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Research And Statistics > Basic Statistics > Flashcards

Basic Statistics Flashcards

1
Q

What is an observation ?

A

The units on which we measure data, such as persons, cars, animals… are called observations.

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2
Q

What is a population ?

A

A collection of all units

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3
Q

What is a sample ?

A

A selection of n observations. A sample is always a subset of the population

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4
Q

What is a qualitative variable ?

A

Variables which take value that cannot be ordered in a logical or natural way.

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5
Q

What is a quantitative variable ?

A

Variables that represent measurable quantities. The values which these variables can take can be ordered in a logical and natural way.

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6
Q

What is a graphic ?

A

It represents the relationship between two or more variables
It is an alternative way to summarize a variable’s information
It provides clues that words and equations do not
It is great tool to form hypotheses and draw conclusions

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7
Q

What is a disadvantage of graphs

A

They can be inaccurately interpreted, resulting in incorrect answers or conclusions

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8
Q

What is the pie chart used for ?

A

Used to visualize the absolute and relative fréquences of nominal (categorical) and ordinal variables

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9
Q

What is the bar chart used for ?

A

Used to visualize the absolute and relative frequencies of observed values of a variable. Can be used for nominal and ordinal variables.

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10
Q

What is the histogram used for ?

A

Used to visualize the distribution of values of continuous variables.

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11
Q

What are the differences between bar charts and histograms ?

A

Histograms shows the distribution of variables whereas bar charts compare variables
Histograms show quantitative data whereas bar charts show categorical data
The bars in an histogram cannot be reordered

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12
Q

What is line graph used for ?

A

Used to visualize quantitative data collected over a specific topic and a pecific time interval.
Data points are connected by a line, and they represent the observation.

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13
Q

What are box plots used for ?

A

Used to visualize the distribution of data based on a five number summary : minimum, first quartile, median, third quartile, maximum.

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14
Q

What is Q2 ?

A

The middle value of the data = the median

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15
Q

What is Q1 ?

A

The lower quartile, the middle number between the smallest and the median

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16
Q

What is Q3 ?

A

The upper quartile, the middle value between the median and the highest value

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17
Q

What is the interquartile range ?

A

From Q1 to Q3

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18
Q

How to determine the lower extreme in a blox plot graph ?

A

Lower extreme = Q1-1,5*IQR
Where IQR = Q3-Q1

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19
Q

How to determine the upper extreme in a box plot chart ?

A

Upper extreme = Q3+1,5*IQR
Where IQR=Q3-Q1

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20
Q

What are scatter plots used for ?

A

Used to visualize the relationship between two quantitative variables measured on the same individuals.
It is useful to visually detect outliers
It shows the type of relationship between two variables

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21
Q

What are tables useful for ?

A

Used to present results from research, e.g., within or between-group comparisons.

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22
Q

What is an outlier ?

A

An outlier represents a value distant from the rest, due to variability or error.
Outliers are value more than 1,5 time the IQR

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23
Q

How to detect an outlier ?

A
  • visually inspect data using a scatter plot or box plot
  • use Tukey rule to detect outliers :

Q1-1,5IQR
Q3+1,5IQR

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24
Q

What is a correlation ? What is it useful for ?

A

Correlation is used to test the relationship between variables (quantitative or categorical)
It is a measure of how things are related.
Some correlations are high
Some correlations are low

It is useful to make predications about future events

25
Q

Which graph is the most appropriate to read a correlation ?

A

The scatter plots graph
Adding a trend line will help to show the tendency behavior between variables

26
Q

How to read a correlation between interval or ratio variables ?

A

Using the correlation coefficient or Pearson coefficient «r»
«r» describes the strength and direction of the linear association between two continuous (interval or ratio) variables.
«r» varies from -1 (negative strong correlation ) to 1 (positive strong correlation)
0=no correlation

27
Q

How to read a correlation between qualitative ordinal scale variable ?

A

Using the Spearman correlation coefficient

28
Q

In the context of correlation of ratio/interval variables, what is «r square» ?

A

The coefficient of determination : the ratio of the amount of variance explained by the regression model to the total variation in the data

29
Q

What is reliability ?

A

It is the overall consistency of a measure.
There is high reliability if a measure produces similar result under consistent conditions

30
Q

What is the reliability test for categorical variables ?

A

Percent agreement or k-statistics - Cohen’s K

31
Q

What does the k-statistic determines ?

A

It determines how well an observation produces the same value for the same patient on repeated measurements (ideally two examiners)
It determines:
- intra and inter examiner reliability
- intra and inter session reliability

32
Q

How to calculate the % of raw agreement ?

A

((Sum of normal observations)+(sum of abnormal observations))/total observations

We do the sum of agreed observations and divide them by that total number of observations

33
Q

What is the purpose of crosstabulation ?

A

The purpose of crosstabulation is to show in tabular format the relationship between tow or more categorical variables.

34
Q

How to interpret K-statistics

A

0-.59 : weak
0.60-0.79 : moderate
0.80-0.90 : strong
Above 0.90 : almost perfect

35
Q

What means k=0

A

Represents the amount of agreement that can be expected from random chance

36
Q

What means k=1

A

Represents the perfect agreement between the raters

37
Q

What means k=-1 ?

A

Represents great disagreement among raters (or no agreement)

38
Q

For what is k-statistic used for ?

A

It is used as a measure for quantifying agreement beyond chance for categorical variables

39
Q

How to determine K in Kappa statistics ?

A

K=((Po-Pe)/(1-Pe)
Where :
Po is the percent agreement observed = raw % agreement
Pe is the percent agreement expected

40
Q

What is the coefficient of variation ?

A

For continuous variables, the coefficient of variation (CV) provides a very simple way to determine the relationship between the standard deviation and the mean of two sets of observations
Values close to zero show minimal variation

41
Q

How to determine the CV ?

A

CV=(standard deviation/mean)*100

42
Q

What is the interclass correlation coefficient ?

A

Is another reliability measure to use in continuous variables
Ranges between 0 and 1, ans is always associated to a 95% confidence interval

43
Q

What is the standard error measurement ?

A

A test of reliability
An estimation of the expected random variation in scores when no real change has taken place

44
Q

What is detectable difference (or change)

A

A test of reliability
The minimum amount of change that needs to be observed at either the group or individual level for it to be considered a real change

45
Q

What is inferential statistics ?

A

It refers to the generalization of results from a sample of participants to the whole population.

46
Q

Why is it helpful to use inferential statistics ?

A

-making inferences about the population from the sample
- concluding whether a sample is significantly different from the population
- if one model is significantly better than the other
- hypothesis testing in general

47
Q

What is the most used method of inferential testing ?

A

Hypothesis testing

48
Q

What is hypothesis testing ?

A

It determines the probability (p-value) of difference, or non-difference between groups

49
Q

In hypothesis testing, what is p-value ?

A

The p-value provides evidence against the null hypothesis H0
The smaller p-value is, the stronger the evidence against H0 and in favor of the alternative hypothesis Ha
If p-value is equal or inferior to 0,05, then H0 is rejected in favor of Ha

50
Q

What is the null hypothesis ?

A

The one we want to disprove

51
Q

What is the Chi-square test used for ?

A

Is used to determine if there is a significant association between two categorical variables
The test compares the observed values with the expected.

52
Q

What determines the T-test ?

A

The t test tells us how significant the difference between group means are

53
Q

What are the requirements for the T-test?

A

-continuous variables
-normal distribution
-equal variance in the samples

54
Q

What are the three types of T-tests ?

A

Paired sample T-test
Independent sample T-test
One-sample T-test

55
Q

What is the paired samples T-test ?

A

Used to compare the means between two sample from the same group/individual
Comparing the means of two conditions. Where the same people are in both groups

56
Q

What is the indépendant samples T-test used for ?

A

Used to compare means between two samples from different groups/individuals
Comparing the means of two different groups

57
Q

What is the one-sample T-test used for ?

A

Comparing the mean of a sample with a pre-specified mean

58
Q

What are the 3 questions answered to by each type of T-test ?

A
  • can I be certain that the difference between groups is not due to random chance ?
  • how big is the difference ?
  • is this difference important ?
59
Q

In T-student test, what is t-value ?

A

The degree to which the difference can be explained by the group
It is compare to a threshold value
t>0,05 : assumes Ha, and the difference is significant
t<0,05 : assumes H0 the difference is NOT significant

Research And Statistics (4 decks)

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