# Presentation: 071699

## Models to Inform Recommendations About Preventive Services

- Perspective of the United States Preventive Services Task Force

## Behavioral interventions
inability to maintain fidelity with treatment
inability to control provider effects

Quality improvement interventions
inconsistency of implementation
difficulty in withholding interventions with what is viewed as high face validity
contamination

- inability to maintain fidelity with treatment
- inability to control provider effects
- Quality improvement interventions
- inconsistency of implementation
- difficulty in withholding interventions with what is viewed as high face validity
- contamination
**	**

**An RCT for Every Topic is an Unattainable Goal: Technical**

## Community programs 
Insufficient number of communities willing to be randomized
Inability to maintain fidelity with program parameters
Need for adaptability to gain cooperation
Need for adaptability to achieve effectiveness
Contamination

- Insufficient number of communities willing to be randomized
- Inability to maintain fidelity with program parameters
- Need for adaptability to gain cooperation
- Need for adaptability to achieve effectiveness
- Contamination
**	**

**An RCT for Every Topic is an Unattainable Goal: Technical**

## The Parachute Problem

- Do we really NEED an RCT?
**	**“....the effectiveness of parachutes has not been subjected to rigorous evaluation by using randomised controlled trials....we think that everyone might benefit if the most radical protagonists of evidence-based medicine organized and participated in a double-blind, randomized, placebo-controlled crossover trial of the parachute....”
**	**
**	*****Sackett. Parachute use to prevent death and major trauma related to gravitational challenge: systematic review of randomised controlled trials.  BMJ 2003;327:1459-61.***

## It is not feasible to conduct an RCT for every topic for which clinical decisions must be made

**	**

**But Even More Importantly**

## CRC: Options in 2008

- Something found in stool
- Occult blood using guaiac (gFOBT)
- Un-rehydrated
- Rehydrated
- Occult blood using test that is more sensitive than guaiac
- Fecal DNA
- Something “seen” in the colon
- Visual
- Flexible sigmoidoscopy
- Alone
- With FOBT (several options)
- Colonoscopy
- Radiographic
- Dual contrast barium enema (DCBE)
- CT colonography (CTC)

## Number of RCTs: CRC Screening Type of Test

- 9 strategies against no screening
-    **Would require 8 two-arm trials or a very large 8-arm trial (unrehydrated gFOBT already done)**
- 9 strategies against all other possible strategies alone
- E.g. more sensitive FOBT versus unrehydrated FOBT
-        FOBT versus optical colonoscopy
-        optical colonoscopy versus CT colonography
-        flexible sigmoidoscopy versus fecal DNA etc. etc. etc.
**Would require 35 two-arm trials or a very large 8-arm trial**

## Starting age
Age 40 or 50 or something else for CRC
Age 16 or 21 or something else for cervical cancer
Stopping age
Stop age 75 versus 85 for CRC
Stop age 65 versus 75 for cervical cancer
Screening interval
Every 5 years versus every 10 years versus once in a lifetime for CRC
Every year versus every 3 years versus every 5  years for cervical cancer

- Age 40 or 50 or something else for CRC
- Age 16 or 21 or something else for cervical cancer
- Stopping age
- Stop age 75 versus 85 for CRC
- Stop age 65 versus 75 for cervical cancer
- Screening interval
- Every 5 years versus every 10 years versus once in a lifetime for CRC
- Every year versus every 3 years versus every 5  years for cervical cancer

**It May be Impossible or Nearly Impossible To Conduct a Valid RCT**

## Long-Term Financial Planning 
What if I live to age 95, how much money will I need to live comfortably considering inflation and the rate of return on my investments? (MAKE A MODEL) 
What do you recommend to assure that I don’t run out of money? (USE THE MODEL TO INFORM THE RECOMMENDATION)

- What if I live to age 95, how much money will I need to live comfortably considering inflation and the rate of return on my investments? (MAKE A MODEL)
- What do you recommend to assure that I don’t run out of money? (USE THE MODEL TO INFORM THE RECOMMENDATION)

**Models: What If.....**

## Short-Term Financial Decisions 
What if I buy a car that gets 65 miles per gallon, how much money will I save over five years considering the number of miles I drive? (MAKE A MODEL). 
Should I buy a car that costs $34,000?  (USE THE MODEL TO INFORM THE DECISION)

- What if I buy a car that gets 65 miles per gallon, how much money will I save over five years considering the number of miles I drive? (MAKE A MODEL).
- Should I buy a car that costs $34,000?  (USE THE MODEL TO INFORM THE DECISION)

**Models: What If.....**

## Policies  
What if people in developing economies use the same number of barrels of crude oil per capita as people in the United States, in what year will the world supply of crude oil be exhausted?  (MAKE A MODEL) 
What does the committee recommend to assure that there is sufficient availability of energy for future generations?  (USE THE MODEL TO INFORM THE RECOMMENDATION)

- What if people in developing economies use the same number of barrels of crude oil per capita as people in the United States, in what year will the world supply of crude oil be exhausted?  (MAKE A MODEL)
- What does the committee recommend to assure that there is sufficient availability of energy for future generations?  (USE THE MODEL TO INFORM THE RECOMMENDATION)

**Models: What If.....**

## Daily Decisions 
What if I leave the office at 3 o’clock instead of 5 o’clock, how long will it take to get back home over the Bay Bridge considering the month, the day of the week and the weather? (MAKE A MODEL). 
Should I leave early today to be sure that I am not late to dinner at the Smiths?  (USE THE MODEL TO INFORM THE DECISION)

- What if I leave the office at 3 o’clock instead of 5 o’clock, how long will it take to get back home over the Bay Bridge considering the month, the day of the week and the weather? (MAKE A MODEL).
- Should I leave early today to be sure that I am not late to dinner at the Smiths?  (USE THE MODEL TO INFORM THE DECISION)

**Models: What If.....**

## Conscientious: careful, thorough, meticulous

Explicit:  open, clear, plain

Judicious: sensible, well thought out

- Explicit:  open, clear, plain
- Judicious: sensible, well thought out

**Models in the Context of Evidence-Based Medicine**

- Modelers need to do this better

- Good models meet this criterion

- Good models meet this criterion

## Results From Good Models: Does This Information Help Make a Recommendation? The USPSTF Thinks the Answer is Yes.

|  | Start Age | Stop Age | 

Interval | 

Estimated Number of Life-years Gained per 1,000 Screened |
| --- | --- | --- | --- | --- |
| Test for cancer A | 20 | 65 | 5 yrs | 265 |
| Test for cancer A | 25 | 65 | 5 yrs | 263 |
| Test for cancer A | 30 | 65 | 5 yrs | 243 |

**Results From Good Models: Does This Information Help Make a Recommendation? ****The USPSTF Thinks the Answer is Yes.**

## Results From Good Models: Does This Information Help Make a Recommendation? The USPSTF Thinks the Answer is Yes.

|  | Start Age | Stop Age | 

Interval | 

Estimated Number of Life-years Gained per 1,000 Screened |
| --- | --- | --- | --- | --- |
| Test for cancer B | 40 | 85 | 8 yrs | 301 |
| Test for cancer B | 40 | 85 | 15 yrs | 267 |
| Test for cancer B | 40 | 85 | once | 244 |

**Results From Good Models: Does This Information Help Make a Recommendation? ****The USPSTF Thinks the Answer is Yes.**

## Not taught in most medical schools 
Generalized antipathy; many people hate anything called a model
Assumptions are made; these often look like guesses 
The model assumptions are often opaque

- Generalized antipathy; many people hate anything called a model
- Assumptions are made; these often look like guesses
- The model assumptions are often opaque

**Models: the Pushback **

## MODELS

- Information from models reduces bounds estimates
- Information from models is better than information obtained by guessing, even informed guessing
- A recommendation based on a good model is better than silence and is often the best we will ever do

## All models are wrong, some are useful.

                                      George Box 1979

-                                       ***George Box 1979***

## 
DISCUSSION

- DISCUSSION