Flashcards in L1 Craig: INTRODUCTION TO THE STATISTICAL ANALYSIS OF EXPERIMENTAL DATA Deck (25):

1

## what should uncertainty be estimated and quoted as?

### error bar

2

## what does uncertainty determine?

### precision of the measured result

3

## If you now the true value what can you do ?

### measure ether accuracy

4

## what is absolute uncertainty?

### actual magnitude of the uncertainty

5

## what is relative uncertainty ?

###
expressed as a fraction or percentage of the measured value e.g. Dx/x or 100 x Dx/x %

6

## should the uncertainty be quoted to the same level of precision as the measurement itself ?

### yes

7

## what does it mean if no uncertainty is quoted?

###
last figure in the measurement is the best that can be determined

so uncertainty is half of this

8

## what are the 2 categories of uncertainties ?

### random and systematic

9

## what's random uncertainty?

### produces a scatter of values due to random effects such as poor resolution, electrical noise, human failings; for single measurement it must be estimated; for repeat measurements it may be calculated.

10

## what is systematic uncertainty ?

### arises through incorrect calibration or mistake in experimental design often resulting in an off-set value (bias); once identified it is often possible to correct for such an error.

11

## why do we repeat measurements?

###
• Identify possible outliers–

• Calculate a mean

• Estimate the uncertainty

12

## what are outliers?

### values that appear way out of line and may be due to some one-off, gross error.

13

## When only random errors are present the best-value is.....

### average or mean

14

## In practice often only a few (n < 12) repeat measurements are available. In this case the______ is a better estimate?

### range method

15

## what is standard error?

### property of a set of measurements

16

## what is standard deviation?

### a population of numerical data through a statistical distribution

17

## what des standard error depend on?

### number of repeat measurements

18

## what's median?

### rank and its the middle value

19

## what's mode?

### most common value

20

## why is standard deviation better than mean ?

### enerally more useful as it is calculated with reference to the spread around the Mean value

21

## what's the SD formula?

### say it

22

## whats the variance of data?

### give by s^2

23

## How to calculate relative standard deviation?

### 100 x S/mean %

24

## what is RSD used to measure?

### relative precision of different sets of measurements

25