Descriptive + inferential stats

Question 1

cumulative frequency

Answer 1

scores at or below each raw score

should be total eg 200 students in test

Question 2

percentile

Answer 2

cumulative/total number of scores x 100
displays relative standing

should be 100

Question 3

central tendency

outliers

Answer 3

what scores are most frequent
- mean
- mode
- median

outliers make mean unrepresentative of data set

Question 4

variability

Answer 4

how different scores are from each other
- range, IQR
- standard deviation

Question 5

Z-score standardised score

Answer 5

scores relative standing by how much it deviates from the mean of its distribution
- score less than mean = negative z-score
- score above mean = positive z-score

Question 6

normal distribution

Answer 6

• symmetrical about the mean
• 50% of scores above and below
• tails approach x-axis asymtotically

Question 7

z-score probability

think - normal distribution

Answer 7

normal distribution low freq scores less probable, high freq more probable
- z-score of 0 most frequent
- higher z-score = lower probability

Question 8

probability is

Answer 8

the relative frequency of an event compared to all possible events
- proportion of 0-1

Question 9

z-score normal distribution

TABLE….

Answer 9

mean = 0
SD = 1
frequency gets smaller away from the mean

CHECK IF ITS POSITIVE OR NEGATIVE SCORE WHEN USING TABLE

Question 10

z-score intervals

Answer 10

intervals –> area of scores
-1to1 = 68%
-2to2 = 95%
-3to3= 99%

Question 10

normal distribution types

Answer 10

leptokurtic = skinny up high like leaping
platykurtic = wide like playtpus
all z=0 to z=1 are 34.13% of raw scores

Question 11

How to find exact probability of particular score in distribution?

Answer 11

• need mean + SD
• convert raw to z-score
• probability in z-table

Question 12

STEPS

IQ mean 100, SD 15, what is probability of having IQ of 116 or lower?

Answer 12

1. find area of curve thats at or below 116
2. calculate z score 116-100/15 = 1.07
3. find probability on POSITIVE z-table = .85769
4. this means probability is .85769
5. percentile = 85.769%

Question 13

if m 100, SD 15, what is IQ score above which 5% of popn fall?

Answer 13

1. what score –> its at or below 95%
2. find in z-table
3. get the z-score numbers (1.64)
4. what IQ corresponds to this (Rearrange formula)
   –> 100 + 1.64x15 =124.6 IQ

Question 14

standard deviation of a distribution of sample means =

Answer 14

standard error of the mean
population SD = sigma ó, M = u(mew)
sample means SD = sigma xbar, M = u(mew)xbar

Question 15

z-tests

central limit theorem

Answer 15

using z-scores to tell aabout standing of a sample within a group
- increasing samples gives normal distribution (sample means)

theorem = samples always norm dist as long as sample is large enough

Question 16

Is a sample representative of the popn?

Answer 16

if probability is high (p>.05) sample is representative
- if probability is low (p<.05) sample is NOT representative (likelihood getting it by change is low)

Question 17

z= 2.5
z= 1.07

Answer 17

CHECK POSITIVE OR NEGATIVE
- use left side of table
- across top row then column (meet to find value)