EPP 2007 EPP 2007 Assessing uncertainty and other changes - PowerPoint PPT Presentation

EPP 2007 EPP 2007 Assessing uncertainty and other changes UNAIDS/WHO Working Group on Global HIV/AIDS & STI Surveillance

UNAIDS Estimation & Projection Package 2007 UNAIDS Estimation & Projection Package 2007 • Objectives – Allow national counterparts to build models of their epidemics � Geographically appropriate � Containing the key sub-populations – Provide short-term projections of HIV prevalence (<5 years) – Serve as input to Spectrum for assessing incidence, impacts, ART, etc. 2007 en 2

EPP interface takes you through the steps EPP interface takes you through the steps 2007 en 3

What basically does EPP do? What basically does EPP do? • Fits plausible epidemiological model to existing data • Modified Reference Group model – 4 fitting parameters r – controlling the rate of growth f 0 – he proportion of new risk pop entrants t 0 – the start year of the epidemic φ – behavior change parameter • …for concentrated epidemics d – average time in group (duration) 2007 en 4

UNAIDS Reference Group model UNAIDS Reference Group model 50 40 φ % HIV+ 30 f 0 20 t 0 r 10 0 2007 en 5

EPP’ ’s s job: fit the model to the data job: fit the model to the data EPP 70 60 50 % HIV+ 40 30 20 10 0 0 5 0 5 0 5 0 5 0 8 8 9 9 0 0 1 1 2 9 9 9 9 0 0 0 0 0 1 1 1 1 2 2 2 2 2 2007 en 6

New features in EPP 2007 New features in EPP 2007 • Uncertainty for generalized epidemics – Bayesian melding • Review mode • Changes to the fitting and calculations (under the hood) – Full exploration of possible solutions for r, f 0 , phi and t 0 – Speed improvements • Improved calibration – Including adjustments for multiple national surveys • A larger interface 2007 en 7

New features in the interface EPP 2007 EPP 2007

EPP 2007 – – review mode review mode EPP 2007 • Can open a projection w/o changing it • Disables saves • Indicated two ways: – Title bar says “Review mode” – “Save & continue” becomes “Continue” • Two ways to exit – On Workset Page, click “Edit” mode – On any page, hit “Save a copy” 2007 en 9

Review mode – – the interface the interface Review mode 2007 en 10

Changes to “ “Save a Copy Save a Copy” ” Changes to • When you “Save a copy” – Makes a copy of the current workset with the name you specify – Loads that copy – Restores the page you were on 2007 en 11

Slider sensitivity adjustments Slider sensitivity adjustments New button Adjust sliders 2007 en 12

Slider sensitivity panel Slider sensitivity panel 2007 en 13

Major changes - Uncertainty EPP 2007 EPP 2007

Uncertainty in the global AIDS epidemic, Uncertainty in the global AIDS epidemic, 1990 − − 2005 2005 1990 Number of people (0–49) 50 5.0 living with HIV Millions % Adult (15–49) 40 4.0 prevalence Number 30 3.0 % Adult of people (15–49) (0–49) prevalence living 20 2.0 with HIV 10 1.0 0 0.0 1990 ‘91 ‘92 ‘93 ‘94 ‘95 ‘96 ‘97 ‘98 ‘99 ‘00 ‘01 ‘02 ‘03 ‘04 2005 Year Source: UNAIDS/WHO, 2006 2007 en 15

What have we learned about What have we learned about the Reference Group model? the Reference Group model? • Sometimes the EPP fitter selects strange curves • This is a “feature” of the Reference Group model • Some data sets are not constraining 2007 en 16

Many curves can fit the same data – – Many curves can fit the same data some we know are not realistic some we know are not realistic Source: Adrian Raftery 2007 en 17

EPP 2007 EPP 2007 So we’re going to do the process we mentioned before…. Try many different combinations of r, f 0 , phi and t 0 ….

Some countries with a lot of data have only Some countries with a lot of data have only a few curves that fit – – data constrains it data constrains it a few curves that fit 8 curves Botswana through 2003 – 50,000 curves tried 2007 en 19

Other countries with more limited data have a Other countries with more limited data have a lot of curves that fit – – data does not constrain data does not constrain lot of curves that fit 240 curves Senegal urban through 2003 – 50,000 curves tried 2007 en 20

EPP 2007 EPP 2007 In this variation, lies a way of assessing uncertainty Countries where the data limits us to only a few curves have less uncertainty about the epidemic

Assessing uncertainty – – Bayesian melding Bayesian melding Assessing uncertainty Developed by Adrian Raftery Raftery & Leontine Alkema for EPP & Leontine Alkema for EPP Developed by Adrian • Randomly generate lots of curves – Select a lot of (r, f0, phi and t0) values • Compare the curves with the data – Calculate “goodness” of fit and assign a weight – Likelihood function is used as a weight on the curve – High likelihood means a curve is a good fit and gets a high weight • Resample a smaller number of curves from the curves originally calculated – But, resample according to the weight assigned – The curves that fit better get picked more often • Keep the resampled curves, throw away the others • These curves provide an estimate of the uncertainty 2007 en 22

Bayesian melding first generates many curves Bayesian melding first generates many curves 70 High weight – fits the data 60 closely 50 % HIV+ 40 30 20 10 0 0 5 0 5 0 5 0 5 0 8 8 9 9 0 0 1 1 2 9 9 9 9 0 0 0 0 0 1 1 1 1 2 2 2 2 2 2007 en 23

We then resample the curves according to the We then resample the curves according to the weights – – selecting ones that best fit the data selecting ones that best fit the data weights Zimbabwe urban data With 3000 resamples, only 6 high likelihood curves get selected 2007 en 24

If we do enough curves, If we do enough curves, we can estimate the uncertainty we can estimate the uncertainty 95% of resampled curves fall between two dashed lines Botswana with 200,000 curves, resampling gives 46 unique ones 2007 en 25

And countries where data trends are less clear And countries where data trends are less clear will show more variation in curves will show more variation in curves That is, they show more uncertainty Zimbabwe urban 200,000 curves, gives 55 unique ones 2007 en 26

And countries with very limited data And countries with very limited data will not constrain the possible curves much at all will not constrain the possible curves much at all Uncertainty about the future is huge Senegal urban 50 curves, gives 240 unique ones 2007 en 27

Uncertainty decreases Uncertainty decreases as more data becomes available as more data becomes available Very uncertain Botswana urban using only data through 1995 – data still rising 2007 en 28

Uncertainty decreases Uncertainty decreases as more data becomes available as more data becomes available Uncertainty is getting smaller Botswana urban using only data through 2000 – points starting to level off 2007 en 29

Uncertainty decreases Uncertainty decreases as more data becomes available as more data becomes available Uncertainty is narrowing as epidemic levels off Botswana urban using all data through 2002 – data has leveled off 2007 en 30

EPP 2007 EPP 2007 This has now been built into EPP for generalized epidemics

Wow!!! So how do I do that? Wow!!! So how do I do that? • You use EPP as you normally would – Open a new generalized workset • Workset page – Define the sub-populations in your epidemic • Define Epidemic page – Enter the demographics • Define Pops page – Enter the HIV data for each • Enter Data page – Enter your calibrations (Calibrate page) • …And then 2007 en 32

The EPP 2007 Calibration page The EPP 2007 Calibration page • Four calibration options – Adjust to level measured in general pop survey (recommended) – Adjust by average amount based on survey to ANC prevalence ratio in generalized epidemics (recommended) – Scale a sub-population’s HIV by a given factor – Don’t do calibration (the default) 2007 en 33

The EPP 2007 Calibration page The EPP 2007 Calibration page 2007 en 34

The EPP 2007 Calibration page The EPP 2007 Calibration page • If you choose to adjust to a general population survey, for each sub-population enter: – Survey prevalence – Year survey was done – Standard error on survey (need to locate this) – Sample size • Up to 3 survey results in different years 2007 en 35

Then you come to the Projection page Then you come to the Projection page New button “Assess uncertainty” 2007 en 36

EPP 2007 EPP 2007 Before you do anything else, press the assess uncertainty button This will bring up the EPP 2007 uncertainty interface

The EPP 2007 uncertainty interface The EPP 2007 uncertainty interface Curve generation Results display Start, Stop, and Status What to do with results Advanced options Display controls 2007 en 38