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Errors in the Kaplan MCAT Comprehensive Review/My $0.02 worth on MCAT Prep Books

Discussion in 'Pre-Medical - MD' started by panacea, Nov 30, 2001.

  1. panacea

    panacea Junior Member
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    Hi Everyone:

    I found some errors in Kaplan's MCAT review book (ISBN 0-7432-0186-8) <a href="http://www.kaptest.com/catalog/Product.jhtml;$sessionid$GUHPCGIDXPBW3LAQTEFXBNNMCCMQM2HB?PRODID=123228&CATID=8" target="_blank">]http://www.kaptest.com/catalog/Product.jhtml;$sessionid$GUHPCGI DXPBW3LAQTEFXBNNMCCMQM2HB?PRODID=123228&CATID=8</a> . I've been in contact with Kaplan and the person responsible (Scott - ask me and I can put you in touch with him) for errata got in touch with me, acknowledged there were some problems, was grateful for the input and said he did some work to ensure it gets fixed.

    I would put a link to an errata --&gt;here&lt;-- but Kaplan unfortunately hasn't created an on-line one (I recently searched 'errata' on Kaplan's web page). I suggested they make an errata and gave them a fair deal of time to do so (the letter I wrote them was dated September 6th 2001). If an errata is posted in the next little while I'll post a link.

    In the mean time, I have for the benefit of others, attached the gist of my letter. It is complete with references, if you don't want to trust me that I've got it right.

    Generally, I have a favorable opinion of the Kaplan Review book, despite of the errors in the one section. It is well organized and explains everything in a simple language. I found it especially useful for the writing section which, owing to my background in the physical sciences, wasn't a section I was confident I could do well in.

    Personally, I would recommend getting a couple of review books. One of my favorites is Baron's MCAT (ISBN 0-8120-9730-0). It, my opinion, is especially good for the physical sciences section and takes a somewhat more sophisticated approach than other books. It is also compact, concise and for those of you a bit weary about math -- it has a good math review section. In addition, it has four complete and tough practice tests.

    The Gold Standard prep book is also quite good. I'm not quite as familiar with it as the other two discussed above. In terms of the language and sophistication I'd say it lies somewhere between Baron's and Kaplan and is also well organized.

    Apologies that the post got a bit long. Nevertheless, I hope my explanations/corrections are informative, comprehensible and don't go totally overboard.

    Cheers! :)


    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Bits of My Letter to Kaplan
    (with a few little edits)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Dear Dr. Rochelle Rothstein:

    I have found a number of serious errors in the Solids and Fluids section of the Kaplan MCAT Comprehensive Review. They are described below along with corrections and suggestions. The presentation of the material in that section in my opinion only furthers misunderstanding. I hope my comments can help address this issue in a positive way. The cover of the book says good until 2003. Perhaps you can post an errata on <a href="http://www.kaplan.com." target="_blank">www.kaplan.com.</a>

    ...


    ERRORS
    1. Streamlines
    "Streamlines are the paths followed by tiny fluid elements (sometimes called fluid particles) as they move." This statement (given on page 671) is simply not true.

    An excellent description of streamlines is given by Anderson (Anderson, JD Jr, Fundamentals of Aerodynamics, 2nd Edition, McGraw-Hill Inc., New York, 1991.).

    Paraphrasing Anderson (p. 123):
    A streamline is a curve whose tangent at any point is in the direction of the velocity vector at that point.

    In unsteady flow the streamline pattern is different at different times because the velocity vectors fluctuate with time in both magnitude and direction. Generally, streamlines are different from pathlines. A pathline can be visualized as a time-exposure photograph of a given fluid element, whereas a streamline pattern is like a single frame of a movie. When a flow is unsteady, the streamline pattern changes and each frame of the movie is different.

    SUGGESTION:
    Restrict the discussion to steady flow. Pathlines and streamlines are the same thing in steady flow.

    2. Shear Stress
    The note on page 674 about shear stress is wrong.
    "Only solids can experience shear stresses, liquids and gases can't."

    Shear stresses exist in fluids and gases. In fluids they are of biological and pathological significance. The statement would be correct, in most cases, if it was specified that the fluid and gas are at rest.

    ------------------------------------
    ASIDE
    ------------------------------------

    GOING OVERBOARD
    ************************************
    Technically speaking blood is thixotropic and can support a shear stress at rest. This is little known because it is not important under normal physiological conditions (at least for large vessels), as shown by Dutta and Tarbell and Gijsen et al. (Dutta A, Tarbell JM. Influence of non-Newtonian behavior of blood on flow in an elastic artery model. J Biomech Eng. 1996 Feb;118(1):111-9. Gijsen FJ, Allanic E, van de Vosse FN, Janssen JD. The influence of the non-Newtonian properties of blood on the flow in large arteries: unsteady flow in a 90 degrees curved tube. J Biomech. 1999 Jul;32(7):705-13.).
    ************************************

    High shearing stress in the blood can lead to red blood cell break down. This is why high speed pumps (which impose high velocity gradients on the flow and thus high shearing stresses) can not be used to move blood. This is one of the many difficulties associated with the design of mechanical hearts, lung-heart machines and ventricular assist devices. Shear (among other things) keeps blood from clotting. The knowledge that shear prevents clotting and very low shear or stasis promotes clotting has been used in the treatment of aneurysms. (Mericle RA, Lanzino G, Wakhloo AK, Guterman LR, Hopkins LN. Stenting and secondary coiling of intracranial internal carotid artery aneurysm: technical case report. Neurosurgery. 1998 Nov;43(5):1229-34.).

    Most important biologically are the shear stresses the blood imposes on the artery wall. Atherosclerotic lesions are much more likely to form in regions of disturbed wall shear stress (e.g. carotid sinus). This has been known for some time. The landmark paper in this area was published in 1969 (Caro CG, Fitz-Gerald JM, Schroter RC. Arterial wall shear and distribution of early atheroma in man. Nature. 1969 Sep 13;223(211):1159-60.).
    ------------------------------------
    ------------------------------------
    SUGGESTION:
    Solids can support shearing stresses, fluids and gases when at rest can't.

    -- The above manages to keep it relatively simple and lies only a tiny bit.


    3. Bernoulli's Equation.
    From the description of the Bernoulli's equation it is apparent the author of this section does NOT understand it properly. This becomes clear when one reads the "Real World Analogy" on page 672. The first part about how velocity varies with proximity to the wall is correct for a long straight tube and steady flow (which incidentally is not related to Bernoulli's equation). The second part (which claims Bernoulli's equation is valid between a point on the wall and a point in the center of the artery) is wrong. In reality (for a straight section of a blood vessel) there is a negligible pressure difference between the fluid at the wall of the blood vessel and the center of the blood vessel. This incidentally is an assumption in the famous Hagen-Poiseuille equation that relates pressure gradient, flow and vessel diameter.

    Bernoulli's equation, generally speaking, is not valid when applied across streamlines. This is the reason why the "Real World Analogy" is wrong. Bernoulli's equation can only be applied throughout the flow field if the flow is steady, incompressible and irrotational. A description of this exception, along with a derivation based on the irrotationality condition, is given by Roberson and Crowe (Roberson, JA, Crowe TC, Engineering Fluid Mechanics, 6th Edition, John Wiley & Sons Inc., New York, 1997. -- pp. 143-145). An excellent description of Bernoulli's equation complete with a list of six limitations is given by White (White, FM, Fluid Mechanics, 3rd Edition, McGraw-Hill Inc., New York, 1994. -- pp. 158-159).

    ------------------------------------
    ASIDE
    ------------------------------------
    Examples of how Bernoulli's equation can be applied are in the Pitot tube (used to measure wind speed) and Venturi meter (used to measure volumetric flow). It is my opinion that while Bernoulli's is useful in many cases it does not help one very much in describing blood flow.

    A good deal of the confusion about Bernoulli's equation rises when it is compared to the equation P=Q*R (P=pressure, Q=flow, R=resistance). This equation, it seems, is often taught to students in physiology courses. It is used because it is analogous to the familiar equation V=I*R (Ohm's law), and is useful for explaining the general concept of 'pressure drives flow'. This consideration aside it is often quite misleading. P=Q*R implicitly assumes a constant cross-sectional flow area and incorrectly suggests flows against an adverse pressure gradient (where the up-stream pressure is lower than the downstream pressure) are impossible. The equation also obscures the fact that gravity can drive the flow (P=Q*R ignores gravity). Rivers and waterfalls are not driven by a pressure gradient (they are driven by gravity). Furthermore, it should be noted that P=Q*R (where R is a constant) is only true for laminar flow in a long horizontal straight pipe (known as Hagen-Poiseuille flow). R is, generally speaking, a non-linear function of Q. In fully turbulent flow P is approximately proportional to Q^2 (i.e. R is approximately proportional to Q).
    ------------------------------------
    ------------------------------------

    SUGGESTION
    ----------
    What I think a premed should understand about Bernoulli's equation:
    1. The proper definition of a streamline (for steady flow).
    2. Bernoulli's equation applies along a streamline.
    3. Pressure, 'rho V squared divided by two' (rho*V^2/2) and 'rho g h' (rho*g*h) represent energies and their sum is constant (axially) along a pipe/or vessel of variable diameter if no energy losses (e.g. friction) or sources (e.g. pumps) are present ---(this is Bernoulli's equation in words).
    The energy explanation of Bernoulli's equation can be demonstrated by rewriting the dimensions of the individual terms. One can, for example, show that pressure is really work per volume (1 Pa = 1 N/m^2, 1 N/m^2=N*m/m^3, 1 N*m/m^3 = 1 J/m^3 - J (joule) is the unit for work and energy, m^3 is a volume).**
    4. In a real system frictional losses are present. The sum P+rho*V^2/2+rho*g*h when traveling along a streamline is NOT a constant (it usually decreases due to friction). In most cases the frictional loss is apparent as a pressure loss (i.e. P downstream &lt; P upstream --- in medical language: P distal &lt; P proximal).
    5. One does not always detect a pressure loss in a frictional flow. If the cross sectional area is increasing in the flow direction, it is possible that the pressure may be increasing in the flow direction (P distal &gt; P proximal!).***

    ** I think this is the easiest way of understanding Bernoulli's. There are a number of ways Bernoulli's equation can be understood. Anderson (Anderson, JD Jr, Fundamentals of Aerodynamics, 2nd Edition, McGraw-Hill Inc., New York, 1991.) discusses them shortly on page 159.

    *** P=Q*R (incorrectly) suggests this type of flow is impossible.


    Things I think a premed does NOT need to know:
    1. Irrotational flow and when Bernoulli applies to the whole flow field (this requires a knowledge of calculus).
    2. The magnitude of pressure loss due to friction and under exactly what conditions flow can proceed against an adverse (negative) pressure gradient (this requires an understanding of non-dimensional groups -- Reynolds number, roughness to diameter ratio and geometry associated loss coefficients).
     
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  3. Yogi Bear

    Yogi Bear 2K Member
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    Wow...so have you taken the mcats yet? did they end up giving you anything free? I heard you're supposed to get like $50 and a free t-shirt or somethign if u find a mistake.
     
  4. 8675309

    8675309 Member
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    Maybe Im the only one thinking this, but why have you gone to all this trouble. Quoting research material in an open letter to Kaplan, do you really think they care? No. I realize that you do research in coronary anastomoses or something along those lines but why do you feel the need to show off that ability. I got a 37-39 on the MCAT and all that stuff you worried/complaining about would be in retrospect totally worthless for studying for the MCAT. Why make people more anxious than they already are about the MCAT, do they really need to know that blood can experience sheer forces, probably not. You on the other hand got a 10 in the physical sciences so despite all you research to the contrary you still have figured out what is needed to score high on the MCAT. 1) be a good test taker 2) take so many practice tests under test conditions that it becomes second nature, That's it, the great secret to the MCAT

    Do you really have so much free time that you can waste, yes it is a waste, it posting and sending letters about this?
     
  5. nezlab99

    nezlab99 Senior Member
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    8675309-
    Hittin below the belt and bragging about your score are wastes of time.
     
  6. brandonite

    Moderator Emeritus 7+ Year Member

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    I couldn't agree more, nezlab99... I don't think anything is really achieved by going after another member here.

    Anyway, I do think that it is a serious problem if there are mistakes in the Kaplan materials. I've heard about other errors before. While these aren't the kind that would be a problem to your average premed student, that is not to say that they should just be ignored...
     
  7. 8675309

    8675309 Member
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  8. Yogi Bear

    Yogi Bear 2K Member
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  9. panacea

    panacea Junior Member
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    meddude03 - I have taken the MCAT - twice.
    I didn't get anything for my effort, with the exception of the feeling that I helped fix something that might not have been fixed otherwise.


    8675309 - Why have I gone to the trouble?
    I've read some journal papers on blood flow from physicians that just aren't right. This in a small way might effect some positive change.

    Also, I got some nice feedback when I posted a while back. I probably can't help the ones that helped me, but I figure I can perhaps help some others. I imagine a few people here might have a genuine interest in understanding the material. I didn't write the bit to intimidate.
     
  10. Resident Alien

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    8675309


    not him again. :rolleyes: :eek: :mad:
     
  11. ken

    ken Member
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    I have to agree with 8675309. I mean, come on, you didn't think the OP was showing off? That was the most ridiculous post I have ever seen. Trying to help people, my a$$.

     
  12. panacea

    panacea Junior Member
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    I'm a bit disappointed in how negative some of the responses have been. I'll admit to over doing it, but I honestly didn't mean to intimidate anyone or spew just for the sake of it.

    My study strategy has been, skim a source that has more than you need, construct a big picture and then learn the material you've been asked to cover.

    Also, I didn't pretend the errors I found are going to be the difference between a good result and a bad one. I agree that the stuff would only help with a few questions, if any.

    This has brought back in focus the fact that I've lived a rather sheltered undergraduate life. The usual premed experience seems to be little more than one mean-spirited competition, where if you understand something you keep it a secret in the hope that the others will lose marks there. A resident once told me things change in med school. Truly sad is that the usual premed experience is the closest the majority of the applicants come to getting there.
     
  13. Yogi Bear

    Yogi Bear 2K Member
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    panacea...so how'd u do the 2nd time on mcats?
     
  14. nezlab99

    nezlab99 Senior Member
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    8675309
    I can't believe that you are making this much of an ass of yourself and assuming that I am the isecure one. Why are you making a big deal out of all of this? Why do you let it bother you that much? Why are you trying to be so offensive? Quit assuming that there is something wrong with everyone but yourself.
     
  15. panacea

    panacea Junior Member
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    meddude03

    The second time around I got VR 9, PS 10, WS O, and BS 13. I can't help but think it is ironic that I did better in the BS than the PS!
     
  16. The Fly

    The Fly Senior Member
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