{"id":340,"date":"2009-07-22T21:07:28","date_gmt":"2009-07-22T20:07:28","guid":{"rendered":"http:\/\/moomango.co.uk\/ttfa\/?page_id=340"},"modified":"2009-07-22T21:07:28","modified_gmt":"2009-07-22T20:07:28","slug":"units-of-measurement","status":"publish","type":"page","link":"https:\/\/i-base.info\/ttfa\/learning-resources\/units-of-measurement\/","title":{"rendered":"Units of measurement"},"content":{"rendered":"<p>This page covers two basic units used to count CD4 cells and viral load:<\/p>\n<ul>\n<li>cubic millimetre \u2013 mm<sup>3<\/sup><\/li>\n<li>millilitre \u2013 mL<\/li>\n<\/ul>\n<p>And two advanced units often used in studies:<\/p>\n<ul>\n<li>log value \u2013 log<sub>10<\/sub><\/li>\n<li>percentage \u2013 %<\/li>\n<\/ul>\n<h2 id=\"cubicmm\">Cubic millimetre \u2013 mm<sup>3<\/sup><\/h2>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignright size-full wp-image-341\" src=\"https:\/\/i-base.info\/ttfa\/files\/2009\/07\/dice.jpg\" alt=\"Dice with a side 1mm long has a volume of 1 cubic millimitre\" width=\"128\" height=\"99\" \/><strong>A cubic millimetre measures a very small volume. The length, depth and height of the volume are all 1 millimetre (mm) long.<\/strong><\/p>\n<p>In scientific papers cubic millimetre are sometimes shown as microlitres (\u00b5L) or million parts per litre (10<sup>6<\/sup>\/L).<\/p>\n<p>CD4 count is measured as number of cells in a cubic millimetre (mm<sup>3)<\/sup>. One cubic millimetre is about a drop of blood.<\/p>\n<h2 id=\"millilitre\">Millilitre \u2013 mL<\/h2>\n<p><strong><img loading=\"lazy\" decoding=\"async\" class=\"alignright size-full wp-image-342\" src=\"https:\/\/i-base.info\/ttfa\/files\/2009\/07\/beaker.jpg\" alt=\"Measuring beaker\" width=\"128\" height=\"91\" \/>A millilitre measures a volume of liquid.<\/strong><\/p>\n<p>Viral load is measured as number of copies in a mL.<\/p>\n<p>1,000 mm<sup>3<\/sup> = 1 mL. 1,000 mL = 1 litre.<\/p>\n<h2 id=\"log\">Log value \u2013 log<sub>10<\/sub><\/h2>\n<p><strong>A log value shows a number as a factor of 10.<\/strong><\/p>\n<p>Log values make it easier to deal with big numbers.<\/p>\n<h4 id=\"measure\">Measuring viral load using logs<\/h4>\n<p>Viral load is often measured using a log value.<\/p>\n<ul>\n<li>A 1 log drop in viral load means the amount of HIV has gone down by 90%<\/li>\n<li>A 2 log drop means it has gone down by 99%<\/li>\n<\/ul>\n<p>If your viral load was 20,000 then a 1 log drop equals a 10-fold (10 times) decrease to 2,000. A 2 log drop equals a 100-fold decrease (10 x 10 times) to 200.<\/p>\n<ul>\n<li>A 1 log drop in viral load can mean different things.<\/li>\n<\/ul>\n<p>A drop from 20,000 to 2,000 and from 2,000 to 200 are both drops of 1 log.<\/p>\n<h4 id=\"table\">Table: log = number<\/h4>\n<table border=\"0\">\n<tbody>\n<tr>\n<td>1 log<sub>10<\/sub> = 10<\/td>\n<td>1.5 log = 30<\/td>\n<td>1.7 log = 50<\/td>\n<\/tr>\n<tr>\n<td>2 log<sub>10<\/sub> = 100<\/td>\n<td>2.5 log = 300<\/td>\n<td>2.7 log = 500<\/td>\n<\/tr>\n<tr>\n<td>3 log<sub>10<\/sub> = 1,000<\/td>\n<td>3.5 log = 3,000<\/td>\n<td>3.7 log = 5,000<\/td>\n<\/tr>\n<tr>\n<td>4 log<sub>10<\/sub> = 10,000<\/td>\n<td>4.5 log = 30,000<\/td>\n<td>4.7 log = 50,000<\/td>\n<\/tr>\n<tr>\n<td>5 log<sub>10<\/sub> = 100,000<\/td>\n<td>5.5 log = 300,000<\/td>\n<td>5.7 log = 500,000<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><a href=\".\/log-value-to-number-conversion-table\">Log value conversion table<\/a>.<\/p>\n<h2 id=\"percent\">Percentage \u2013 %<\/h2>\n<p><strong><img loading=\"lazy\" decoding=\"async\" class=\"alignright size-full wp-image-343\" src=\"https:\/\/i-base.info\/ttfa\/files\/2009\/07\/hens.gif\" alt=\"1 in 10 hens = 10% of hens\" width=\"128\" height=\"91\" \/>A percentage shows a number as a proportion of 100 \u2013 the number of parts in 100 parts.<\/strong><\/p>\n<ul>\n<li>1% = 1 in 100<\/li>\n<\/ul>\n<p>Percentages are often used to compare proportions from different samples.<\/p>\n<p>CD4 cells are sometimes counted as a percentage \u2013 the proportion of lymphocytes (white blood cells) that are CD4 cells. A CD4% of 12.5 usually equals a CD4 count of 200 in adults.<\/p>\n<p>Percentages can be made easier to understand by turning them into fractions:<\/p>\n<ul>\n<li>20% = 20 in 100 = <sup>20<\/sup>\/<sub>100<\/sub><\/li>\n<\/ul>\n<p>Sometimes percentages are shown as a decimal fraction of 1 (100% = everything you count = 1). To make a percentage into a decimal fraction, divide it by 100.<\/p>\n<ul>\n<li>20% = <sup>20<\/sup>\/<sub>100<\/sub> = 0.20<\/li>\n<\/ul>\n<h4 id=\"table2\">Table: common percentages and what they mean<\/h4>\n<ul>\n<li><strong>5%<\/strong> = 0.05 = <strong>1 in 20<\/strong><\/li>\n<li><strong>10%<\/strong> = 0.10 = <strong>1 in 10<\/strong><\/li>\n<li><strong>12.5%<\/strong> = 0.125 = <strong>1 in 8<\/strong><\/li>\n<li><strong>16.5%<\/strong> = 0.165 = <strong>1 in 6<\/strong><\/li>\n<li><strong>20%<\/strong> = 0.20 = <strong>1 in 5<\/strong><\/li>\n<li><strong>25%<\/strong> = 0.25 = <strong>1 in 4<\/strong> = a quarter<\/li>\n<li><strong>33%<\/strong> = 0.33  = <strong>1 in 3<\/strong> = a third<\/li>\n<li><strong>50%<\/strong> = 0.50 = <strong>1 in 2<\/strong> = half<\/li>\n<li><strong>66%<\/strong> = 0.66 = <strong>2 in 3<\/strong> = two thirds<\/li>\n<li><strong>75%<\/strong> = 0.75 = <strong>3 in 4<\/strong> = three quarters<\/li>\n<li><strong>80%<\/strong> = 0.80 = <strong>4 in 5<\/strong><\/li>\n<li><strong>90%<\/strong> = 0.90 = <strong>9 in 10<\/strong><\/li>\n<li><strong>95%<\/strong> = 0.95 = <strong>19 in 20<\/strong><\/li>\n<\/ul>\n<h4 id=\"deceive\">Percentages can deceive!<\/h4>\n<p>Percentages show proportions, not actual numbers. It is sometimes difficult to see the whole picture:<\/p>\n<ul>\n<li><strong>A study reports:<\/strong> 80% of people using our new drug had an undetectable viral load at the end of the study.<\/li>\n<li><strong>Questions:<\/strong> how many people completed the study? Was it many people, or only a few? Maybe lots of people dropped out because of side effects!?<\/li>\n<\/ul>\n<p>The report suggests the new medicine worked for 8 in 10 people who took the drug \u2013 when it really worked for 8 in 10 people who completed the study.<\/p>\n<p><strong>When looking at percentages, remember to ask &#8216;percentage of what?&#8217;<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"<p>This page covers two basic units used to count CD4 cells and viral load: cubic millimetre \u2013 mm3 millilitre \u2013 mL And two advanced units often used in studies: log value \u2013 log10 percentage \u2013 % Cubic millimetre \u2013 mm3 &hellip;<\/p>\n","protected":false},"author":2,"featured_media":0,"parent":315,"menu_order":9,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-340","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/pages\/340","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/comments?post=340"}],"version-history":[{"count":0,"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/pages\/340\/revisions"}],"up":[{"embeddable":true,"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/pages\/315"}],"wp:attachment":[{"href":"https:\/\/i-base.info\/ttfa\/wp-json\/wp\/v2\/media?parent=340"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}