q

What is the z score formula?

A

Zscore= Observed value- True mean/True SD

26
Q

What is the T distribution?

A

Very similar to normal distribution (symmetric and bell shaped) BUT bell peak of curve is FLATTER than normal distribution and tails are LONGER.
- Has df which are degrees of freedom

27
Q

What is standard error?

A

The dispersion (spread) of the sampling distribution
- Measures how precise the population mean is estimated by the sample mean
(technically is the standard deviation of the sample mean)

28
Q

When do we use the z score?

A

When the population (true) standard deviation is KNOWN

29
Q

When do we use the T score?

A

When the Population (true) standard deviation is UNKNOWN and we only have the SAMPLE ST DEV

30
Q

When would we use the standard deviation?

A

If we are describing the spread of observations in a study

31
Q

When do we use standard error (SE)?

A

If using a sample to infer population results

e.g. Mean testosterone levels in elderly women in the population

32
Q

As the sample size increases, what decreses?

A

Standard Error (SE)

33
Q

If the SD is large then ____ is also large

A

If the SD is large, then SE is also large

34
Q

What is the 68, 95, 99.7 rule?

A
  • 68% of sample means expected to lie between 1SE of mean
  • 95% of sample means are expected to lie between 2SE of mean
  • 99.7 “”
35
Q

What are the break downs for the distribution percentages (to add up to 99.7)?

A
  • 34, 34, 13.5, 13.5, 2.35, 2.35 =99.7 (reference ranges)
36
Q

What do we use if reference ranges (34,34 etc.) don’t apply?

A
  • The Z or T score
37
Q

What is a type I error?

A

When we reject the null hypothesis when it is true (false positive) e.g. telling man he is pregnant
Reject the null hypothesis when in reality the null is true – Type I error

38
Q

What is a type II error?

A

When we retain the null when it is false (false negative) e.g. telling pregnant women she is not pregnant

39
Q

What is the null hypothesis?

A
  • Population mean 1- Population mean 2=0
40
Q

What does variance equal?

A
  • SD^2
41
Q

What are the 3 assumptions for an independent T test?

A
  1. Two groups are independent
  2. People within each group are independent
  3. Birth weight in each group follows a normal distribution
42
Q

What can the P value 0.05 help with in terms of type I and II errors?

A
  • Fixing the type I error and minimising type II error or maximising power
43
Q

What does a P value of 0.001 mean?

A
  • this means that if 1000 similar studies were undertaken on the same population, only 1 out of 1000 studies would result in a sample result as extreme as the one obtained in this study due to sampling variability or by chance
  • The study result is so rare that a chance factor can be ignored for the difference from the hypothesised value
44
Q

In practice, we prefer higher confidence levels and narrower widths. A narrower width indicates smaller sampling variability and high precision. T/F

A

T

45
Q

The width of a confidence interval can be reduced without reduction of confidence level by decreasing the sample size. (T/F)?

A

F

If the sample size increases, the standard error decreases which results in a narrower confidence interval.

BMS1042 (7 decks)

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