praktikum epidemi dasar rev

TWOXTWO - calculates sensitivity, specificity, probabilities and

predictive values from 2X2 tables. Enter data in C8, C9, D8 & D9.

[Press F9 to calculate]

Actual Health Status

Test Result D+ D-

------------- ------------- ------------- ------------- ------------- -------------

T+ | 40 10 | 50

T- | 10 490 | 500

------------- ------------- ------------- ------------- ------------- -------------

50 500 | 550

Prior Prob. of dis. (True Prevalence) = p(D+) = ................... 0.091

Sensitivity (ability ot detect dis.) = p(T+/D+) = ................... 0.800

Specificity (ability to detect non-dis.) = p(T-/D-) = .......... 0.980

Post-test Prob. of dis. given T+ = p(D+/T+) = ................ 0.800

(Predictive Value of a Positive Test)

Post-test Prob. of dis. given T- = p(D+/T-) = ................. 0.020

(1 - Predictive Value of a Negative Test)

Apparent Prevalence = p(T+) = ............................ 0.091

CHISQ - Calculates rates and chisquare statistic for cross-sectional,

case-control and cohort studies.

Enter the study type in cell L4 & data in 2x2 TABLE cells D12, E12,

D14 & E14. PRESS F9 to calculate rates and chiquare statistic.

------------- ------------- - ------------- ------------- - ------------- ---- ---- ---------- ------------------- ------------- -------------

What is the study type ? ................................... 3

(Enter 1 for cross-sectional, 2 for case-control, 3 for cohort)

======== ======== ========= ======== ========= == == ====== =========== ======== ========

2x2 TABLE DISEASE

F | +ve -ve | Totals Rates p(D+/F)

A ------------- | ------------- ------------- | ------------- ---------

C +ve | 140 100 | 240 0.583

T -ve | 60 100 | 160 0.375

O ------------- | ------------- ------------- | ------------- ---------

R Totals | 200 200 | 400

The corrected chi-square

statistic is : 15.844

Odds Ratio : 2.333

ASSOC - MEASURES OF ASSOCIATION

------------- ------------- ------------- ------------- ------------- --- ------------- -------------

CASE-CONTROL STUDY: Disease |

------------------ +ve -ve | Totals

------------- ------------- |- --------

Factor +ve 44 706 | 750

-ve 28 2382 | 2410

------------- ------------- |- --------

Totals 72 3088 | 3160

Rates p(F+/D) 0.611 0.229 |

[Press F9 to calculate / Press <Alt>A to return to the menu]

MEASURES OF ASSOCIATION CHISQ (X²)

------------- ------------- ------------- ------------- --- ------------- -------------

Odds Ratio 5.302 Uncorrected 56.865

Pop. OR 1.984 Corrected 54.772

Est. AF 0.811

Est. PAF 0.496

[see below for confidence intervals ]

------------- ------------- ------------- ------------- ------------- --- ------------- ------------- -------------

CONFIDENCE INTERVALS

--------------------

a) Precision based | b) Test based

se(Q)or(ln(Q)) lower upper | X²(uncor) lower upper

------------- ------------- ------------- ------------- --- ------------- ------------- -------------

OR 0.245515 3.280 8.570 | 56.865 3.437 8.179

Pop. OR 0.224381 1.279 3.076 | 1.660 2.370

|

Est. AF n/a 0.695 0.883 | 0.600 1.022

Est. PAF 0.074644 ** 0.350 0.642 | 0.367 0.625

** based on Walter, SD., Int J Epi, 1978; 7:175-182.

Note: test based intervals are reasonable if .2<OR<4.

------------- ------------- ------------- ------------- ------------- --- ------------- ------------- -------------

COHORT STUDIES: Disease |

-------------- +ve -ve | Totals Rates p(D+/F)

------------- ------------- |- ------------- -------------

Factor +ve 120 80 | 200 0.6000

-ve 30 270 | 300 0.1000

------------- ------------- |- ------------- -------------

Totals 150 350 | 500

[Press F9 to calculate / Press <Alt>A to return to the menu]


----------------------------------- -------------------

Relative risk = 6.000 Uncorrected 142.857

Odds ratio = 13.500 Corrected 140.486

Attributable rate = 0.500

Attributable fraction = 0.833

[see below for confidence intervals - press <Pg Dn>]

------------- ------------- ------------- ------------- ------------- ----- ------------- ------------- -------------


--------------------

a) Precision based | b) Test based

se(Q)or(ln(Q)) lower upper | X²(uncor) lower upper

------------- ------------- ------------- ------------- ----- ------------- ------------- -------------

RR 0.18 4.20 8.58 | 142.86 4.47 8.05

OR 0.24 8.42 21.63 | 8.81 20.69

|

AR 0.04 0.42 0.58 | 0.42 0.58

AF N/A 0.71 1.18 | 0.70 0.97


------------- ------------- ------------- ------------- ------------- ----- ------------- ------------- -------------

CROSS-SECTIONAL STUDIES: Disease |

----------------------- +ve -ve | Totals Rates p(D+/F)

------------- ------------- |- ------------- -------------

Factor +ve 140 100 | 240 0.5833

-ve 60 100 | 160 0.3750

------------- ------------- |- ------------- -------------

Totals 200 200 | 400 0.5000

Rates p(F+/D) 0.70 0.50


----------------------------------- --------------------------

Relative risk = 1.556 Uncorrected = 16.667

Odds ratio = 2.333 Corrected = 15.844

Pop relative risk = 1.333

Pop odds ratio = 1.667 [Press F9 to calculate]

Attributable rate = 0.208 [Press <Alt>A to

Attributable fraction = 0.357 return to menu]

Pop Att. rate = 0.125 [See below for confidence

Pop Att. fraction = 0.250 intervals - <Pg Dn>]

------------- ------------- ------------- ------------- ------------- ---- ------------- -----------------------------


--------------------

a) Precision based b) Test based

se(Q)or(ln(Q)) lower upper X²(uncor) lower upper

------------- ------------- ------------- ------------- ---- ------------- ------------- -------------

RR 0.12 1.24 1.95 16.67 1.26 1.92

OR 0.21 1.55 3.52 1.55 3.50

Pop RR 0.11 1.07 1.67 1.16 1.53

Pop OR 0.19 1.15 2.43 1.30 2.13

AR 0.05 0.11 0.31 0.11 0.31

AF N/A 0.19 0.49 0.19 0.53

Pop AR 0.05 0.04 0.21 0.06 0.19

Pop AF #N/A #N/A #N/A 0.13 0.37

Confidence intervals for measures of association with explicit SEs are

calculated in the usual manner. Walter's formula (I. J. Epi. 7:175:182)

for SE(PAF) was used. Other CIs were calculated by mapping.

If the upper CL exceeded 100% for "fractions", 100% is used.


------------- ------------- ------------- ------------- ------------- ---- ------------- ------------- -------------

KAPPA - measures the agreement between two tests.

Enter the data in cells C8, D8, C10, D10.


------------- ------------- ------------- ------------- ---- ---------- -- ------------- -------------

TEST 2

T+ T- |

|

TEST 1 T+ 3 2 | 5

T- 0 995 | 995

------------- ------------- | ----------

3 997 | 1000

% Observed agreement ......................................... 99.8 %

% Expected agreement ........................................... 99.2 %

% Actual agreement beyond chance .................................. 0.6 %

% Potential agreement beyond chance ............................ 0.8 %

Kappa .............................................. 0.75

COMBINE - Sensitivity, specificity and positive predictive value of

combined tests with test results interpreted in SERIES and in PARALLEL.

Enter data in cells D8 to D11 and F8 to F11.

Enter True Prevalence, if known (as a proportion) : ............... 0

PRESS F9 TO CALCULATE. PRESS ALT<E> TO ERASE.

------------- ------------- ------------- ------------- ------------- ------------- ------ ------------- --- -------------

Test 1 Test 2 Diseased Not Diseased

+ - 3 15

- + 0 0

+ + 61 1

- - 9 525

------------- ------------- -------------

73 541

------------- ------------- ------------- ------------- ------------- ------------- ------ ------------- --- -------------

Sensitivity Specificity PV+ve

Test 1 (3+61)/73 = 87.7% (0+525)/541= 97.0% n/a

Test 2 (0+61)/73 = 83.6% (15+525)/541= 99.8% n/a

Parallel (3+0+61)/73= 87.7% (525)/541 = 97.0% n/a

Series (61)/73 = 83.6% (15+0+525)/541= 99.8% n/a

------------- ------------- ------------- ------------- ------------- ------------- ------ ------------- --- -------------

SENSITIVITY, Test 1 =

SPECIFICITY, Test 1 =

SENSITIVITY, Test 2 =

SPECIFICITY, Test 2 =

( In Parallel - SENSITIVITY

- SPECIFICITY

- PV +ve

In Series - SENSITIVITY

- SPECIFICITY

- PV +ve

DETECT : Sampling to detect disease

------------- ------------- ------------- ------------- ------------- ------------- ------------- -------------

1 - Determines n of N animals to be examined to be 95/99/99.9% sure

that at least one diseased animal will be detected if disease is

present.

2 - Determines the expected maximum number of cases, with confidence a,

if n of N animals are examined and found to be negative.

DETECT-1

...determining the sample size(n) required to be 95/99/99.9% sure of

detecting disease present in a population(N)...

------------- ------------- ------------- ------------- ------------- ------------- ------------- -------------

Note: enter prevalence and confidence level as proportions.


======== ======== ======== ======== ======== ======== ======== ========

Population size(N): ................................................. 1200

Likely MINIMUM PREVALENCE if disease is present: ........................... 0.002

Likely NUMBER OF DISEASED ANIMALS(D): ................................. 2.4

Required CONFIDENCE LEVEL(a) [ie. 0.95, 0.99, 0.999] : ............... 0.95

The required SAMPLE SIZE(n) is : ..................................... 855

======== ======== ======== ======== ======== ======== ======== ========

A thumb-rule approach (THE RULE OF THREE) is as follows...

Enter 3 for 95%, 4.6 for 99% and 6.9 for 99.9% CONFIDENCE : 3

The required SAMPLE SIZE(n) is : .............................. 855

Adjusting this for SAMPLING FRACTION the SAMPLE SIZE(n) is : 499

======== ======== ======== ======== ======== ======== ======== ========

DETECT-2

...determining the max. no. of diseased animals(D) when a given sample

(n) is examined and found to be disease free...

------------- ------------- ------------- ------------- ------------- ------------- ------------- -------------

Note: enter confidence level as a proportion.


======== ======== ======== ======== ======== ======== ======== ========

Population size(N): .......................................... 0

Required CONFIDENCE LEVEL(a) [ie. 0.95, 0.99, 0.999] : ................... 0

SAMPLE SIZE(n) : .............................................. 0

If n animals test -ve the MAX. NO. of diseased animals(D) is : #DIV/0!

The MAX. PREVALENCE of disease in the pop. : ............................. #DIV/0!

======== ======== ======== ======== ======== ======== ======== ========

A thumb-rule approach (THE RULE OF THREE) is as follows...

Enter 3 for 95%, 4.6 for 99% and 6.9 for 99.9% CONFIDENCE : ....... 0

If n animals test -ve the MAX. PREVALENCE of disease is : ............ #DIV/0!

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praktikum epidemi dasar rev

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