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Statistics PMR > questions and answers > Flashcards

questions and answers Flashcards

1
Q

what type of variable is a) Marital status (single, married/cohabiting, divorced, widowed)

A

nominal

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2
Q

What types of variable are the following: body temp

A

quantitative

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3
Q

What types of variable are the following : age in 10 year intervals

A

ordinal

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4
Q

What types of variable are the following : hypertension status

A

Nominal or binary

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5
Q

median definition

A

Median : the value below which 50% of obs lie. It quantifies average in the data.
-If all the values were ordered numerically, the median would be the value found in the middle

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6
Q

interquartile range

A
  • spans the values between the lower quartile (25th percentile) and the upper quartile (75th), that is the middle 50% of obs. Used to quantify variation or the amount of spread of the scores
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7
Q

when are median and interquartile ranges best used

A

when distribution is assymetrical
- We can tell this before for both groups the median is much closer to the lower quartile than the upper quartile. Median is not sensitive to extreme values and is preferred over the mean as a measure of centrality for such skewed data. IR is not sensitive to extreme values and for the same reason is proffered here over SD, as a measure of spread.

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8
Q

how can you tell if data is positively skewed

A

the median is loser tot he lower wartime suggesting the observations are concentrated on the lower (left) end of distribution

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9
Q

what is mean and how is it calculated

A
  • Quantifies the average for the quantitative variables

- Calculated by adding all values and dividing by the number of values

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10
Q

what does standard deviation mean

A
  • Variation in scores for the quantitative variables
  • The spread of data around the mean
  • ‘average difference between the scores and the mean’
  • on average how far away are the scores from the mean
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11
Q

when is SD and mean appropriate for describing data

A

when the data is symmetrical

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12
Q

weight and height

A

are well known to approximate normality- so mean and SD good stats to use

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13
Q

to be certain of which statistics to use

A

always examine variables using histograms or box and whisker plots

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14
Q

when reporting gender %

A

often papers just report the percentage of participants in one of the categories (%male)

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15
Q

The percentage change in bone mineral content and bone mineral density in two years was calculated for each individual. The authors reported that for the ultradistal forearm the change in bone mineral content was 1.14 (95% confidence interval (CI): -0.8 to 3.1) in the calcium group taking exercise and -2.6 (95% CI: -4.6 to -0.6) in the calcium only group (McMurdo et al. 1997).

What do the confidence intervals for the change in bone mineral content mean?

A

The CI is the range of values within which we can be 95% certain the true value of the parameter of interest, mean change in bone mineral content, lies in the population.

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16
Q

definition of 95% CI

A

the range of values within which we can be 95% certain the true value of the parameter of interest lies in THE POPULATION

17
Q

The authors reported that for the ultradistal forearm the change in bone mineral content was 1.14 (95% confidence interval (CI): -0.8 to 3.1) in the calcium group taking exercise and -2.6 (95% CI: -4.6 to -0.6) in the calcium only group (McMurdo et al. 1997).

Interpret the CI’s

A

So we can be 95% certain that in the calcium plus exercise group at one extreme in the truth there could be a drop of 0.8 units in bone mineral content, but at the other extreme there could be an increase in 3.1 units.
We can be 95% certain that for the calcium only group there could be a drop in bone mineral content as large as 4.6 units or as little as 0.6 units.

18
Q

The average time spent by medical students studying for an exam was estimated as 7.3 hours per day (during the week prior to the exam) with a 95% confidence interval of 6.5 to 8.1 hours. Which of the following statements are plausible? (Possible responses: Yes, No, Don’t know).
a) The 90% confidence interval was 6.4 to 8.2 hours

A
  • No, the 90% CI should be narrower than the 95% CI
19
Q

The average time spent by medical students studying for an exam was estimated as 7.3 hours per day (during the week prior to the exam) with a 95% confidence interval of 6.5 to 8.1 hours. Which of the following statements are plausible? (Possible responses: Yes, No, Don’t know).

b) The 90% confidence interval was 6.6 to 8.0 hours

A
  • Yes, the 90% CI is narrower
20
Q

The average time spent by medical students studying for an exam was estimated as 7.3 hours per day (during the week prior to the exam) with a 95% confidence interval of 6.5 to 8.1 hours. Which of the following statements are plausible? (Possible responses: Yes, No, Don’t know).
c) The 99% confidence interval was 6.5 to 8.3 hours

A
  • No- the 99% CI should be wider than the 95% CI and extend the 95% CI at both extremes- the lower bound for 99% should be lower than that for the 95% CI,not the same
21
Q

The average time spent by medical students studying for an exam was estimated as 7.3 hours per day (during the week prior to the exam) with a 95% confidence interval of 6.5 to 8.1 hours. Which of the following statements are plausible? (Possible responses: Yes, No, Don’t know).
d) The true average time spent by students could plausibly be 6.5 hours at the 95% level of confidence and the 99% level

A

Yes- if the 95% CI includes 6.5 hours then the 99% CI must also include 6.5 hours, so the value is plausible under both

22
Q

The average time spent by medical students studying for an exam was estimated as 7.3 hours per day (during the week prior to the exam) with a 95% confidence interval of 6.5 to 8.1 hours. Which of the following statements are plausible? (Possible responses: Yes, No, Don’t know).
e) All students study for at least 6.5 hours per day

A
  • No- we cannot tell the min or max value in the sample from CI.
  • The 95% CI quantifies the precision in the estimated mean
  • It does not directly tell us what the variability is across students in the same with respect to the time spent studying
  • If we wanted to summarise variability we could report 95% range
23
Q

will the CI’s be wider for 95% CIs or 99%

A

99%
- the 99% CI should be wider than the 95% CI and extend the 95% CI at both extremes- the lower bound for 99% should be lower than that for the 95% CI,not the same

24
Q

CI’s tell us noting about

A

means

Statistics PMR (7 decks)

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