Statistik

Question 1

Vad innebär negative growth rate?

Answer 1

Exempelvis att Working age people decreases because less childen are born, and non working people (60–>) increases because people live longer.

Question 2

Vilka är the four basic steps in statistics?

Answer 2

1. Gathering data
2. Understanding data
3. Modeling of data
4. Conclusions from data

Question 3

What does population means?

Answer 3

A gathering of all elements with something in common.

Ex: The total number of students in a city

Question 4

What is sample?

Answer 4

A collection of elements drawn from the population.

A sample is a smaller, manageable version of a larger group

Question 5

What is sampling frame?

Answer 5

A list of all the elements of population or the source material or device from which the sample is drawn.
It is a list of all those within a population who can be sampled, and may include individuals, households or institutions.

It’s a complete list of everyone or everything you want to study

Question 6

What is the different between a population and a sample frame?

Answer 6

The population is general and the frame is specific.
For example, the POPULATION could be “People who live in Jacksonville, Florida.”
The SAMPLE FRAME would name ALL of those people, from Adrian Abba to Felicity Zappa.

Question 7

What does it means that the sample frame is Over coverage?

Answer 7

That the sampling frame contains elements that are not a part of the population

Question 8

What does it means that the sampling frame is under coverage?

Answer 8

That there are elements in the population that are not included in the sampling frame.

Ex. 100 homeless people, but only 90 registered.

Question 9

What are the 4 levels of data?

Answer 9

1. Nominal data
2. Ordinal data
3. Interval data
4. Ratio data

Question 10

What defines Nominal data?

Answer 10

Nominal data is the lowest level of data.

It can be classified into categories and they have no natural order.

Ex: gender (male/female), eye color etc.

MODE!

Question 11

What defines ordinal data?

Answer 11

The second lowest level of data.

It can be classified into categories with natural order and the order is significant.

Measured of non-numeric concepts lie satisfaction, level of happiness etc.

Ex: order from Very satisfied to not at all satisfied.

MODE & MEDIAN!

Question 12

What defines interval data?

Answer 12

The second highest level of data

The data is numerical but lacks an absolute zero, meaning that when the measure is zero, there is nothing at all.

Interval scale tells us about the order and also about the value between each item.

Ex: Temperature, time. (Kan inte va = 0)

MODE, MEAN & MEDIAN!

Question 13

What defines ratio data?

Answer 13

The highest level of data.

Has an absolute zero.

Ex: Lenght, weight, temperature in Kelvin scale.

MODE, MEAN & MEDIAN!

Question 14

Which measurement is best to use when the data has outliers or extreme values?

Answer 14

Median.

Question 15

Mean kan be effected by outliers/extreme valuer, true or false?

Answer 15

True. And therefore mean is not a good option to use when we have outliers or extreme values.

Question 16

What does it mean if the modal percentage is close to 100?

Answer 16

That the spread is small.

Question 17

What defines the upper quartile (Q3) ?

Answer 17

That it has 25% of the observations above it and 75% below.

Question 18

What is the IQR, Inter quarter range?

Answer 18

The difference between Q3-Q1.

Question 19

What is an outlier?

Answer 19

An observation that is distance from the other observations.
Outliers can upcome because of variability in the measurement or because of a experimental error (datafel).
They are sometimes excluded from the data set.

If a datapoint is below: Q1 -(1.5xIQR)
OR above: Q3+(1.5xIQR)

Question 20

What is an extreme value?

Answer 20

When a data point is below: Q1-(3xIQR)

OR above: Q3+(3xIQR)

Question 21

What does cause and effect mean?

Answer 21

That one variable is the cause of the other ones effect. Ex:
x –> y = outdoor temp bestämmer indoor temp
x y = de påverkar varandra, ex vid income and consumption.
x y. En variabel påverkar två andra.
x, y —> ingen relation mellan dem.

Question 22

What are the important points in correlation?

Answer 22

It is a numerical measure of relationship between two variables.

The sign of correlation relates to the slope of best fitting line through x and y.

Correlation does not imply causality (orsakssamband)

Question 23

“r” measures something, what?

What does the value lie in-between ?

Answer 23

That there is no LINEAR relationship between two variables.

-1 < r > 1

Question 24

What is interpolation?

Answer 24

Interpolation is an estimation of a value within two known values in a sequence of values.

Question 25

What is Extrapolation?

Answer 25

extrapolation is the process of estimating, beyond the original observation range,

Question 26

What is the quartile? How is it constructed in the data set?

Answer 26

The quartile is constructed as four equal sizes of quartiles , which you set up for your data to measure variation and spread. The quartiles are the three values that split a data set into four equal parts.

Question 27

How do we use the quartile to measure spread?

Answer 27

Calculate Q3-Q1 and then we can se how much spread out the middle 50% of the data is.

Question 28

What defines a negatively skewed distribution?

Answer 28

That it has a tail to the left. | Mode>Median>Mean

Question 29

What does Standard error mean?

Answer 29

It's the AVERAGE distans between an observation and the estimated regression line. Measures the average size of a residual

Question 30

Vilka är de olika "stegen" på standard deviation?

Answer 30

1 Standard deviation = 68% 2 Standard deviation= 95% 3 Standard deviation = 99%

Question 31

What does standard deviation measure?

Answer 31

Measure the amount of variation of data values. | the further away from the mean, the higher standard deviation.

Question 32

What does (R2) coefficient of correlation measure? what does r=0 indicate?

Answer 32

The strength of a linear relationship between two known variables. r=0 indicates that there is no LINEAR relationship, but there can still be a relationship.

Question 33

If a histogram is right (or positive) skewed, which is bigger, the mean or the median? Explain why!

Answer 33

The tail is drawn towards the right i.e. towards higher values which makes the mean a higher value and larger than the median because the mean is also pulled towards the right.

Question 34

Given an example of how under coverage can bias (systematically change) the result of a survey.

Answer 34

Say that you want to examine students at university west. The sample frame that you use does not include students from the engineering department. When asking questions about attitude towards technique you would get biased answers since engineering students likely to be fonder of technique than other students

Question 35

For adult Swedish males age 50 the average weight is 84 kg and the standard deviation is 12 kg. How should the standard deviation be interpreted in this setting?

Answer 35

On AVERAGE the weight of a man deviates from 84 kg with 12 kg. This means that some weigh 15 kg more some 5 kg less and so on but on AVERAGE the deviation is 12 kg.

Question 36

Explain how the coefficients a and b in simple linear regression are estimated using the method of least squares. Explain the basics of the method of least squares.

Answer 36

The least square method finds the line of the best fit for a data set, the line should be as close as possible to the data. The line will explain the potential relationship between a dependent and one independent variable.

Question 37

The correlation between “Exam score” and “hours spent revising” is 0,82, what does this mean? What would a correlation of 0 mean?

Answer 37

This means that there seems to be some linear relationship between the two variables. Since the correlation is positive it means that when one of the variables is big the other tends to be big as well. If the correlation was 0 this would mean that there is no linear relationship between the variables.

Question 38

Explain how the residuals for a regression model is calculated and give at least one possible source of variation in the residuals

Answer 38

The residuals are calculated by subtracting the estimated value of the observation from the actual observation using the linear model. Two possible sources of variation is: Random measurement errors and model error, i.e. using a linear model when for instance the true relationship is quadratic.

Question 39

Explain the mode and mode proportion

Answer 39

The mode is a measure of location for nominal or ordinal data with few categories. The mode is the most commonly occurring category, i.e. the mode is a category. The mode proportion is a measure of spread used for the same data types as the mode. It is the proportion of the answers that the mode has, i.e. the mode proportion is a number. The higher the mode proportion the less spread in the data and the lower the mode proportion the higher the spread.

Question 40

When is the variable income statistically significant?

Answer 40

When the value in the ”sig”-column is lower than 0,005 (0,5%)