HS312: Epidemiology and Biostatistics II - 1505A

Print by: Erittnee Robertc tls312: Epidemiology and Biostatistlcs II - 15O5A / HS312 Unit 1O Assignment

Unit 6, Topic 24, Exercise 24-25 Suicides

Many songs associate Mondays with having the-b_lues, but are people really more.likely to commit suicide

on MondaysZ e recent study iXposowa et 5t., ZOOST analyzed.data on suicides in the United States

between the years 2000 an'd zcio+. rnev cr#sineo Lach juicide according to the day of the week on which

it occurred. Their data produced the following sample percentages:

A news article that described this study did not report the sample size' Suppose for now that the sample

size was 252 . ftg computer output below presents results of a chi-square goodness-of-fit test of equal

proportions:

L 41- =L.l'-r.l- ir

i_

t

tr

6

Dbserve-i 3CI

l6 i3 6?.

2B ?s i6

1L i-c.-LI-r -'r4 '-l -' ??'ic5-).4 | lV

Test F'r,:port i'::n

^. . ,{.-}eqf h, 'r'icr-? u . -=4Qi

;

^ ;rt?CtrTu r -ts44i ir, i/n;<J

3. -42851 0.:l-4:857 i. i-4:85?

L'-r.ra IL:e 0.i0i

Expectecl l6 3E 36 Jb 3b 36 Jll

l]nntrihut ir,n t'r ihi-Sq

' . i'000 0 . nCItl0 0.4,{4,1

i8.77?B l-.???8 1-.7?T8 0.i0CI0

a:

152 DF

6

a. Explain how the expected counts were calculated'

f The percentage of suicides for each day is multiplied by the sample size'

r The percentage of suicides for each day is divided by the sample size.

r The sample size is divided by percentage of suicides for each day.

6* Seven is divided by the sample size.

f The sample size is divided by seven. b, Choose how the chi-square contribution for Monday was calculated.

(30 - 36)2

36*30 36

{30 - 361?

r 36

r 3q-30 6

r

r wz -- lfz 36

c. Interpret what the P -value means in this context-

{* The P -value is the probability of obtaining sample counts that result in a large chi-square test statistic, assuming that the probability of a suicide on each of the seven weekdays is not the same.

f The P -value is the probability of obtaining sample counts that result in a small chi-square test statistic, assuming that the probability of a suicide on each of the seven weekdays is the same.

f The P -value is the probability of obtaining sample counts that result in a small chi-square test statistic, assuming that the probability of a suicide on each of the sven weekdays is not the same.

{- the P -value is the probability of obtaining sample counts that result in a large chi-square test statistic, assuming that the probability of a suicide on each of the seven weekdays is the same'

d. Summarize the conclusion that you would draw from this P -value.

? You have no statlstical evidence that the pmbability of a suicide occuring on any of the seven weekdays is not the same.

1- You have weak statistical evidence that the probability of a suicide occurring on any of the seven weekdays is not the same.

.* You have strong statistical evidence that the probability of a suicide occurring on any of the seven weekdays is not the sarrc.

e. Which day appears to be especially likely for sukides?

1* Monday 1^ Tuesday

3- Wednesday 1^ Thursday g. Frtday {: SaturdaY

t

f Sunday f, If the sample size were larger, and the sample percentages stayed the same, how would tfre P -value change?

{^ The P -value would increase.

r The P -value woutd decrease.

f Tlre P -value would stay the same.

Qucsfion Attenp&: O of 5 uced

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