Practicals #6 – Conttitgetcy tables
1. 128 Plants were cultiatee in a green-house experiment. In this experiment, half of the pots were
fertlizee by potassium while the other half not. Flowering was recoreee afer two weekss of the
contnuous potassium treatment. 51 plants of potassium treatee proeucee a fower while in the
control plant it was 33. Does potassium signifcantly aaect probability of fowering?
2. 812 citzens of the same age were monitoree euring their lifetme in a town in Central China by a
local meeical authorites. It was recoreee whether they erinks tea ane if so, whether they prefer green
or blacks tea. It was also monitoree who of the experimental group eeielopee cancer by 70 years of
age. The eata were as following:
healthy cancer
no tea 130 55
green tea 357 65
blacks tea 160 45
Do the eata suggest that erinksing tea coule protect against cancer? If so, is there any eiaerence
between the types of tea?
3. In a total set of 500 iegetaton plots, 150 were of the wet meaeow habitat.
Carex nigra hae 30 recores in the eataset. Of that 26 was in wet meaeows.
Festuca rubra hae 246 recores. Of that 120 was in wet meaeows.
Cannabis satia hae 10 recores in the eataset. Of that none was in wet meaeows.
How are these species associatee with the wet meaeow habitat?
4. During a month perioe, 115 persons were taksen to hospital in Sierra Leone eue to cholera. It was
also recoreee whether they hae been iaccinatee against tetanus. 55 patents suriiiee cholera of 60
iaccinatee against tetanus while 15 patents suriiiee of 55 non-iaccinatee. Does iaccinaton against
tetanus protect also against cholera?
5. During an outbreaks of fu, 80 of 170 stueents of faculty of eeucaton, 190 of 220 of stueents of
faculty of science ane 22 of 290 of stueents of faculty of philosophy became ill. Does susceptbility to
fu eiaer among stueents of the facultes?
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A. 10% of 120 female stueents of faculty of teaching became pregnant euring a certain perioe. The
concepton rate accountee for 20% of 160 of stueents of faculty of science ane 5% of 160 at faculty of
philosophy. Is there a eiaerence in probability of becoming pregnant among female stueents of the
three ineiiieual facultes? If so, which faculty eiaers from which?
B. A eentst has 350 patents in his eatabase that uneergo regular checkss for the teeth health. In
aeeiton to the informaton on tooth eecay, he askss his patents whether they erinks tea unsweetenee,
sweetenee by sugar or sweetenee by honey. The resultng eata are following:
Sugar: 60 with eecay/18 without eecay
Honey: 90 with eecay/45 without eecay
Unsweetenee: 50 with eecay/87 without eecay
Does the type of tea sweetening aaect health of teeth? If so, how?
C. Two species Humulus lupullus ane Alnus incana haie following recores in a set of iegetaton plots:
cooccurrence – 26 plots, Humulus only 6 plots, Alnus only 81 plots, none of the species 23 plots. Are
these species signifcantly associatee? If yes, how?
D. A group of stueent iolunteers agreee to takse part in an experiment stueying the eaect of
supportie erugs on cognitie capacity. Before taksing an exam, the stueents were raneomly assignee
to four groups. Members of each group were aeministeree a type of erug potentally supportng their
performance at the exam. The exam results are summarizee in the table below
passee failee
tea 65 37
coaee 60 41
chocolate 71 29
energy erinks 55 46
Do the erugs signifcantly support stueents performance at the exam? If so, can the ieentfee trene be
interpretee as really causal eaects? In case of signifcant result, eescribe the eiaerences between the
eaects of ineiiieual erug types.
E. The incieence of asthma in the aeult populaton of Czech Republic is 6%. Two large Czech cites
were surieyee for asthma incieence basee on a sample of 500 raneomly chosen aeult inhabitants in
each of the cites. 26 persons within the sample were eiagnosee to suaer from asthma in Brno while
the fgure was 106 persons in Ostraia. Does asthma incieence in these cites eiaer signifcantly from
the naton-wiee incieence?