Chad

The terms "standard error" and "standard deviation" are often confused.1 The contrast between these two terms reflects the important distinction between data description and inference, one that all researchers should appreciate.

The standard deviation (often SD) is a measure of variability. When we calculate the standard deviation of a sample, we are using it as an estimate of the variability of the population from which the sample was drawn. For data with a normal distribution,2 about 95% of individuals will have values within 2 standard deviations of the mean, the other 5% being equally scattered above and below these limits. Contrary to popular misconception, the standard deviation is a valid measure of variability regardless of the distribution. About 95% of observations of any distribution usually fall within the 2 standard deviation limits, though those outside may all be at one end. We may choose a different summary statistic, however, when data have a skewed distribution.3

When we calculate the sample mean we are usually interested not in the mean of this particular sample, but in the mean for individuals of this type—in statistical terms, of the population from which the sample comes. We usually collect data in order to generalise from them and so use the sample mean as an estimate of the mean for the whole population. Now the sample mean will vary from sample to sample; the way this variation occurs is described by the "sampling distribution" of the mean. We can estimate how much sample means will vary from the standard deviation of this sampling distribution, which we call the standard error (SE) of the estimate of the mean. As the standard error is a type of standard deviation, confusion is understandable. Another way of considering the standard error is as a measure of the precision of the sample mean.

The standard error of the sample mean depends on both the standard deviation and the sample size, by the simple relation SE = SD/. The standard error falls as the sample size increases, as the extent of chance variation is reduced—this idea underlies the sample size calculation for a controlled trial, for example. By contrast the standard deviation will not tend to change as we increase the size of our sample.

So, if we want to say how widely scattered some measurements are, we use the standard deviation. If we want to indicate the uncertainty around the estimate of the mean measurement, we quote the standard error of the mean. The standard error is most useful as a means of calculating a confidence interval. For a large sample, a 95% confidence interval is obtained as the values 1.96xSE either side of the mean. We will discuss confidence intervals in more detail in a subsequent Statistics Note. The standard error is also used to calculate P values in many circumstances.

The principle of a sampling distribution applies to other quantities that we may estimate from a sample, such as a proportion or regression coefficient, and to contrasts between two samples, such as a risk ratio or the difference between two means or proportions. All such quantities have uncertainty due to sampling variation, and for all such estimates a standard error can be calculated to indicate the degree of uncertainty.

In many publications a ± sign is used to join the standard deviation (SD) or standard error (SE) to an observed mean—for example, 69.4±9.3 kg. That notation gives no indication whether the second figure is the standard deviation or the standard error (or indeed something else). A review of 88 articles published in 2002 found that 12 (14%) failed to identify which measure of dispersion was reported (and three failed to report any measure of variability).4 The policy of the BMJ and many other journals is to remove ± signs and request authors to indicate clearly whether the standard deviation or standard error is being quoted. All journals should follow this practice

A lot of times, it's a matter of personal preference. I prefer standard error because it takes into account sample size, and the larger the sample, the lower your calculated error becomes. Also, standard deviation seems messy to me, because you can have error bars that overlap by quite a bit and still have a significant difference. With standard error (unless you have a large enough sample size), typically if the error bars overlap or are close to each other, the differences are insignificant. Not always, but many times. To me, the data usually looks "cleaner" with standard error.

And really, SE is not that hard to calculate anyway. Once you have the SD, you divide the SD by the square root of the sample size, and that's your SE.

Source: http://www.protocol-online.org/biology-forums-2/posts/11239.html

Error bars in experimental biology.pdf

protocol.docx

Hot-plate test in rats

This method, devised by N.B. Eddy and D. Leimbach, is a well-known pain test for assessing the acute heat pain sensitivity in normal rats and has been designed to perform rapid precise screening of narcotic type analgesic drugs (morphine, codeine, …). The latency of licking one of the hindpaws is measured on a hot plate (52 oC, cut-off: 60 s). The increase in the latency is the measure of the antinociceptive effect. The advantage of the test is that there isnt any restrain for the animals during the procedure. When a central analgesic is administered to the animals, this reaction time is markedly increased. Hot-plate is usually used for exploring supraspinal analgesic effects. The organisation of the test is mainly supraspinal.
Yaksh, T.L. and T.A. Rudy, 1977, Studies on the direct spinal action of narcotics in the production of analgesia in the rat, J.Pharmacol.Exp.Ther. 202, 411.

Apparatus : Thermostatically controlled metal plate

see : Analgesic meter - hot plate

Carrageenan-induced inflammatory pain test in rats

This is a well-known pain test for assessing the thermal hyperalgesia after carrageenan-induced inflammation in rats. The advantage of the test is that there isn’t any restrain for the animals during the procedure. The test is sensitive to opioids. The organisation of the test is mainly spinal, although the response is influenced by supraspinal centers too.
Hargreaves, K., R. Dubner, F. Brown, C. Flores and J. Joris, 1988, A new and sensitive method for measuring thermal nociception in cutaneous hyperalgesia, Pain 32, 77.

Apparatus : plexiglass testing chamber with a glass floor

see : Analgesic meter - Plantar(Hargreaves'),

Paw-withdrawal test in rats

This is a well-known pain test for assessing the acute heat pain sensitivity in normal rats. The advantage of the test is that there isn’t any restrain for the animals during the procedure. The test is sensitive to opioids. The organisation of the test is mainly spinal, although the response is influenced by supraspinal centers, too.
Yaksh, T.L. and T.A. Rudy, 1976, Chronic catheterization of the spinal subarachnoidspace, Physiol.Behav. 17, 1031.

Apparatus :

see : Analgesic meter -

Randall-Selitto Test

This is a well-known pain test for assessing the acute physical pain sensitivity in normal rats.
Randall, L.O & Selitto, T.J.(1965)Arch. J. Pharmacodyn. 111. 409-419.

Apparatus :

see : Analgesic meter - Randall-Selitto.

Hot water tail-immersion test in rats

This is a well-known pain test for assessing the acute heat pain sensitivity in normal awake rats. It measures the latency when the rat removes its tail from the hot water bath (51.5 oC, cut off time: 20 s). The background of the test is a short-lasting restrain for the animals during the procedure. This test is very sensitive to opioids. The organisation of the test is mainly spinal although the response is influenced by supraspinal centers, too.
Janssen, P.A.J., C.J.E. Niemegeers and J.C.G. Dony, 1963, The inhibitory effect of fentanyl and other morphine-like analgesics on the warm water induced tail withdrawal reflex in rats, Arzneim Forsch./Drug Res. 13, 502.

Apparatus : Hot water bath with electronically controlled temperature.

see : Water-bath

Hot-water tail immersion in mice

Test for analgesic effects, where the latency for a rat to remove its tail from a hot water bath is measured. Morphine and other analgesic compounds are active in this test.
Wong et al., (1996). Effects of NMDA receptor antagonists on inhibition of morphine tolerance in rats: binding at mu-opioid receptors. European Journal of Pharmacology 297: 27-33.

Apparatus : Hot water bath with electronically controlled temperature.

see : Water-bath

Tail-pinch test

The “tail-pinch test” is preferentially performed on mice. A paper clip is applied to the tail root of the mouse and the latency of the biting response to the clip is measured. The pressure of the paper clip is adjusted so that the biting response of the naive mice is normally about one second. To prevent tissue damage, a cut off time of 6 sec is recommended. (Huong, N. T. T. et al, 1997)
Apparatus : Clamp.

see :

Tail-flick test in rats( D'Amour & Smith's method )

Test for analgesic action, where a heat stimulus produced by a light beam is applied to the tail of a rat. The tail-flick latency is recorded as the time onset of stimulation to the withdrawal of the tail from a light beam. Analgetics generally prolongate of tail-flick latency, and this can be used as a simple screening assay for this type of compounds. Heat and cold tail flick times are useful for testing spinal analgesia. Spinal analgesia was tested by the response times to heat or cold tail flick times in a water bath at 50 or -5 °C (Hendry, J. A. et al 2000). An infrared source can also be used focused by a parabolic mirror on the rat tail.
The classical tail flick test has been designed to perform rapid precise screening of analgesic drugs on the rat tail, according to D'Amour & Smith.
D'Amour F E. and Smith D. L. (1941): A method for determining loss of pain sensation. Journal of Pharmacology and Experimental Therapeutics 72: 74-79.

Apparatus : Analgesia Meter,

see : Analgesic meter - Tail-flick(D'Amour & Smith)

Writhing syndrome in mice

Test for analgesic action of a compound. A mouse is injected with a local irritant ( 0.6% acetic acid i.p after administration of the drug ). The first reading (0 min) was taken and the experimenter counts the number of writhing episodes. Analgetics generally decrease the number of episodes, and this test is used as a simple screening assay for this type of compounds.
Turner RA. In screening methods in pharmacology. New York: Academic Press, 1965;1:27-30.

Hendershot L C, and Forsaith J, (1959): Antagonism of the frequency of phenylquinone-induced writing in the mouse a by weak analgesic and non-analgesic. Journal of Pharmacology and Experimental Therapeutics 125: 237-240.

Apparatus :none

Plantar Test ( Hargreaves' Method )

It basically consists of a movable infrared generator which the operator glides below a glass pane upon which the rats are deposited in a 3-compartment Perspex enclosure.

Apparatus : chamber for planter

see : Analgesic - Plantar(Hargreaves')

Plantar Von Frey

By using a peripheral neuropathy model (chronic pain) in rats, the mechanical allodynia (von Frey test) and thermal hyperalgesia is performed to evaluate compounds with potential analgesic activity. The analgesic effect of drugs and other types of compounds can be measured with the system.

Apparatus :

see : Von-Frey or Dynamic Plantar Aesthesiometer

Electrical : Pododolorimeter method

Pododolorimeter method of Charlier et a1. Techno aggressometer with partition removed was used to administer the shock ( 1 Hz, 25V, 25msec.).

Charlier R, Prost M, Binon F, Deltour G. Etude pharmacologique d’un antitouesif: le fumarate de phenethyl (propyne-2yc)-4 propionoxy- 4-piperindene. Arch Int Pharmacodyn Therap 1961:134:326-32.

Apparatus : eletric stimulator

출처 : http://www.servlab.co.kr/servlab/analg.php