Model inputs

A user in New York asked for clarification of some of the inputs to the Clinic Planning Model Generator. Here is my response for everyone’s use.

Patient arrival batch size: Do the patients arrive in batches (because of transportation like buses)? If not, then just enter 1.

Batch size variance:What is the variance of these arrival batches? If they are always the same size, then enter 0.

Interarrival time variance: What is the variance of the interarrival times? If you do not have any data, you can enter 0 as an assumption.

Estimating cycle time

A Clinic Planning Model can estimate the cycle time of a POD (clinic) – the average time that patients spend in the POD (from the time they arrive until the time they leave). This estimate is based on a steady-state approximation of the POD; that is, it assumes that the arrival rate (in patients/hour) remains constant. The arrival rate is determined by the number of people, the number of days and hours, and the number of PODs.

What about when the arrival rate is not constant? Some periods may have large arrival rates, others smaller. The cycle time will be larger when the arrival rate is larger. One approach to handle this is to change the model inputs to model each period and determine the cycle time for each period.

For example, suppose that one expects one period of time when patients will arrive to a POD at a rate of 100 per hour and another period of time when the arrival rate will be 500 per hour. For the first period, let the “Size of the population to be treated” equal 100, with 1 day for treatment, 1 hour of operation, and 1 clinic site. The outputs will provide the cycle time for this period. For the second period, change the “Size of the population to be treated” to be 500. The outputs will provide the cycle time for this period. If you plan to change the staffing for different periods, then change these as well.

Preparedness for Kids

This is not about modeling, but it’s certainly relevant to preparedness planning: The Washington Post had an article by Mary Beth Sheridan on Wednesday, November 14, 2007, about government agencies teaching kids about emergency preparedness. The front-page article headline is “Boys and Girls, Can You Say Anthrax?”

The article states that preparedness experts hope that kids will encourage their families to get ready. They are using in-class lessons, coloring books, cartoon characters (with names like “Ready Eddie,” a character created by Howard County, Maryland), and web sites (like the DHS Ready Kids site). The program in Washington, D.C., is a six-week series of lessons at eight schools, and it focuses on a wide range of emergencies, according to the article, which also mentions that the American Red Cross Masters of Disasters program is used at some other schools in the Washington area.

I found on the Ready Kids site some basic information for making an emergency plan as well as a quiz, downloadable comic strips about planning, and some online games (including one that resembles the classic card game Concentration). The content is similar to that of other programs aimed at adults, such as the PLAN TO BE SAFE campaign that Montgomery County, Maryland, APC developed. My employer was recently reminding all of its faculty and staff to have emergency plans, so I can sympathize with the need to have something that will get a family’s attention. And the kids’ programs discussed in the article are not that different from the firefighters telling us to have a fire escape plan when they visited my elementary school years ago.

As always, feel free to post a comment or send a note to

Specialized Flu Clinics

The drive-through flu clinic by Howard County, Maryland, was one of nine flu clinics in the county this fall. These demonstrate the idea of having different types of clinics focused on specific populations. An “Adult Clinic” for those over 50 years old was held during the day on a Friday. A Flumist clinic was held on a weeknight evening for people from age 2 to 49 without chronic health problems; this would have been popular with families. Even the drive-through had two areas: one for adults, and the other for families. (Six other clinics are being held in the next month in different locations across the county to catch everyone else.)

Using different clinics to target different populations makes a lot of sense from an operational and logistic point of view. It moves each clinic away from the “job shop” model that tries to serve everyone (with a lot of complexity and waiting) and makes it closer to the “manufacturing cell” (or “focused factory”) model that can be more efficient by serving one type of customer. From a modeling perspective, focusing on one type of customer reduces the variability in the system; and variability is a root cause of congestion and other problems.

Using Excel 97

A planner from California wrote about some problems using the Clinic Planning Model Generator with Excel 97. We investigated and found that the software used a function that was not available in Excel 97. We created a specialized version with a substitute function that performs the same calculation but is compatible with Excel 97. If you need it, please let me know at

Open Source and the Web

After one of my talks in Seattle, a colleague suggested that we should consider open source software instead of relying on Microsoft Excel for the Clinic Planning Model Generator. His comment was motivated by Massachusetts’ intention to use open source software. I have not heard of any other states moving in that direction.

Perhaps the point will become moot, however, for we are currently developing a web-based clinic planning model to avoid problems with Excel, especially different versions and operating systems.

Drive-through flu clinic

Yesterday, for the second year in a row, University of Maryland students conducted a time study of a drive-through flu clinic Howard County, Maryland. Data from this time study will be used by Howard County public health planners for evaluating the performance of their clinic; we will use the data to validate our mass arrivals clinic model. You can read more about the event in this article.

Hello world!

Welcome to the Public Health Preparedness Modeling blog. This blog is here to support public health emergency preparedness planners and the researchers who are developing models for this community. I welcome comments about the subjects covered here and particular models.

I’m Jeffrey W. Herrmann, the blog moderator. My background is in operations research and industrial engineering. Over the last few years I’ve been working in this area, particularly on models of mass dispensing and vaccination clinics (aka PODs). Please visit our project web site for more details about this project.

Please comment on the posts here or send me a note if you’d like to post something. You can reach me at