Chapter 2 - Distributions of Scores Flashcards

Question

what is the difference between subjective and objective probability?

Answer 1

* Subjective Probability expresses individual’s subjective judgement about the likelihood of something occurring: “I’ll probably do well on the exam!” * Objective Probability expresses the numerical likelihood of some event occurring (say flipping a coin: 50/50 chance)

Answer 2

qualitative variable: heads or tails

Answer 3

every time you flip the coin

Answer 4

Nsucesses/Nse (sampling experiments)

Answer 5

p = 6/60 = 0.1

Answer 6

by proportion (number between 0 and 1) A die has 6 sides * If we want to count the number of time I roll a one ( 1 ) out of sixty ( 60 ) trials, how would I do this? * If I roll a one six times

Answer 7

* An Event is one or more of the possible outcomes of a sampling experiment * If we said the success in the last example was rolling a 3 or a 6, then the event is a 3 or a 6 * We can compute the proportion of times an event occurs in the same way we computed the proportion of time an outcome occurs, e.g.: * 75 rolls, fourteen 3s and sixteen 6s * p = (14 +16) / 75 = 0.4

Answer 8

the proportion of time the event would occur if the same sampling experiment were repeated infinitely many times

Answer 9

* Probability intimately related to our use of distributions in statistics * Given any distribution of scores, we can define a number of events * “Score is greater than x” * “Score is less than x” * “Score is between x and y” * “Score is outside the interval x to y”

Answer 10

1. the event MUST occur 2. the event will NEVER occur 3. not possible 4. 1.00

Answer 11

If you are asked the probability of x OR y occurring, you add the probability together

Answer 12

if you are asked the probability of x AND y occurring, you multiply the probabilities

Answer 13

cannot co-occur: a coin can come up heads or tails, but NOT both

Answer 14

occurrence of one event does not affect the probability of the other * If two coins are flipped and one comes up heads it has no affect on the results of the other coin

Answer 15

occurrence of one event does affect the probability of the other - drawing from a deck of cards without replacement (/52, /52, etc.)

Answer 16

OR RULE Three heart cards also have faces, these events are not mutually exclusive, so we need to remove the cards we counted twice pHeart = ( 13/52 ) pFace = ( 12/52 ) pHeart&Face = ( 3/52 ) 22 / 52 = .42

Answer 17

AND RULE pBaby1 = ( 1/2 ) pBaby2 = ( 1/2 ) ( 1 / 2 ) * ( 1 / 2 ) = ( 1 / 4 ) = .25 .5 * .5 = .25

Answer 18

If the queen is put back into the deck, then on 2nd draw there will still be 52 cards in the deck pQueen = ( 4/52 ) pKing = ( 4/52 ) ( 4/52 ) * ( 4/52 ) = .005917

Answer 19

If the queen is not put back into the deck, then on 2nd draw there will now only be 51 cards in the deck pQueen = ( 4/52 ) pKing = ( 4/51 ) ( 4/52 ) * ( 4/51 ) = .006033

Answer 20

conveys the probability that a randomly selected score will have a given value or fall in a given interval

Answer 21

* Probability intimately related to our use of distributions in statistics * Given any distribution of scores, we can define a number of events * “Score is greater than x” * “Score is less than x” * “Score is between x and y” * “Score is outside the interval x to y”

Answer 22

* Probability Density Functions: plots the density of scores at each value of a continuous variable * This shows a hypothetical distribution of heights measured in inches. * There are more scores around the centre of the distribution * The number of scores decreases as we move away from the center.

Answer 23

* Density is the proportion of scores in an interval divided by the interval width * d = p / w * p is the proportion of scores * w is the width * For each value of x, there is a single density * The area under the curve is equal to 1